Basement Insulation
Written by Todd Fratzel. 
Basement Insulation – Walls
I’ve started insulating the basement walls in our new basement storage room. I’m attaching 1-1/2″ extruded polystyrene foam insulation board by DOW. I used a special Styrofoam adhesive to adhere the foam board to the concrete (you can also use “Great Stuff Pro” foam in a can). The foam board I am using comes with a tongue and grove so installation is pretty easy. Just cut the boards to length, apply some adhesive and press it against the wall.
If you’d like to see a video of this type of approach check out our DIY Basement Insulation Video.
You’ll notice that I installed the boards horizontally. Since doing this project we’ve been installing them vertically at work and it’s much easier to do! Placing them vertically makes it much easier to keep them from falling down while the adhesive cures.
Seal Insulation Joints
After I installed all of the polystyrene foam insulation I sealed all of the joints with Tyvek tape. Tyvek tape is a really strong tape that will stay adhered to the foam board and it keeps out moisture. Concrete holds a tremendous amount of moisture so creating a moisture barrier is essential.
Frame Basement Walls
Once all the insulation was in place I started framing up 2×4 walls. I’m going to place the walls directly in front of the foam insulation and then insulate the wall cavities with fiberglass insulation. You’ll need to nail the pressure treated plate of the wall to the concrete with a Trigger Tool Kit, 22 Caliber. By doing the combination of insulation materials I can achieve approximately a R values of 16.
After I finish framing and insulating the walls I will i
nstall luan paneling over the framing. I plan to install 2′ deep shelves all around the room for our storage.
Check out my previous post, Finished Basement Step 1 – Insulation where I explain the methods of insulating in detail. Also check out How To Insulate Basement Walls. There is also some really great information at the Building Science Corporation.
Insulated Concrete Floors
For this project we’re not insulating the concrete floors because we have radiant heated slabs. However, if your home doesn’t have radiant heat and you’re looking for information on that topic then we recommend you read How To Insulate A Concrete Floor.
Related posts:
- Basement Vapor Barrier For Basement Insulation
- DIY Basement Insulation Video
- Basement Insulation Detail
- How To Insulate Basement Walls
- Basement Insulation | Spray Foam Installation Video
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I am thinking about a basement project and need to insulate before any framing.
Why use a combination of foam panels and batts, wouldnt it have been quicker to use 2″ foam board for about an r12? Also how are you insulating the sill plate?
2″ of foam board only gives you about R=8 at most. I used a combination because it’s cheaper and the kraft face gives me a good “breathing” vapor barrier. The sill plate is insulated with R38 fiberglass. I probably should have done that with foam as well.
I thought the whole point of using foam panels was that it replaced fiberglass, which does not handle moisture well.
Please explain…I’m about to start a large basement finishing project…thanks!
There is no single correct answer. First off it depends on the R value you need. Here in NH for my basement and my house the way it was designed I need a minimum of R13 in the basement walls. I also wanted a minimum of 2×4 stud walls to hang drywall and other wall materials from. I also wanted to minimize the amount of floor space I took up with the walls. So…having said all that I chose to use 1″ of blue board, a 2×4 wall insulated with R11 fiberglass. The blue board is an excellent moisture barrier and will prevent the moisture from getting to the insulation. All the joints are taped to prevent any air and moisture.
You could also do the whole job with blue board. Again, depending on the product blue board is about R=3.8 per inch so you’d need to decide how much you need.
I recently finished my basement and followed this approach:
1) Use a closed cell foam board insulation. I used 3″ thick board, glued to the cement wall. This insulates the wall(is not a vapor barrier). Closed cell will not trap moisture but allow it to transfer thru, insulating the wall will help balance the temperature difference between in the conditioned air space and the basement wall. Its this temperature difference that will cause condensation and moisture to form.
2) I built a 2×4 wall, 1 inch away from the foam board. This wall was insulated with non-faced R13 insulation. The 1″ void is important, if moisture does migrate thru the foam board(it will) you want a channel for it to escape and not get trapped in the insulation. Yes this uses more floor space, but I am willing to give up a few inches of floor space to be sure I don’t have a mold/moisture issues down the line.
3) I also used a flooring system call DriCore. I sealed my basement floor with DriLok, then laid the DriCore over it. I made sure the ventilation channel under the floor connected to the void in the wall. I installed floor vents(4″x8″) thru the DriCore in several places in the basement and connected one vent to the cold air return on my HVAC system to draw air thru the system.
I also used pressure treated wood for the sill and galvanized steel studs. I figure the less ‘food; I provide for mold the better. The steel studs were a breeze to work with and the walls came out perfectly straight.
Its been 5 years since this was done and so far the basement is very dry and feels fresh – no humidity feel that many basements can get.
I live in Northern Ohio, so winters are cold and summers are humid. My basement never had a water problem, but before it was finished it had a humidity problem. My dehumidifier ran constantly, filling its 2 gallon tank up every day, now it takes about three/four days for it to fill up the tank.
Hope this helps.
the one thing it looks like you’re lacking is a moisture control system. There’s no vapor barrier or reflective material to bounce the heat back into the space. Currently it looks like you’re installing the insulation right on the wall. you’re going to loose a lot of heat that way.
putting it directly on the foundation wall doesn’t allow anything to breath and can actually build up moisture behind them…
don’t mean to be a downer, but i had to say something.
Actually..the blue board acts as a vapor barrier….if you read the entire post you’ll see that I’ve sealed all the joints with Tyvek tape. I’ve actually taken apart a wall built this way after 5 years and it looked like new.
What adhisive did you use?
We are in the process of putting up foam board (Owens Corning 1 1/2″ and we cant get the Loctite Foam Board Adhisive to work. Should we nail them in? or possibly screw them in using BIG washers?
Our basment walls are cinder block. Any help would be appreciated.
Thanks
I don’t remember the name of the adhesive, however, it didn’t hold the blue board in place right away. I used temporary supports to hold the blue board in place over night until the adhesive cured. Then I framed the wall in front of it so there really wasn’t anyplace for the insulation to go.
Using the blue board as vapor barrier, wouldn’t it trap moisture between your concrete wall and the blue board?
It is certainly likely to trap moisture between the concrete and insulation. However, the vapor barrier is actually helping keep warm moist air (finished side) from contacting the cold concrete surface and condensating.
I just brought a house and the previous owner put in some 2×4 and batt in the basement, and add a plastic film vapor from top to bottom.
We saw some of the bottom 2×4 turned black,
so we remove some of the insulation from the bottom, and found that the most of them are moist.
We are worry that it may lead to mold problem, so we removed the insulation from the lower part of the wall. The basement now is quite a bit colder, and we are not sure what we should do.
The water table is high and the basement has a sump pump. That maybe the source of the moisture that went between the wall and the vapor barrier.
Any suggest on what I should do?
Leave an air gap like the other poster suggest?
Honestly….without seeing photos and understanding the situation it’s hard to say. You definitely need to get this taken care of. If you’re seeing black material on the wood then that is a sure sign of mold! Mold growth MUST be taken care of properly. I would suggest you have several people look at the problem to help you come up with a plan of attack.
I am starting to finish my basement which I gutted two years ago. The first thing I did last year was install fiber Glass Batt insulation between the ceiling joists. I found out later maybe this was a waste of time. Would it be a good idea to simply remove it and use it on the foundation walls. The batts do vae vaor barriers. I don’t mind the work ,but I don’t want to throw money away either.
Appreciate any advice.
Henry Homeowner
Is it necessary to frame in a 2×4 wall, or can the drywall be glued directly to the form board if fiberglass insulation is not needed?
I would frame the wall. You won’t be happy with drywall glued to the blue board as the insulation doesn’t really adhere well to concrete.
I have a 4inch wide sill plate sitting on a 8 inch wide concrete foundation. Ive brought the wall framing right up to the ceiling joist. What type of insulation do I use to fill in the gap between the top of the concrete foundation and floor joist and wall framing
Any advice will be appreciated
Henry Homeowner
@ Henry – The space along the rim joist can be insulated with several things. I personally like to use foam board and foam the gaps with great stuff. You could also use fiberglass.
A landscape designer recommended using Styrofoam to build up the entire back yard by 24″then cover it with white marble rock. Have you heard of anyone doing this. She said there could be areas that are cut through for plants and soil added there.
@ Backyard Foam – I’ve never heard of this type of application. However, in my previous profession I used to design bridges and there’s a new technique for building bridge approach structures that involves burying large foam blocks in the ground to minimize loads (foam is much lighter than soil). However, I’m not sure why your landscaper would even suggest this approach.
My basement walls are made of concrete blocks and their are also concrete block columns that stick out every 12 feet. Would your method for concrete walls apply for concrete block walls and would you frame around the concrete block columns?
Same method applies for concrete block walls. I’d frame around the columns as well and apply the blue board to the columns too.
I’m finishing my basement and I’m thinking about taking this approach for insulating the around the sill area. My house is 3 years old and I live in Michigan. Currently there is unfaced fiberglass insulation (probably R-19)tucked in the area. I’m thinking of leaving the insulation and sealing off the area with foam board R-5. Will the foam board act as a vapor barrier along with the insulation and keep the warm air from contacting the cool wall and creating condensation. Or am I creating more of a problem doing it this way?
In theory what you propose sounds reasonable. However, I think I’d be more inclined to remove the fiberglass and install the foam directly against the sill plate and rim joist.
We are looking to totally refinish our basement. We live in Wisconsin and had flood damage last year. Just had out walls beamed with 4″ iron beams. What would you suggest for framing and insulating the walls? Though maybe we would use treated wood for the framing, but not sure what to use for insulating. The walls are cinder block. Also, what would you suggest for finishing the basement floor, its a poured concrete floor that had self-adhesive tile on the floor. Looking for something that might retain heat. Any help would be appreciated.
@ Joel – Not sure exactly what your situation is. Do you have any photos? You could email them to me, (my email is on the home page). What caused the flood damage? Is the basement typically dry? Send me more info and I’ll try to give you some advice.
Todd, I stumbled across your sight and really need some advise on a new construction basement insulation project. We built our home in 2006, moved in in 2007. Pennsylvania was in between building codes regarding basement insulation. The inspector made the builder insulate the basement walls that are exposed (walkout basement). The builder framed the walls and put up R13 fiberglass with the aluminum looking facing. As soon as we moved in, the temps dropped and we noticed water coming out of the insulation. Long story short, it appears the warm moist air is getting behind the insulation and condensing. We will actually have ice formation on the walls (that will melt as soon as the temps come back up). We have had mold growth start. The builder has washed his hands of the problem. I was initially thinking to clean the area to rid the mold, then have the cavities spray foamed with a closed cell foam. I am not thinking that we should remove the framing, and attach foam board, then replace the framing. Can you give me any input on this?? Thanks.
@ Scott – I’d definitely recommend you remove the fiberglass insulation and get rid of any potential mold problems that you and your family might be exposed to.
I’m not sure it’s really that warm air is hitting the concrete, more that the concrete is still very damp and the water has no place to go.
You can certainly spray foam the cavities for a very good insulation job that will take care of your problem.
I have an old kit house, a 1954 National, kind of like the sears-roebuck houses that were build cheap and quick so the exterior framing is 2×3. I have fiberglass batt R15 and Now I want to envelope the house. My idea is to use both tyvek therowrap and 1in foam board. I don’t want to create problems with moisture. Can I use both? which should go on the sheath first, the foam or wrap?
@ realnick – The housewrap should be the outer most layer. It’s very common today for folks to install a layer of foam board prior to installing new siding on the home. Be sure to seal all the joints in the foam board. I think you’ll realize a huge difference in the energy performance of your home after this project.
[...] Insulating basement walls in cold climates is a great way to keep your home warmer and drier. However, special care should be used when insulating concrete basement walls. Below grade concrete foundation walls are very cool and damp. If you were to insulate the walls with regular fiberglass batt insulation it is very likely that a mold problem would develop. [...]
[...] written several posts about how to insulate basements, How To Insulate Basement Walls and Basement Insulation. One of the best ways I know how to insulate a basement is using a combination of polystyrene foam [...]
I am about to start my basement. I plan on using blue board on the concrete walls, then 2X4 studs with batt between the studs. My question is do I need to install a vapor barrier on the inside before i drywall?
@ Terry – This question has come up quite a bit lately. I’d like to say I have a definite answer about that situation. I myself have used kraft faced insulation in this situation. There is some literature with some of the foam insulation manufacturers that suggests you should not use a vapor barrier. For me the decision comes down to the thickness of the foam board. In my case I was only using 1-1/2″ thick foam which will still be somewhat cool. In that situation it seems prudent to use a vapor barrier to eliminate the possibility of warmer, moist air entering the cavity and condensating on the foam board.
Again, I think you’ll get numerous answers to this question. Best of luck and sorry I can’t be more specific.
I have put the blue foam arround my pony wall then sraping over top. My question is, can I use wood paneling over top. I have heard that if the foam catches fire it will release chemicals. I did not want the expense of drywall. thanks
Most building products today will release some sort of bad chemicals if they catch fire. Not much different than composite wood products, carpet, etc. Paneling can be used over the top. Again, be sure you insulate sufficiently to prevent any condensation from occurring behind the paneling.
I am currently finishing the basement in my 60 year old house and after much research have decided to follow the technique described here – 1″ blue board glued to the concrete block walls, then 2×4 stud walls with kraft-faced R13 insulation between the studs, with a 1″ gap between the stud walls and the blue board. Here are some observations I’d like to share with others that find this site…
1. If your concrete walls are sealed with a product such as drylock, as mine are, then the dow adhesive that’s right next to the blue board at the big box store won’t work. The fine print on the tube says it’s not recommended for use on sealed concrete. So I used Great Stuff expanding foam to adhere the blue board to the concrete. It worked great. For the most part, the boards didn’t need to be held to the wall while the foam cured. I just propped some 2x4s against the foam at at 45 degree angle to hold it there.
2. Before taping all of the joints with tyvek tape, it’s a good idea to fill any wider ones with spray foam first. You’re bound to have some joints that aren’t quite snug if you have to make any cuts to go around any fixtures such as water or gas lines.
3. In addition to taping all of the joints with tyvek tape, you must seal the entire perimeter of the completed blue board wall with spray foam. Taping the joints stops the from getting behind the boards through the inter-seam joints, but you need to stop air from getting behind there from the top, bottom, and side edges of the blue board wall. Before you start building your stud walls, make sure that there is no way for air to get between the blue board and the concrete wall. This will significantly reduce the risk of water condensing between the blue board and the concrete.
I built a new home this past summer on a 5ft crawl. The inspector would not allow blueboard insulation without it being drywalled due to fire code. So I installed 6 mil plastic to the concrete poured foundation allowing a 15 inch overlay to the floor. Then used R21 foil faced insulation tucked into the floor joist down to the floor. In certain areas I’ve just noticed condensation behind the plastic and in some places damp insulation. Anyway to fix this issue?
@ Joe – Unfortunately I’m not sure what you can do. I think your inspector was a bit premature in his ruling. Most blue board has a fairly good flame spread rating and is really only a concern in areas with an ignition source such as a mechanical room. I’m really not sure the code prohibits blue board based on it’s flame spread rating. It’s something I’d want to look into a bit and you may want to call the inspector and make him show you where it’s prohibited in the code.
What’s the best way to solve this problem now? Tear it out and use the blueboard. Someone reccomended cutting the bottom foot of insulation to allow for air flow.
@ Joe – I hate to say it but for a long term solution you really need to get rid of the fiberglass.
I have an energy star home with blanket insulation on the basement walls. There are horizontal nailing strips at top, middle and bottom. I have learned that neighbors have had mold problems with the same method of insulation.
I have thought of taking off the blanket insulation and putting a layer of Owens fanfold 1/4 inch r value 1 as a vapor barrior and taping the seams. Is this thick enough polystyrene for this? I then wanted to put the blanket insulation back over the Owens fanfold. Would this stop mold growth? If this isn’t acceptable I would probably use 1 inch polystyrene build a 2×4 wall and then drywall. The cost is just a lot more. I don’t need the space just want to save on heat.
Thank you
Glen Gribble
Hudsonville MI 49426
@ Glen – You need at least 1″ minimum of foam to stop the moisture. You can certainly re-use the blanket insulation if it’s dry and mold free.
Hi Todd,
I’m about to re-finishing a basement with new internally framed walls in a similar manner and found this whilst trying to answer the following questions: two of my concrete walls have just been poured and all of the walls are partial concrete foundation and framing on top. Which of the following is the best approach:
(i) fasten the foam to the concrete portion of the wall and leave the upper portion untouched. (Concern is the newness of the concrete and inherent moisture content and the lack of a moisture barrier in the upper portion)
(ii) fasten the form to the outside of my new internal walls first whilst horizontal and erect the walls in sections. I feel the benefit would be in the ability to create a full height moisture barrier *and* leave an air gap next to the concrete to let it breath naturally.
Thoughts?
- Paul.
@ Paul – If I understand your question right you have a lower concrete wall with a short pony wall framed above. Typically in this scenario (I have this situation in my basement) I like to install foam board on the face of the concrete and on the top of the concrete (portion that’s exposed). Be sure to seal the foam on top with spray foam (great stuff works well). Then You can frame a wall in front of the concrete; either full height or the height of the wall, thus creating a bit of a shelf. In either scenario you can finish insulating the wood framed walls with fiberglass or whatever material you’d like.
Thanks Todd. How long should I wait before covering the fresh concrete?
@ Paul – Obviously if you wait awhile it’s better. However, we have done it within a couple months on new builds.
After visiting several different websites (I would highly recommend Building Science.com) We have come to the conclusion to have our basement walls spray foamed – I know it’s more expensive but we feel it gives us the best bang for a buck.
My question is the floor – My wife wants to put 1″ XPS foam panels down with 3/4″ OSB over top to insulate the floor. I am wondering if this will really make a difference? I have remodeled a few basements in the past and have only put down a vapor barrier, thick padding and then carpet. Seemed to me to be warm enough.
If anyone has any insight – It would be greatly appreciated
Thanks, Jeff
@ Jeff – I’ve never put the foam board down on the floor but it’s a practice that many people use in Canada.
Do you feel that I would be alright with vapor barrier, padding and then carpet. Thanks for your input.
-Jeff
@ Jeff – When it comes to flooring I’d say rely on a reputable flooring company on that. Not sure on the vapor barrier.
[...] coming along nicely. I recently wrote a couple of posts, Finished Basement – Step 1 Insulation and Basement Framing and Insulation Update, about how to properly insulate a concrete foundation wall in a basement. Now that the walls are [...]
[...] Check out the followup post, Basement Insulation and Framing Update. [...]
Thanks Todd!
It sounds as if we are going to just put the XPS down then OSB then flooring. Wife want to make SURE that the floor isn’t going to be cold. Thanks again
@ Jeff – Good luck! Email me some photos when you do it, I’d love to share with the readers.
Todd,
I live in PA, and am preping to start finishing my basement. It is 1 1/2 yrs old construction, walk out basement on a sloped lot.
I have a 13×17 section that I would like to make into a storage/workshop. I have numbered the walls.
Wall one is 8′ poured concrete. It is exposed to under the garage.
Wall two is also 8′ concrete, it is exposed to the outside, but mostly above grade.
Wall three is all above grade, but has a 1 1/2′ concrete wall then studded out with 2×6′s. with R13 in between the studs.
Wall 4 (will be interior wall) is exposed to the rest of the basement.
Three questions I have,
1. The room will not be heated, unless I am working in it for extended periods. I will have a portable heater. Would the 1″ foam be enough?
2. Should I insulate the ceiling since this room will not be heated?
3. For the short walls, should I use the foam on them and place a 1×3 all the way up the stud then face with drywall?
P.S what are those short walls called?
-Paul
@ Paul – I’ll try my best to understand your situation but a photo might be a huge help (you could email one to me).
1. 1″ foam will certainly be a big help. Here’s a question though, will this space ever be converted to finished space later? If so you might want to do the whole insulation job now.
2. First of all you definitely should insulate the ceiling above (which is the living space floor) if the basement is not insulated and/or heated. This is actually required by most state energy codes. If you’re wondering about the energy code you can find most states have the requirements online or you could check with your local building officials.
3. Short studded walls are typically called pony walls. You could insulate the lower portion with foam and then stud a short wall in front of that or a full wall all the way up. Either way be sure you seal very well around the concrete including the top of concrete wall.
Best of luck.
Todd,
Here are pictures of the basement.
http://s69.photobucket.com/albums/i64/spechty/Basement/
Todd, should r – 13 fiberglass insulation with kraft paper facing the conditioned space/heated space be used or unfaced after placing studs agains the foamboard in a basemnt. I read alot that one should use unfaced so you don’t create a vapor barrier on both sides. Thanks.
Rick
@ Rick – This question has been asked many times with good reason. The research out there is torn between a vapor barrier and not using one. Here’s my take on it:
In my opinion it depends on the thickness of foam board that you’re using. If you use 1″ or less then I believe you should use a vapor barrier to prevent moisture from entering the framing cavity and condensing on the cool foam board (with only 1″ the foam will still be much cooler than the heated moist air). If you use 2″ of foam then I think you can eliminate the need for a vapor barrier on the warm side. There really is no perfect answer to this situation. Best of luck.
Todd,
Thanks for the reply. After doing more research on the internet, there are alot of conflicting reports on using fiberglass insulation in the basements. Alot of sites claim you sould never use fiberglass insulation in the basement because of moisture and posible mold concerns. I plan on attaching 1″ DOW super tuff-R rigid foam board to the existing foundation, then framing the basement out with metal studs as close to the foamboard as posible. I will fill the cavities between the studs with r – 13 kraft faced fiber glass insulation. The unfaced side will most likely be touching the foamboard. Then I will be using 1/2″ gyspum board as my finish wall covering. I will also run a dehumidifier in the summer months. Do you see any concerns with my plan?
Rick
@ Rick – Your plan sounds very good. Best of luck!
Thanks again for the reply. After doing more research on the internet I can understand where the debate comes from. It looks like the vapor barrier/kraft paper will keep moisture out but if moisture builds up in the fiberglass it will hinder it from leaving the insulation. I guess I’m still nervous about those summer months where the humidity will be higher and the moisture might come in from the outside and the kraft paper will hinder the moisture from leaving the insulation. Like you said, there is no perfect answer. But, if posible moisture or mold build up is more of concern than the overall performance, do you still suggest using the kraft paper? Sorry for all the questions.
Rick
@ Rick – No problem on the questions, this is why I write the site!
There are two things going on here.
1. Moisture from the concrete trying to get into the wall space.
2. Moisture from the finished space trying to get into the wall space.
If either case happens then you have the potential for mold and mildew and reduced effectiveness from the fiberglass.
By properly installing the foam and taping / sealing it at EVERY joint then you’ve pretty much completely cut off moisture from the concrete entering into the wall cavity where the fiberglass is. Again this is one huge reason to use the foam board is to create a vapor barrier and some insulating value. As I said if you only use 1″ then you haven’t completely insulated the cold concrete wall yet. That 1″ foam will still be cool.
If you use an un-faced fiberglass in the 1″ foam situation then you have the potential of moisture traveling through the drywall, through the fiberglass and hitting the cool foam and condensing. From there it will soak into the fiberglass and create a potential mold problem. This is why I am inclined to use kraft faced with only 1″ of foam board.
If you use 2″ of foam board (probably don’t really need fiberglass now) then I think it’s a moot point.
Does that help?
Yes it does, but I have more to say/ask. The only problem is that in my township of Hillsborough, NJ you are forced to fill the wall any wall cavity, even in the basement unless, you have a High Efficiency boiler. Even if I install 2″ foamboard on the wall, I must fill the wall cavity. Therefore, I rather spend a little money on 1″ rather then 2″ foamboard, plus the fiberglass insulation I’m going to have to buy anyway. I think a total r -value of 6.5(1″ foamboard) + 13(fiberglass) = 19.5 will be enough.
I sorry but I forgot to mention that I already painted the foundation walls with two coats of Drylock. Do I still need to seal/tape all the seams of the foamboard? I think the Drylock would be enough of a vapor barrier, but your opinion is the one that carries more weight. I read in one of your other posts that I should seal the seams with the tyvek tape, Correct? If I have a little space between some of my boards, is there something I should fill/seal the gap with? After the addition of Drylock to my information, what do you about the kraft paper. Since I’ll be using a dehumidifier, should I use unfaced to allow the dehumidifer to suck out any moisture that might build of in the fiberglass from either side? Or, will the combination of kraft paper and drylock/foamboard do a better job of preventing moisture from getting in but still allow the dehumidifier to remove the moisture at a slower rate. Or will the dehumidifier have no effect on any possible moisture in the fiberglass? Thanks for any input.
Rick
@ Rick – Drylock is certainly going to help with moisture but I’d definitely take the time to use the tape. It will stop drafts and moisture. Again I’m torn on the vapor barrier issue. I believe that the drylock, foam board and tape will stop moisture from entering from the concrete side. If you don’t put a vapor barrier on the warm side moisture is going to get into that wall and possibly condensate. If it were my house I’d use the vapor barrier (I actually did use it in my house).
Thanks for the help and advice. The only question you didn’t answer is what I should use to fill the couple of small gaps between the foam boards? If the tyvek tape covers the space then is that enough or do I need to use some spray expanding foam insulation. If you already explained this in another article/post please let me know. Thanks.
Rick
@ Rick – Sorry I missed that one….the best solution and easiest is to use a can of “Great Stuff” foam fill. Then use the tape over that as well.
Best of luck with the project.
Thanks.
Rick
Todd, Joe,
regarding the inspector requiring 0.5″ drywall over foamboard, the code reference is IBC 2603.4 “thermal barrier” and also IRC R314.4 “thermal barrier”. The IRC chapter appears to have been completely revised from the 2003 to the 2006 edition and in both codes there are more than a page worth of exceptions none of which apply to Joe’s project af an habitable basement. I own a small remodeling company and I am getting ready to use some of this type product on a clien’t home so I was checking out requirements and codes first. I stumbled onto your site during my research.
@ JRW – As I’ve said many times people have to be very careful and check current codes in their location. It’s also worth noting that many inspectors don’t realize that certain materials actually meet IBC requirements for smoke and flame spread. Something like using vinyl bead board on the ceiling of a temporary building might seem like a bad idea when it comes to fire but if you actually check the spec’s on the material in question you may be quite surprised to find they pass code.
Todd,what do you think about useing your technique but go with the 1/2 Dow blue foam board with R-11 or R-13 craft faced fiberglass ins.between 2×4 studs then 1/2 inch drywall, the 1/2 in. Foam board is half the cost, would it make a big difference?
@ cj – 1/2″ foam board won’t really give you the vapor barrier that you’re going to need in my opinion. 1″ is the minimum I recommend.
Hi Todd, I was hoping you wouldn’t say that about the 1/2inch foam, as I already bought half of what I need and cut the sheets in half to be able to bring them down my basement, what about painting the wall first with some type of waterproof paint and then using the 1/2 inch foam board? would this give me the vapor barrier that I would need, I will buy the 1 inch foam for the rest of the way. or should I double up the 1/2 inch sheets that I have, would the waterproof paint be just the same?
Hi Todd,
I’m remodeling my basement and stumbled upon your website and it has a lot of great info. My home was built in the early 60′s and the basement has minimal moisture. The basement has a cinderblock wall. Does the same principles apply to a cinderblock wall as to cement? I’m planning on using 2 coats of drylok, 1″ Dow foam that you suggested, building the traditional frame wall 1/2 inch space from the foam board, using R13 Kraft fiberglass insulation and a 6mil plastic vapor barrier on the warm side with paperless 1/2″ sheetrock. does this sound like a good plan??? Will the glue you suggested still work on cinderblocks? should I fasten the foam down with furring strips?? Any help would be greatly appreciated.
thanks,
John
@ John – The same principles definitely apply to cinderblock walls. I see one issue with your proposal. DO NOT install kraft faced fiberglass and plastic. Choose one or the other.
Todd, I’m installing 3/4″ extruded polystyrene foam boards from owens corning on my basement walls and will be framing with 2×4′s and insulating with unfaced fiberglass bats and running a dehumidifier in summer. My question is what to do with the 2 or 3 inch section of exposed concrete on the top of the foundation wall that the sill plate does not cover. I sprayed great stuff under the sill plate and filled the rim joist area above with unfaced fiberglass. I thought about using the foam remnants but this would be rather tedious for such a small area. What about simply spraying great stuff in this area? Any thoughts would be appreciated. Thanks for providing such a useful site for us “do it yourself types” John
@ John – First let me say thanks for the compliment about the site!
Secondly, I’d like to point out that 3/4″ foam really isn’t thick enough to stop moisture and water vapor from entering the house via the damp foundation walls. You really need 1-1/2″ to 2″ of foam. Regardless, the top of concrete wall should also be covered in foam board. Don’t sweat it though, take scraps and cut them down on your table saw to the width you need. Then seal them in place with Great Stuff foam. The Foam will seal the joints and hold the foam in place.
Best of luck.
The basement wall adjacent to the stairs is my problem area… the above grade portion is a traditional framed wall which already has the drywall installed. The back of this drywall sits about 1/2″ out from the face of the poured basement wall. So the only way I see to align the drywall is to only use 1/2″ foamboard on this section and attach the drywall… it is only about an 8ft. section… ideas?
@ Jeff – Sometimes there’s not much you can do. I’d recommend at least using paperless drywall or another material at this one location.
I’m looking at finishing my basement. I have block walls just over 8 feet. My question is if I use super tuff r 1 3/8′s with an r value of 8.3 will that be enough or do I need to fill the frames I will build in front with fiberglass batts too? Also, how do I glue to super tuff r with the foil facing the block or the blue side facing the back. It says you get a higher r value with the foil facing the warm side but then if I used batts would that be bad? Or would using 1 inch super tuff r with a 6.5 and filling the frames with batts be better. I plan on putting paperless drywall on the frame.
@ Tom – The minimum R value really depends on the local building code and energy code. I would start by asking your local building code official. The best solution is using as much foam as you can afford and eliminating the fiberglass if you get sufficient R value. The foil should always face the warm “Interior” side.
Hi Todd,
The information on your site is very valuable. I have a home that is approximately 2 years old in the Chicago area. I have 9 ft poured concrete basement walls. I am about to start finishing my basement. A few cracks were forming so I just had the cracks filled by professionals prior to me starting. My main question is regarding the foam board and insulation. I planned on using 1/2″ foam board followed by the frame and then fiberglass insulation between the studs. I was told that the only vapor barrier I would need was on the warm side of the construcion which would mean towards the inside. You have several comments stating that 1/2″ is not enough. I am trying to save a bit of money as well as space – is there any recommendation you would have to still use 1/2″ foam board with an additional plastic vapor barrier followed by the framing, etc. Or is your recommendation that the 1/2″ will pretty much be a waste of money? Thanks for your help.
@ Arpeet – Thanks for the compliment!
1/2″ really isn’t sufficient to stop water vapor from leaving the concrete and entering the framing cavity. You MUST prevent that moisture from getting into your framing and causing a mold problem. I’d rather see you buy 1-1/2″ foam and then do nothing between the studs. In fact, you could frame the walls with 2×3 in that situation to make up for the thicker foam. In the long run, losing another inch will make little difference compared to a bad mold problem. Good luck!
I live in northern Maine where temps get below zero many days of the year and we get at least two to three feet of show each winter. I own a home that was constructed in the early 60′s with a full basement with 8 ft cement walls. I have a partially finished 12 X 22 ft room in my basement that has two exposed cement walls. I have baseboard heating installed on the two cement walls that is never used but is available with a separate zone. There is also a pellet stove in this room that is run during the winter months. Normally my basement is dry but last spring I installed a new hot water furnace that is well insulated and the heat that used to escape from my old furnace is no longer present in my basement. Last summer I discovered a lot of moisture building up in my basement and the only thing I could attribute it too was the lack of heat coming from my furnace during the summer months as it was heating my domestic hot water – something I didn’t think about.
I give you these details just so you’ll have the full facts for this question. I want to insulate the two cement walls that have the baseboard heating by fastening pressure treated 2 x 4′s to the cement wall with the 4″ side fastened to the cement 24″ on center with 1″ blue insulation board glued to the cement wall in between the studs with 1/2 inch moisture resistent gypsum wall board covering it. I plan to start the studding on top of my baseboard heating so I do not have to have a plumber to remove it and reattach it. My finished wall will be the same thickness as the top of my baseboard heating. Should I do this and if so will I run into some moisture problems with only a 1/2 inch air gap between my insulation board and my gypsum wall board? Thanks for any advice.
@ Rob – I personally wouldn’t advocate your plan. If you’re going to take the time and money to build what you propose then I suggest you spend a little more money and move the baseboard. In fact, you might want to consider installing 1-1/2″ to 2″ of blue board on the entire wall. Then you can install 1×3 strapping, nailed through the blue board and into the concrete. Then install your drywall followed by your sheet rock. If you do as you propose it’s EXTREMELY likely that a moisture problem will occur at the base of the base board and propagate into the new wall framing.
Thanks for your thoughts. I would tend to agree with your recommendations.
One question, to nail thru 3 inch strapping & thru 1 1/2 inch blueboard, what length cement nail or screw should I use. How much penetration into the cement should I plan on. Would you use a gun designed to shoot nails into the cement or would you use a hammer drill and attach with screws and how much penetration – would you use anchors driven into the cement then attach the strapping using screws into the anchors? Looking for recommendations. My concern with using a gun that shoots the nails is that it’s easier to split the strapping if the nail hits a rock in the cement & goes off center (based upon my reading). I am concerned that the red plastic piece around the nail appears to keep the nail from penetrating flush with the strapping. What size shell should I use – my cement is 30+ years old. I would be using a Remington single shell pistol gun to shoot the nails. As you can probably tell I’ve never attempted a project like this and any help is greatly appreciated. Thanks
@ Rob – I think you’ll need to experiment a bit with the nails. I think a 3-1/2″ nail will most likely work but you need to buy the ones with the big washers on them. Most likely you’ll need to use a red shell if your gun is rated for them. If that doesn’t work you’ll need to switch over to Tapcon screws. Best of luck!
Thanks for all the info. Really appreciate it.
Hi Todd,
I am about to start my project and I had one a couple of questions.
1. The composite board under the base plate – is this the first item I should start with? Specifically, should I place the composite board, which I believe is 6″, on the floor and butt it up against where the floor meets the wall?
2. Based on the answer to #1, will the foam board start on top of the composite board or will it go all the way to the floor and the composite board is placed on the floor and butt up against the foam board?
3. The composite board/decking material I am planning to use is about 6″ wide. I’m assuming that the 2×4 treated base plate will just sit on the middle of the board?
4. And finally, I will be able to place full sheets of 4×8 foam board on the walls for the most part, but there are going to be some tricky places where I will have to cut around pipes, etc. Is there anything specific I need to do in these cases where the foam board may not necessarily go all the way up to the top of the concrete wall? Specifically do I need to use some caulk to seam up all open areas (I guess this would also apply to when a finished area meets an unfinished area along a single wall – where the foam board ends, should I caulk the end?)
Sorry for so many questions, just want to make sure I get it right.
Thanks
@ Arpeet – Sorry for the delay:
1. Typically composite decking comes in a 1×6 size that’s why we use it. It would be best if it were 3-1/2″ wide. Install the foam board first, tight to the floor. Then install the composite board (you can actually rip it to width with a table saw if you have one).
2. See #1
3. Either rip it down or set the wall flush to the front of the composite board.
4. I like to use “great stuff” foam in a can to seal around everything when you’re finished.
Best of luck.
Basement project,
I will be installing 2″ polystyrene taped & foamed to poured concrete wall. 2″x4″ stud wall on composite board. I was not be putting insulation in wall. Would you install a plastic vapor barrier on the drywall side still? One of the rooms will be a bathroom with the greenboard if it matters. Exhaust fan in bathroom of course.
Thanks
@ Mark – Skip the plastic vapor barrier. The foam board will create a very good vapor barrier. Best of luck.
Todd,
Great posting for us basement DIY. My basement insulation plan is the following and I would like to know your opinion.
I live in Kentucky which is Climate Zone 4. According to the 2007 Kentucky Residential Code, basement wall R value is described as 4/13 with a note stating: “The first R-value applies to continous insulation, the second to framing cavity insulation; either insulation meets the requirement.” My plan is as follows:
1. I have painted the concrete walls with 2 coats of Drylok paint (Latex base).
2. I plan to use “Loctite Power Grab” foamboard adhesive to glue 3/4″ (R-4) Owens Corning Foamular to the bare concrete walls.
4. Stud the walls with 2″x4″, (treated wood on the concrete floor) and install unfaced insulation.
5. The basement is a walk-out basement and the 2″x6″ wood-framed area is insulated with R-19 insulation with kraft paper (paper facing the conditioned side).
6. 1/2 inch drywall will be installed.
Does this sound acceptable to you? I am trying to decide about using kraft-faced R-13 or unfaced R-13 for the cavities based on your earlier advise.
Also, you have recommended using 1″ foam to the walls at minimum but considering my climate zone would 3/4″ not be correct?
Thanks in advance for your advice.
Mike
@ Mike – Thanks for the compliment. I think your plan is pretty good. First off I’d check the specs on the foam board you’ll buy and make sure it provides the R value of 4. Secondly, I’d skip the vapor barrier. The more research I do on the subject tends to lean that way. The fact that you’re in Kentucky certainly helps because your home won’t see the extreme cold temps that we see around here.
Good luck!
Todd,
Thanks for your quick response. Owens Corning 150 “Foamular” board
states on each sheet 1/2″ R=3, 3/4″ R=4 and 1″ R=5 and I purchased the 3/4″ (tongue and groove construction). I will glue the Foamular to the wall, use tyvek tape to tape all seams and fill the studded cavities with unfaced R-13 then drywall over that.
Thanks again for the great posting article – it seems hardly anyone understands how to insulate concrete basement walls, even people that insulate for a living.
Todd,
Sorry to bother you again with another question.
Do you think 3/4″ (R=4) is adequate enough thickness to perform correctly as insuluation/vapor barrier where I live in Kentucky? I am also going to install R13 unfaced in the studded cavities next to the wall as you recommended. If you recommend thicker, can I glue another layer of 3/4″ to the existing 3/4″ I have already glued to the wall? Owens Corning says it has to be 1 1/2″ for a vapor barrior and they also recommend using kraft-faced for the conditioned side but I lean towards your comment that it is not needed because that is why I glued Foamular to the wall was for a vapor barrier.
Thanks again for a great posting and clearing up confusion. Obviously, there are a lot of us that are confused about this.
@ Mike – No bother at all….this is why I run this site!
You really do need at least 1-1/2″ of foam to create that vapor barrier regardless of where you live. I don’t see any reason why you can’t install another layer over the first layer. You can even use “Great Stuff” foam in a can as a great adhesive for it.
Todd, what type of “Great Stuff” are you using? There are many varities. Thx
Also, my there will be an unfinished part of my basement for laundry room, furnace, tools, etc. Do I need to do anything to these walls? I will use FG batts on that end of basement.
Also, I have wires running along top of concrete wall next to mud sill. Any suggestion on insulating that area?
I meant FG batt on that end of basement inside the 2×4 wall that divides finished from unfin1shed space.
@ Jee
1. I like to use low expansion Great Stuff
2. Insulating the walls really depends on your goals and the codes. Unfinished mechanical space is often not insulated. However, some folks do insulate it to improve the overall insulating value of the entire home.
3. You can cut foam to fit between the joists and seal it with Great Stuff.
Todd,
How about using XPS foam w/ plywood on the floor?
Todd, What XPS on wall where no visible water but a breakdown in blockwall has caused very little sand in a couple of spots to come through, which cause Drylock to peel off over time. House built in 1955.
Thanks…
Hello,
I have a question about internal basement waterproofing and this method. My basement was internally waterproofed with a gap between the wall and the floor, and 3 drain tube holes (about 2.5″ tube) flush with the floor (like an access or something.) How do I frame over the holes, will the holes cause moisture between the framing and the insulation? Your website and information is wonderful! keep up the great work!
Be blessed and thank you for your time
@ Jason – Not exactly sure how your basement was waterproofed. Do you have more information or photos? That might help me get a better understanding and therefore allow me to give you some advice.
We are just starting to do some work in the basement of our new home. The builder framed and insulated (batt insulation) the exterior walls. I would like to install foam insulation behind the batt insulation. I just noticed while removing the batt insulation that the builder nailed tar paper behind the insulation. Should I keep it or remove it ?
@ Marc – I would remove it so that you don’t have paper back there that could feed mold one day.
Hey Todd, Mike again to ask another question.
Last year, on one part of the basement I painted the wall with Drylok and framed an 8′ wood stud wall right up next to the concrete wall and installed unfaced fiberglass in the cavities and covered it all with a platic moisture barrier towards the conditioned side. I have not drywalled yet and it is still exposed. Here is my question.
Can/should I remove the fiberglass and install extruded polystyrene foam between the studs? The studs are too close to the concrete to put the foamboard between the stud and wall. If so, please explain how I should do it and if I need to seal where the studs are and how to do it and the thickness (I now have 1 1/2″ thick foamboard on the rest of the walls – 2 layers of 3/4″). If not, should I just live with it?
Thanks again for the help. Great site for us DIY’s.
Mike
@ Mike – First off if it were my house I’d remove the fiberglass, then cut free the wall and move it out away from the wall far enough to get the foam in. I’m not saying to destroy the wall, just cut it free at the base and the top so you can move it. If that’s not an option then I would at least install foam between the studs. Before you do that I’d try to seal the wood with a good sealer. Best of luck!
what about termites? I’m pretty sure that they can chew through foam and or build a “run” up the wall behind the foam. which would make a future termite inspection rather difficult and expensive? Is this an issue?
thanks!
stan
@ stan – Not sure about termites…we don’t have them here in New England.
[...] written several posts about how to insulation basement walls in which I promote the use of foam board insulation as the first line of defense against moisture [...]
hi,
I am re-doing my basement walls that are totaly uneven because they were poured. MY QUESTION IS: I have 1 1/2 xps rigid foam board (pink Stuff) but the boards wont lay flat against the wall due to it being uneven.(1/4 – 1/2 gap) Would that cause problems??? Also, I was told the foam board will not aloud the walls to Breath (Air out). I was advised that to do the basement properly I should place my stud wall an 1″ from the wall (Air gap), fill it with batts and use 6 mil Vapour barreir sheet on top of this. He was totaly against the foam board. Any help would be appreciated..
By the way, my basement walls are 1/2 above grade and 1/2 below grade.
@ Vernon – There are many theories about insulating basements. I can tell you that my experience with the suggested detail that someone else gave you. When fiberglass is installed in that fashion with a vapor barrier over it, it because SOAKED in a very short period of time and moldy. Water that’s trapped behind the foam next to the wall poses no issues in my opinion. The uneven wall isn’t a problem either so long as you seal the joints well.
Good luck.
thanks todd,
so air pockets behind the foamboard from the uneven wall would not cause a problem as long as i seal all the joints (outside)??
could i cut the rigid foam in sections that matches my wall sections. What i mean is my wall has a lot of in’s-and-out’s on the width of the walls but, the length looks to be fairly flat and level. I would spray foam between each of the panels.(at the seam of each poured wall section) the foam board wont be striaght and none of the boards would be touching. Would this method work???
so air pockets behind the foamboard from the uneven wall would not cause a problem as long as i seal all the joints (outside)??
thanks again todd
@ Vernon – Without seeing a photo I’m having a hard time picturing what your basement situation is. However, air spaces pose no problems.
These posts have been great – I am finishing the basement now with poured concrete foundation (house is about 25 years old) – wanted to ask a couple of questions (I am in NY):
1. Dry-Lok’ed the walls in the area I am finishing (25×40) then plan on adding insulation board followed by steel studs and with unfaced fiberglass insulation – do I need to add vapor barrier (I assume not given dry-lok and foam board, just asking)? Also what R-vals should I be looking for in the insulation (I assume R-11 to R-13, but checking)? Don’t want to assume, know what happens there so advice is appreciated….
2. Already a finished room (14×14) in the area with wood studs and faced fiberglass insulation (facing toward inside of room, not exterior walls) with a 2″ air gap between studs/fiberglass and concrete foundation. Do I need to demo this and re-do in same manner as I plan to do in #1, or can I leave it for some time and eventually finish it off or just leave it alone.
Note that I don’t have mold / water issues (knock on wood) – pretty dry basement.
Thanks for any help / guidance.
Rob
@ Rob – Thanks for stopping by the site.
1. Vapor barrier is tricky in basements. You’re not only trying to keep moisture from the concrete wall at bay but also moisture from the conditioned space from moving towards the cold concrete wall and condensing. If you use at least 1-1/2 inches of foam board, properly sealed I think you can avoid the vapor barrier. If not, the you may want to consider using it. If you use R11 to R13 you’ll be in pretty good shape. Some really cold areas end up needing more based on computer analysis.
2. If you’re saying that the fiberglass is exposed, front and back, and you plan on leaving it that way they fine. If you want to cover it up I’d be very cautious that you could end up with a moisture/mold problem. Eventually you’ll need to remove it if you’re planning on drywalling the wall. Make sense?
This Website gets 5 Stars from me! I am in North East Ohio and am stuck with oil heat. The advice listed here should help me save a lot of money. I cannot thank you enough.
I found this site recently and have to say it is great! Currently my basement in upstate NY is framed out with about a 2 1/2 inch gap between the concrete and the wall, with batting between the studs and foil covering the interior of the walls (no sheet rock).
I want to install the XPS board against my poured concrete basement wall, but my basement wall has little 1 inch nubs (looks like concrete encased steal) of where I think the forms for the basement wall hooked into when poured. Should I hollow out the XPS board to accommodate these nubs to allow the board to sit flat? Or because of these little nubs do I have to find a different means of insulating my walls.
Thanks for the help,
Jason
@ Jason – Thanks for the kind words!
Those nubs are created by small holes in the forms where steel ties hold the forms together until the concrete cures. You can either grind the nubs off using an Angle Grinder or you can hollow out the foam. I personally would just grind them off. Don’t worry about the steel, it’s just a non-structural tie used for the forming process. Good luck.
Todd,
Mike again. Another question.
In my walkout basement, what do I use to insulate the wood framing? Do I used unfaced fiberglass and install a plastic vapor barrier on the conditioned side or kraft-faced insulation and staple the edges to the framing on the conditioned side? Right now I have kraft-faceed unstapled fiberglass insulation and in a few locations I feel dampness next to the wall. Again, I am located in KY. and it does get fairly cold in the winter.
Thanks in advance for your help.
@ Mike – If you’re not going on put up drywall right away and finish it and paint it then I recommend you install fiberglass followed by a layer of poly. You need to tape all the seems really well.
Thanks for the quick response, Todd. I have learned a lot by reading you comments. Thanks for sharing your knowledge! Have a godd New Year in 2010!
Great info here!
I have the latest Black and Decker “Finishing Basements” book and I’m pretty sure that after they do the 2″ foam they do not show them using any insulation between the stud wall members. Is the fiberglass insulation between the studs optional? Or would you always do it no matter what?
Also, would you recommend the same insulating process for walls that are not outside walls? For example, in the basement room we are starting to finish two of the walls are outside walls but two of the walls are inner walls (concrete block separating two unfinished rooms on either side of the room we are finishing). Or would you use something else?
Thanks!
@ John – Thank for the compliment.
The fiberglass is optional if you need a higher total R value depending on your local building/energy code requirements. In some locations the 2″ of foam will be sufficient and in some areas it’s not enough.
As far as the interior walls I think you’d be fine not insulating them if they are surrounded by conditioned space on both sides.
Good luck.
I see, so if the recommendation for basements in New England is like R11 – R19 and you’re only getting R7 out of the XPS then you may want to throw in the between stud insulation to get up into the recommended rating?
Last question for today (and I’m sure this has been answered on this awesome site which I have now clicked and read about 10 articles from and learned more than i have in the last 3 months of searching around the Internet) if we do go with fiberglass batts between the studs would we go with faced batts or UNfaced? I have been reading that faced batts are usually used in basements since they Kraft paper acts as some sort of vapor barrier–but I didn’t know if that was actually going to be a *bad* thing if you’ve already got a sort of vapor barrier with the XPS?
@ John – Here in NH we have an energy code that actually requires an analysis of the building’s insulation envelope. So it’s hard to say what the exact number is until you analyze the building. Having said that you are correct, using a combination of foam and fiberglass is cheaper than just hiring a spray foam contractor.
The vapor barrier issue is not as cut and dry. If you’re installing 2 inches of foam and you tape it really well then you can do without the kraft faced….however,….you could use it if you like…as I doubt it will be a problem. The foam is thick enough to create a very good vapor barrier.
Thanks for all the nice compliments.
I have put up 1″ XPS on wall. Should have done 2″. Is it okay to continue w/ original plan of 1″ XPS – 2×4 wall w/ unfaced fiberglass – 1/2″ drywall OR should i overlay another 1″ XPS? I dont want the expense of the XPS, but I want to do this properly.
Thanks.
@ ChrisNE – It partly depends on where you live. If you live in a really cold area I say spend the money on more foam…if you live in the mid-atlantic for example you might be ok.
Thanks for your reply.
I am in Omaha, Nebraska which is pretty moderate normally. That said, in the next few days we are expecting high temps below zero and low temps of -15 to -20 below. I’d like to think I’d be okay as well. But sometimes that leads to trouble.
I think I’ll go with the foam. I’ve read that the fiberglass can trap moisture etc. I just don’t want to redo it. Building something properly means taking your time and making the right investment. Bah.
@ ChrisNE – Good decision! :)
[...] Insulating – Todd covers a variety of topics in this category and it is probably his most viewed topic. [...]
Great website! Great articles! I think I’ve read each article multiple times over, and even more so the comments section. What I haven’t come across yet are cinder blocks.
I am about to insulate my below-grade NY basement and I have a couple of questions. First off, let me say that I am more concerned about moisture and mold than heat-loss/insulating.
I was planning on adhering 2 inch form board (r-10) to my cinder block walls and then just studding out the rest of the basement. I was not planning on adding any fiberglass insulation unless it is a must. I am also leaving a 1/4 inch gap between the wood studs and the foam board because my sub floor is Dricore and they require an air gap.
Here is my problem: Will the channels created by the stacking of cinder blocks affect the development of moisture and the effectiveness/adherence of the foam boards?
Secondly, the Dricore was installed prior to the insulation. Therefore the foam boards will need to be placed on top of the Dricore flooring panels and not directly on the concrete floor. Speaking to a Dricore rep, they simply state that I should leave a 1/4 inch gap between the bottom of the foam board and the top of the Dricore panel. While this is great for airflow, will it create any problems? Everything I read states to seal, seal, seal.
Any help would be very much appreciated…
Thank you in advance!
@ Marc – Thanks for the compliments. At some point I need to revise the articles to incorporate many of the questions and answers that have developed!
There really is no difference at all between your block wall and a cast-in-place concrete foundation wall. Also, with 2 inches of foam you really have a good amount of insulation and fiberglass isn’t really necessary unless you local energy code requires a higher R value.
As far as the dricore…..I’m really not sure. I guess I’d follow their recommendation so long as you don’t put any fiberglass in the stud wall. As I’ve said over and over…BASEMENTS ARE TOUGH! Good luck.
I have learned a lot from reading this site! I am interviewing contractors for our basement build-out in Atlanta . I have asked them questions regarding insulating and subfloor options. Every builder has a different answer. We have a 4 year old house and have been blessed with zero water leakage or evidence of excessive moisture. I went as far to place a 12in by 12in piece of aluminum foil sealed with duct tape on the only wall below grade and the floor and had no moisture underneath after 48hrs. With all that being said, I have the following questions:
1. Would you moisture proof concrete walls with a sodium silicate like product?
2. Closed Cell Spray versus foam board?
3. If foam board, so much is written how fiber glass will become moisture soaked, so is the extra R value worth possible mold?
4. How are walls insulated that are both concrete and brick, 2 of our walls are both and the back wall is all brick…
5. What do recommend for a subfloor, we are leaning toward a cork floor?
Thank you in advance!
@ Chuck – Thanks for stopping by.
1. I honestly don’t think it’s absolutely necessary. However, if you’re the conservative type that likes a “belt and suspender” type of approach then it can’t hurt.
2. Closed cell spray is absolutely the better choice but it carries a much higher price and it’s not a DIY project.
3. You don’t have to use fiberglass. In fact, where you live in the south you’d certainly be ok using just a layer of foam board. Up here in the north the building codes sometimes require much higher total R values and the fiberglass becomes a cheaper approach.
4. Should be no difference between concrete and brick.
5. The sub-floor really depends on floor type and whether you want to insulate the floor. I would imagine you can get away without insulating the floor that far south. I would recommend you check with your flooring folks to see what is best for your concrete slab.
Good luck!
I have reviewed the site and appreciate the thorough coverage of the topic.
I live in central PA, temps between 15-90 through the year, I am in the process of finishing my basement. I live in a 3 year old house with poured concrete walls. I finished a portion of the basement to include a 1 inch air gap and fiberglass with vapor barrier to the walls. I applied drylok to the walls prior to framing. I am in the process of finishing off the rest of the basement and have continual concerns with the moisture issues (none known as of now). I have budgetary concerns, so I would like an economical solution.
I was wondering if I could….
Apply 1 inch foam, stud wall directly against the foam, with r13 fiberglass with faced toward room (noting the foam insulation would touch the fiberglass), or should I retain a 1 inch gap in the walls between the two insulations (you mentioned above regarding the thinner foam might condense water). Or would your recommend the 1.5 minimum foam with a fiberglass batt directly thereon. ( I would prefer the 1 inch to save on both cost and space).
Since I live in the mid atlantic, would a simple air-gap prevent the wicking of water, or is in your opinion the foam a necessity.
@ Dave – Thanks for stopping by. First off if it was my home I’d definitely install the foam. Most publications and research indicate that you really need 1.5 inches of XPS to create a vapor barrier. 1.5 inches of XPS will give you about R7 to R8 which is pretty good. Depending on what your local energy code says you might be ok with just that. You could always frame the wall with 2×3 to save on room.
Hope that helps.
Thanks Todd, I am going to do the XPS, but have some further questions.
If I were to place 1.5 inch XPS directly against concrete foundation, would you recommend not having drylok on the walls. In other words, can I save on drylok and put up a thicker XPS instead.
Also, if the 1.5 inch XPS would be a vapor barrier, will I run into problems with a double vapor barrier with faced fiberglass.
Finally, what are your thoughts on the air-gap between the fiberglass and the foam, would this provide the added protection against wicking.
Dave
@ Dave –
1. I say skip the Drylok
2. This is a tough question….if you have 2 inches of foam then there’s no need at all for the vapor barrier. With 1.5 inches you really can skip the vapor barrier if you plan on installing the drywall right off, taping and sealing it. Properly taped, sealed and primed drywall acts a good vapor inhibitor. There is no perfect answer for this situation.
3. The air gap is definitely a good thing.
Hello I live in New England Im remodeling our basement. I recently placed 1/2 extruded polystyrene rigid foam(DOW) as a first step to insulate my basement. I glued the foam board to the concrete and sealed every gap with tyvek tape and sprayed great stuff to the bottom and top of concrete. I know you have been saying 1.5 is ideal but it did not fall into the budget. Is the 1/2 foam good enough as a vapor barrier? Im worried i did the wrong thing. Should I use a R13/R15 faced or unfaced fiberglass insulation? I was told to stay away from using a 6mil plastic. I do plan on using 1/2 sheetrock to finish the walls
Thanks in Advance
@ Pete – 1/2″ foam will not provide a sufficient vapor barrier. If it were my house I’d install an additional layer.
A additional layer of foam? What if i used R13 faced insulation?I dont think i have enough space for exra foam
@ Pete – The trouble is having a vapor barrier at the concrete surface. There is a TON of moisture that comes from the concrete. If you don’t have room then put another layer of foam between the studs.
there is a lot of water it flooded my house
Todd,
Mike again. Another question.
What is your recommendation for insulating rim joists and the joist area against the outside wall? Do you also recommend XPS (2″) sealed around the edges with Great Stuff? Is there a code issue with unprotected XPS? I have unfaced fiberglass now-that is the way the house was built.
Thanks in advance for your answer. Again, great website and we all appreciate your help for us DIY’s!
@ Mike – I like to use 2″ thick foil faced polyiso foam board. I’m in the process of replacing my fiberglass rim joist insulation with it and I’ll be writing an article on it at some point.
Thanks for the quick response again, Todd. Looking forward to the new article about it. Will the article be located at this site or somewhere else? Please keep us posted where it is. I’ll wait for your article before doing anything.
@ Mike – It will be here. Subscribe to the email feed on the home page and you’ll get each article emailed to you. We’re just waiting to hear from some project sponsors before we begin.
Thanks
Todd,
Mike again.Have you had a chance to complete the rim joist article and if so how can I get to it?
Thanks.
@ Mike – Not yet. It’s quite easy though. I recommend you buy 2″ thick foam, cut it so that it fits between the joists, then use a can of Great Stuff foam to seal around all the edges.
Long story short – I live in a split-level and the downstairs is half-way under ground on the front side and above ground in the back. Due to a previous flood, I have found that I now have black mold under my sheetrock – even though “clean up” was performed. I began by removing 5′ of sheetrock from the ground up. I now have new problems. The walls are concrete block construction. No sealant – furring strips nailed to block (flat side against block) – and sheetrock nailed to furring strips. The strips are 1 X 2′s. NO INSULATION. Also, there is a furring strip laid flat against the floor (concrete) around the perimeter of the room. I am a single Mom and ripping everything out and beginning over again is out of the question. Outside of start over, what is the best way for me to insulate this area? By the way, the furring strips are not 16″ on center. I keep researching various sites – but just have no idea what to do. Well, other than lighting a match ; > I appreciate any suggestions you may have.
@ Tami – Unfortunately I really don’t think there is any other option. First off you need to get all the contaminated materials out of there as soon as possible. You should be very cautious removing it yourself as mold spores can easily get airborne and cause a serious health issue. There are lots of online government resources about proper mold removal. Once the mold is removed the best option is insulating the walls with some sort of foam board or spray foam.
Thank you Todd for your quick response. Yes, I have researched the mold removal and am in that process now. Once I have everything out (sheetrock and mold), would it be sufficient to glue the blue board between the furring strips and then sheetrock on top of that?
@ Tami – I would glue the foam board directly over the furring strips, marking the location of the furring strips, then securing the sheetrock over all that.
Thank you, Todd. Your website is priceless – and so are you!
Todd:
I have poured concrete walls in my basement. I used a combination of UGL Latext Dry-Lock paint and Super Thoroseal to seal out the moisture. I am now planning on gluing foam insulation boards to the painted walls. After that, I plan to build a framed wall leaving a 1-inch space between the insulation and the framed wall. Does this sound OK to you?
@ Dan – Sounds good, just remember to seal the foam well.
We just added more foam between our studs which brings us to a 1 ½ of sheathing. By adding this extra foam we only have 3 inches of space in some spots to put our R13 faced batts. Will it hurt if we stuff the R13 into a space that’s only 3 inches deep?
@ Rob – Fiberglass isn’t very effective when it’s compressed. You’re better off peeling it apart to make it thinner.
Does it matter if the fiber glass touches the foam or do i leave a gap?
Thanks for all your help!!
It can touch so long as you’ve sealed the foam well.
Really like your comments about basement insulation which I’m doing now: Foam board then stud walls and fiberglass.
My question is do you put tape at the bottom of the foam board where it contacts the basement floor? How about the top? I have already done the joints but there is air space at the top and bottom of the foam board. Thanks
Dennis – We typically fill those spaces with spray foam (Great Stuff).
Would Dow Super-Tuff polyisocyanurate foam core be acceptable to use in place of extruded polystyrene? Locally I can get it in 1-3/8 thickness with an R value of 8.3. I was looking for 4×8 sheets of extruded polystyrene but have only found 2×8 sheets. The 4×8 sheets will be a little more difficult to work with but I felt the trade-off was worth fewer joints to tape and seal. The price of the SuperTuff is almost the same as extruded polystyrene.
@ Jim – It’s a great product as well!
Thanks Todd. The front walls of my basement are completely below grade and the ground slopes towards the back of the house and the back walls are completely above ground. You recommend 1-1/2″ XPS with an R 7.5. I was thinking about using 1″ thick Super Tuff (with R 6.5) on the below grade walls and 2″ on the exposed walls. Will this be sufficient for the walls below grade? In addition to the foam there will be a 2×4 stud wall with R13 unfaced fiberglass.
Jim – The big problem is creating a good vapor barrier. 1″ just isn’t sufficient in my opinion.
Thanks again. One thing I forgot to ask earlier is whether there are any advantages to using XPS over Super Tuff. From an R value perspective it seems Super Tuff is the way to go. But you use XPS in all of your articles.
Jim – Polyiso has traditionally been found more often in commercial applications and it is usually more money. However, today it’s starting to show up more and more on residential projects. You can read more about the differences here: http://www.homeconstructionimprovement.com/foam-board-insulation-values/
I say both are good.
Above Dan asked about using “…a combination of UGL Latext Dry-Lock paint and Super Thoroseal to seal out the moisture.” before putting up foam board insulation. Is it worth sealing the concrete like this before installing the foam board? Also you earlier mentioned using polysio in the rim joist area. Is foil-faced polysio acceptable to have there uncovered?
Jim – I’m really not sure sealing the concrete will make much difference if you’re using foam. Not sure what you mean? Do you mean uncovered as if it’s a fire problem? All foam should be protected by some type of fire break like drywall.
I want to add insulation between the ends of the floor joists. In the area between the top of stud wall and the plywood for the flooring on the first floor. My basement has Kraft faced 3-1/2″ fiberglass insulation stuffed in there now. There was a hole in the garage where mice were able to get in the basement and they made nests in most of the fiberglass insulation. I plugged the hole about two years ago and have had no mice since. I want to replace all the fiberglass and thought about doing it with rectangles of foil faced Polyiso cut to fit between the floor joists and pressed up against the rim joist. I was wondering if the foil faced Polysio does not require a fire block like drywall if I use it in this area. You mentioned writing an article about doing this above, but don’t say if you are covering the 2″ thick foil faced polyiso foam board:
Mike says:
January 29, 2010 at 2:15 am
Todd,
Mike again. Another question.
What is your recommendation for insulating rim joists and the joist area against the outside wall? Do you also recommend XPS (2″) sealed around the edges with Great Stuff? Is there a code issue with unprotected XPS? I have unfaced fiberglass now-that is the way the house was built.
Thanks in advance for your answer. Again, great website and we all appreciate your help for us DIY’s!
Reply to this comment »
Todd says:
January 29, 2010 at 6:20 am
@ Mike – I like to use 2″ thick foil faced polyiso foam board. I’m in the process of replacing my fiberglass rim joist insulation with it and I’ll be writing an article on it at some point.
Jim – I haven’t written that article yet as I haven’t finished that project yet. I will at some point drywall my ceiling so the foam will be “covered”.
Thanks again. I was wondering because in another article on basement ceilings you seemed like you were going with a drop ceiling.
Also, I have two hairling cracks in the poured concrete walls. When we get a good rain a little moisture seeps in. On the one crack the concrete just gets a little darker due to the moisture. On the other a little water will run down the wall. Never more than just a drip here and there. Is polyurethane injection the best way to fix these? From what I read they seem like shrinkage cracks as they are close to the center of the wall and I can see them on both the inside and outside. My house was built in 1987.
Jim – the best way to fix cracks is with pressure injected epoxy. You could try the other but I’m not sure how effective it will be.
I have a basement that used to be prone to water. I just spent a lot of money with basement systems to put an interior french drain. The lip extends out of the floor-wall joint to catch any additional water coming down from the walls. The back wall is full height concrete, the front wall is half-height that extends a few inches out of the ground. The front-wall has standard framing, windows and batt insulation above the concrete.
How should I finish the basement? I was thinking of building interior walls 4 inches off the exterior concrete walls so they can “breath” and to allow me to see behind the walls.
I want to use metal studs with mold resistant building products. What do you recommend?
Mike – For starters I’m glad to hear you’ve addressed the water problem. Was all the work limited to the inside of the basement or did you make changes outside the house as well? I ask this because it’s important to know whether you’ve stopped water from coming in the basement or merely helped direct it into a drain. Do you still get signs of water? If you still have water I would be quite cautious about finishing the basement due to the extreme moisture that you will continue to have even if there is no standing water.
Having said that I would stick to ONLY foam based insulation products and preferably closed-cell foam. I would attach foam to the basement walls and seal the joints well. Then your idea of framing with metal studs out 4″ from that sounds like a good option. I would recommend you install the metal stud walls on top of a piece of composite decking to get the metal up off the concrete floor.
We did do some work outside with grading and extended downspouts. However, the water table is high here so water will always find my sump pits eventually. With a humidifier running in the summer I have no problem keeping the humidity level below 50%.
I would love to find an inorganic wall panel attached to closed-cell insulation that I could remove as necessary. However, they don’t appear available for DIYers. If I decided to just use closed-cell between the metal studs how would I secure it. Thanks for all the great advice!
Mike – You can secure it with spray foam from a can.
Todd,
Mike again – another question.
I have a bathroom in the basement (located against the outside wall). Is there anything special to insulating a bathroom? By this, I mean do I use unfaced insulation in the stud cavities with a poly moisture barrier all around the bathroom or just go with the standard kraft paper insulation in the stud cavities? The basement is conditioned and I plan to insulated the entire bathroom for heat and sound.
Thanks again in advance for your advise. Also, great to see your rim joist article in my email! Do you use glue to glue the poly to the rim joist the same as XPS against basement walls? I don’t remember reading what you recommended to glue the material to the joist.
Mike – Sounds like your bathroom has one wall to the exterior (concrete or framed?) and three interior walls. The interior walls you can use either method. The exterior wall should be foam if it’s against the concrete.
Rim Joist – I actually don’t glue it to the rim joist, the Great Stuff spray foam holds it all in place nicely.
Todd,
I live in southern NH and plan to glue 1 7/8″ foil faced polyiso(R-12.2) to my poured concrete foundation, leave a 1/2″ gap and build a 2×3 wall in front of that. I find, however, when I put a straight edge to the wall that many sections bow slightly in the center leaving gaps where the seems are. Are these gaps going to be a problem? Polyiso doesn’t bend, so they’ll be slight gaps behind the insulation.
Bob – I suggest you fill the voids with spray foam like Great Stuff.
Todd,
Unfortunately, my basement framing went up before I read this and one of your other posts. So, I’d love suggestions on how to make the best of the situation. There is 3/8 foam insulation on the foundation walls (not enough space to add a whole lot more) over dry-lock. The house is about 2 years old, so the foundation prep is good (water-proofed and insulated outside, foundation drain, slab prep), and the soil drains incredibly well (sandy) and allows little hydrostatic pressure. We’ve never had an ounce of water, even as others around have flooded.
Again, based on where I’m at in the project, what would you suggest? I was planning on adding batt insulation before sheet rocking, but your thoughts are appreciated. Oh, and off-topic, any thoughts on QuietRock?
Thanks so much.
-Kurt-
Kurt – At this point I think I’d install 1-1/2 inch or 2 inch foam between stud bays and be done with it. If you do it this way be sure to seal the edges with spray foam from a can. Good luck.
Todd,
I have read several of your articles’ They are very helpful and I am about to start my basement project. I have a couple of questions I was wondering if you can help me with.
What type of adhesive do you attached the foam board with? and do you have to do anything special to hold it in place while it cures?
I looked into PL300 Foam Board Blue Construction Adhesive at Lowes, but it says
apply it to the foam board
Press foam board against wall
Remove and let it sit for 2-3 minutes
Press foam board against wall again and mechanicaly fasten to wall until the adhesive cures
I hope there is a better product that you are using that I do not have to mechanicaly fasten to the wall while is cures. If this is the only way, how do you hold it against the wall until it cures? (I do not like the idea of shooting more holes into the basement wall to hold the foam in place)
Thanks for your help.
Tom – That is how we used to do it. Now we use http://building.dow.com/na/en/products/sealants/gspwallfloor.htm which works very well and fast! Give that stuff a shot….you’ll be glad you did.
If you can’t find it at your lumber store you can buy it here
Wow, thanks for your help, that will make it a lot easier.
By the way is there a difference between the Dow extruded polystyrene (blue board) and the Owens corning (F150). For some reason the Pink stuff is alot cheaper in the stores by me.
Tom – No real difference between the big blue and the pink panther. Just be sure it’s also a closed cell polystyrene.
How much Great Stuff Wall & Floor would you use for a typical 4×8 sheet of xps? I’m wondering how to estimate the number of cans needed for an entire basement. And Do you recommend a specific “gun/applicator”? I know Dow makes applicators are they good enough quality for a DIY’er doing a basement foundation and rim joist install?
Steve – We just apply dabs at the corners and mid points so it goes pretty far. You can probably get 8 to 10 sheets from a can. Most applicators work fine, just be sure to be set up to do a bunch at once and clean as recommended. Sometimes they do get clogged.
Thanks, that helps. Would you use the Great Stuff Wall & Floor to seal around the edges of XPS at the rim joist, too. I’ve never used the stuff so I don’t know if that is practical. Or would you use Great Stuff foam? I assume the minimal expanding?
Steve – I would use the regular Great Stuff Foam….(not the minimal expansion). Go ahead and let it expand, won’t hurt anything.
OK. Thanks. I’ve always found I waste a lot of “gap filler” foam but maybe it is easier to control with a “Pro” applicator.
Todd, do you have any experience with the Lowes XPS? I believe it is manufactured by Pactive. Since it is a “rebadged” product I can’t tell for sure but it seems to compare to OC 250 (R10 for 2″, 25 PSI).
OC 250 is
Water absorption(% by volume max) C272 0.10
Water vapor permeance(perm max) E96 0.60
Lowes is
Water absorption(% by volume max) C272 0.10
Water vapor permeance(perm max) E96 0.8
Do you think it is a reasonable replacement for Dow/OC?
Steve – I would imagine it’s the same darn product just produced for Lowe’s. Each of the box stores has started having “their” own branded materials manufactured to help them with price comparison and price matching. I’d use it.
Todd, Can you tell me if you are able to remove a half empty foam or adhesive can from the PRO gun and not have it blow all over the place? I need to do some foaming but I currently have an adhesive can on my gun.
Thank you, Larry.
Larry – We only use those guns for the foam. Typically we never remove the can unless it’s empty and then we quickly clean it and install another. As far as I know you can remove a half full can but you need to get a new one on it after quickly cleaning or you might have trouble.
I thought you used GS “floor and wall” adhesive for applying the insulation. That stuff requires guns AFAIK.
Steve – I’ve used several products including Great Stuff Pro, floor and wall, and regular GS. Some of it requires a gun and some does not.
Based on contradictions in your comments here it was confusing…
what tape do you use for seams? I’ve read that housewrap tape (Tyvek) has questionable longevity on XPS.
Steve – We’ve always used Tyvek tape with no problems.
FYI, two things I’ve read on Tyvek and XPS.
Tyvek warns against the use of Tyvek tape for sealing seams in plywood, OSB, or XPS foam. “The tape is designed to stick to Tyvek wrap,” said Alan Hubbell, a residential marketing manager for Tyvek. “Plywood and foam will expand at different rates from the tape, and over time it will crinkle and wrinkle and pull off.”
Also, someone did a test and the Tyvek tape came off after 11 months.
Steve – Thanks for sharing. I’ve found that it does work very well. I know that in one application the tape has been installed for over 4 years and still looks new today (the basement is not yet finished).
Todd, according to Dow, “Great Stuff Floor and Wall” has an initial bond of 2 hours. You mentioned it was fast, that doesn’t sound fast. Do you really use that stuff with no mechanical fasteners? At 2 hours I’m imagining having to rig something up with multiple points of pressure to hold a foam board on.
Steve – We never have trouble with it. First off we almost always use Tongue and Groove foam board, and most of the time we stand the sheets vertically. The GS does create some “tack” so it holds fine.
Thanks. I’d like to use T&G sheets but I’ve found that 4×8 T&G is special order at ever building supply place and is ridiculously expensive and 2×8 OC T&G (at least from HD) is incredibly poorly milled. Tongues and grooves don’t match up and sheets are not milled straight causing large caps. So I’m using square edge.
I start this week.
Steve – Another option that works pretty well is to apply the adhesive to the panel and let it sit for a few minutes until it tacks up…then install it. I think you’ll be surprised at how well the sheets do stand up.
Good luck.
I plan to follow your procedures on insulating my masonry walled basement. I will be using DOW Super Tuff polysio foam board adhered to the wall, taping joints etc. I will then build conventional 2×4 walls and insulate with fiberglass and cover with wallboard. Two questions. Which side of the polysio should be adhered to the wall blue face or bright face? Also should I use faced or non faced fiberglass for the finish?
Jack – put the blue side towards the concrete. The other side works well as a radiant barrier. Depending on the thickness of the DOW board you may not need either…..or you may only need unfaced.
Thanks Todd, I already have a few pieces up with the blue face toward the air space. Since I will definately have room for and plan to install fiberglass in the 2×4 cavities and then 1/2″ wallboard do you think it is worth the trouble and expense to tear out the DOW and install it as you recommend? I was following DOWs instructions on their web site and they did not specify which side to adhere to the wall. I was reading about radiant barriers and thought I was probably doing it incorrectly.
Jack – It won’t really matter much. Typically you try to keep in warmth (in cold climates that is) so the radiant barrier will slightly improve keeping in warmth. No big deal.
Great article! Super helpful. My question is as follows. I live in Pittsburgh and will soon start a basement remodel (unfinished basement). My problem is that my basement (like many Pittsburgh basements) has Sandstone walls that are highly wavy, bumpy, etc…
I don’t think pressing them against the walls as shown above is an option as there is no flat part. What would you suggest? Finding a straight line outside the most protruding point and start from there? Would the cavities created in the wall void all benefits?
All answers and help are greatly appreciated!
Thanks
Dave
Dave – Voids behind are NOT a problem. The key is to seal all the joints. So, if you can get the adhesive to stick, and then tape and foam joints, holes, etc really well it will work just fine. Good luck.
Much appreciated. I’ll keep you posted.
Do you see any problems using Owens Corning Pink Foamular 150 XPS? Owens Corning offers 150 and 250 with the only difference I see is the crush resistance. The 150 has 15 psi crush resistance while the 250 has 25 psi. The DOW Styrofoam brand has 25 psi resistance. The Foamular 150 costs substantially less than the DOW or 250. I wouldn’t think going with the 150 would cause any problems. The 150 is more easily damaged but once installed it shouldn’t make any difference. As a comparison I was quoted $18.85 for a 4′ x 8′ sheet of 1-1/2″ thick foamular 150 vs $26.36 for the same sheet in DOW blue board. Does this sound like a reasonable quote? Thanks.
Jim – What is the difference in R value? The 15 psi vs 25 psi may not be different in R value but it may be different in how well it acts as a vapor barrier. I’d be curious if they have any vapor transmission values published.
On a document I looked at on the Owens Corning web site titled:
“ASTM C578, Types and Physical Properties for Foamular® Extruded Polystyrene”
They list the “Water vapor permeance of 1.00-in. (25.4-mm) thickness, max, perm (ng/Pa·s·m2)” as 1.5 for the 150 and 1.1 for the 250.
But if you go to the data sheets for the individual products (Foamular 150 and 250) the “Water Vapor Permeance (perm max)7 ASTM E 96″ is given as 1.1 for both 150 and 250. I’m not sure of the 1.5 on the ASTM document is a typo or not. I just sent a message to Owens Corning on their “Contact Us” page. I’ll let you know where the error is if they reply.
On the ASTM document the value given for Foamular 400, 600 and 1000 are all 1.1. Given this I’m inclined to believe the 1.5 is an error since the permeance doesn’t change with density for the 250 through 1000 Foamular products. Why would it change with the 150?
From the ASTM document they also give:
The “Density, min, lb/ft3 (kg/m3)” for 150 is 1.3 and for the 250 is 1.55.
The “Water absorption by total immersion, max, volume” is the same for both at 0.3. In fact, it’s the same for all products from 150 through 1000.
I hope I was able to convey this in words that makes sense this late at night. Is the “Water vapor permeance” what you were asking about when you asked about vapor transmission values?
I forgot to add that the R value for the Foamular 150 and 250 are the same at 5 per inch of thickness.
Jim – Looks like you should be good then!
So, are you saying as long as the water vapor permeance is the same the 150 is as good as the 250 in terms of acting as a vapor barrier?
Jim – Yeah…that was my only concern. If you were using it for insulating a floor then you’d want the higher compressive strength. Since you’re using it for walls it’s a non issue.
i made my own interior water drain system and have a 1\2 to 1″ gap around the floor to the wall so would i just sit the xps right on top of the gap.also the great stuff is that the expanding foam your talking about. thanks
charles – Yes and yes. Good luck.
I’m building a cabin in the woods and want to insulate the floor prior to putting down the sub-floor. My cabin sits on piers, the lowest height from the ground id 14″ and highest is 32″. I have 12″ beams and 10″ joist for a total of 21″ above the piers. I have an oppertunity buy some Polyiso board at a very good price. do you see any issue with moisture ??? or should I go with blueboard?
addtionally, I plan on spraying insulation to have a complete seal within a year or two.
Thanks,
Karl
Karl – Polyiso will perform well in that situation. We often times use foil faced polyiso on the bottom of elevated walk ways, building cantilevers, etc. Just be sure to seal the seems well.
Hi Guys,
I’m going to start a basement project. I have block walls. I’m thinking about using 1 1/2″ foam board and then put either metal or wood stud walls in front of that. Do you need to put insulation in the wall as well or only if you want a higher R-factor? Also do you put any sealant on the bottom where the foam will make contact with the floor? Thanks for your help. Dave
Dave – Additional insulation depends on the energy code where you live and what R factor you need. I prefer leaving the bottom loose so that water can drain if you get any behind the foam. Some folks choose to seal it and that’s ok unless you know that water gets back there.
Thanks Todd. Would the extra insulation be unfaced or would more foam be better. Also, when putting insulation on the basement ceiling would you just put unfaced fiberglass insulation? Thanks, Dave.
Dave – You can do either. If you can afford the foam then use it, otherwise you can use fiberglass. Just be VERY sure to seal all the joints in the foam very well.
Unfaced in the ceiling is fine.
Todd – A few people mentioned putting up foam board and leaving a gap between the foam board and the metal stud wall. Is this needed? And would it be any different with wood? Plus, have you ever used 2×3 metal studs? Space saver but is it as strong? Thanks, Dave
Dave – The gap is more important if you’re installing fiberglass in my opinion. If you’re not then I’d frame up tight against the foam. 2×3 studs could work but I’d be sure to get a heavier gauge if it’s available.
Thanks Todd, If I would use foam between the studs, would you glue it and try to stager the seams? And would you use the thin pink sill foam under your wall? Where the metal or wood make contact with the concrete floor? Thanks again for all your help.
Dave
Dave – You really want to get a good layer behind the framing and tape the seams. Once that layer is installed I’d cut pieces to fit between the studs, another 3/4″ to 1″ thick. Use spray foam from a can (Great Stuff or Great Stuff Pro) and seal the foam to the studs.
Todd, I am finishing half of a walkout basement in Alaska where about half of the walls are cement and the other half are 2X6 stud walls being the outside of the house. I just poured a concrete floor where there was sand and rock for the last 7 years. When I moved in the walls had fiberglass insulation hanging in strips and after pouring the floor I framed the walls with 2X6 studs and put the fiberglass strips in between the studs. I now see I should have put some kind of foam board behind the studs, but it is too late for that. Can I pull out the fiberglass insulation, cut 16″ strips of the foam board and add it against the cement walls, put the fiberglass back in, then put a plastic sheet over the whole thing and be good? I plan to put log slabs on these interior walls to make it look like the interior of a log cabin over that.
George
George – You can do that but it’s not likely to stop moisture problems. Basements are very difficult because moisture wants to travel in two directions depending on the time of year. In the winter warm moist air will move towards the cold walls, him them and condensate. In the summer the cool damp air along the concrete will want to move into the finished room, hit plastic and possibly condensate.
I say all this because the foam board serves two purposes, insulation and vapor barrier. By cutting it in strips and installing it between studs you end up with a broken barrier and broken thermal break. Hard to say what will result but it’s a good bet moisture will get through it.
Todd,
Ouch, thanks for the quick and candid response. would I be better off not putting the plastic on the inside then and possibly allowing the insulation to have access to the warm air from the room?
George
George – May sound like a lot of work but could you simply move the new walls? Many times walls are pretty easy to “cut loose”, cut the nails/bolts in the bottom plate, cut the nails up through the top, then move it out, install foam, put the wall back?
Short of that I’d stay with JUST foam and take your chances, seal it well.
OK, thanks very much Todd. We used a sledge hammer to get two of the walls to fit under the floor beams, so it is not coming out short of sawing it apart. I’ll “seal it well.” Once I put the foam in between the studs is there a compound you would recommend to seal up the cracks between the foam and the studs in order to get the good seal? Do you recommend glueing the foam to the concrete?
George
George – We love using Great Stuff Pro. It seals, adheres and works beautifully. Best of luck.
Have a quick question…. we are insulating our basement walls with foam sheet insulation. I think we are going to use the technique pictured above and tape the seems before we apply the studding. My question is, the walls were previously drywalled over paneling. We have stripped everything off and the studs were just cheap 1/2 boards that were mildewed. We pulled those off two. We have bleached down the walls and am wondering if we should paint on a layer of water sealant before we put on the foam insulation? Thanks much..
Sarah – It’s really not 100% necessary. If you install at least 1-1/2″ thickness of foam it will retard water vapor from coming through.
Todd, I love the site and your wiliness to answer our questions. Much much appreciated.
I am in the process of redoing my basement and had the pleasure of finding furring strips nailed into the walls. I really don’t want to start over so I think board is the way to go. My question is really two parts. First, should I add 1 1/2 inch board in-between the furring strips, or do I cover them up completely and start with a full seal? What about putting 1 1/2 in-between then another inch or so over the entire area? Never read about stacking the boards and if that is actually practical. Looking to get a good vapor barrier, good R-value, yet working around the furring strips as is. Much appreciated!
David – Thanks for stopping by and thanks for the nice words.
I would install a layer right over the furring strips. At a minimum I’d use 1-1/2 but preferably 2 inches. If you use 2 inch long screws with large fender washers that should do the trick. I’d be sure to use galvanized or stainless steel. Then when you’re finished I’d seal over those with tape as well. Then you can install drywall directly over the foam.
Good luck.
That sounds like a plan, just to follow up with few more questions. How would you handle the electrical – do they makes boxes that will come out 2 1/2 (foam and drywall)? and would I great stuff the tops where the gaps would be? Lastly how far off the floor would I go? Going to add a sub floor if that makes a difference.
David – You’ll have to get creative on the electrical. You might be able to find extension boxes that deep but I’m really not sure. I’d speak with an electrician for ideas that would meet code.
I’d cut strips for the top and foam them in place.
I’d drop the foam down to the floor.
Thanks Todd!! Now I just need to pick a product to use.
Super Tuff-R looks good, but I see you did not pick that product in the above pictures – any reason why? Any favorite? Tuff-R is a poly versus a XPS is what I gather from your article and research, but does it matter? Has a better R value…
At the big box stores today and the see adjustable electircal boxes – amazing what they have now a days.
Super Tuff-R is a great product as well. Any of those will work just fine.
just read the comments again, I see you like both.
As the others have said before, thank you for sharing your experience. I noticed the xps used to fill cavities between the floor joists is faced. Couldn’t un-faced be used as well if the lower walls and ceiling will be finished with gypsum board? Also, is insulating this area necessary with a continuous rim board (I no longer recall the thickness) and a brick structure?
Larry – Faced vs unfaced for xps depends on a couple things. First, foil faced works very good as a radiant barrier as well as insulating. Also, foil faced has a lower flame spread rating which is nice when it’s left exposed. So, you’re correct, in an application behind drywall the foil faced may be overkill.
As far as the rim board, this is an area that lots of folks don’t insulate and they pay the price. Insulating the rim board is one of the most effective solutions for cold floors. I wouldn’t skip it EVER!
Good luck.
Thank you and I plan heed the advice of experience.
We are going to close these comments because they have gotten so long. We would like everyone to move on over to the forums section and post their questions there.
http://www.homeconstructionimprovement.com/forum/insulation/basement-insulation/
Thanks in advance!
Hi Todd,
Websites that give remodel recipes are great. But being able to ask questions is extra great.
Here’s my situation. I’m going from unfinished to completely finished in my 1938 poured concrete basement. We live in Seattle where the ground is wetish 8 months or more. However, I’ve cured most of my major sources of flooding by redirecting downspouts and installing an internal french drain with a sump.
My plans for finishing are as follows. For the walls, I’m planning on putting up 1.5″ XPS with 2×3 framing over that with unfaced batts. For the floor, I’m planning on Delta FL + 1″ AdvanTech over the entire basement, and then complete with combination of tile and laminate. Even though I’m not getting the best insulation this way, I like the Delta vs ORVX because of the air gap and strong vapor barrior.
Ok great. Here are my two open questions:
1. Should I put walls on top of the subfloor, or put walls directly on the slab. Seems like walls on top of subfloor is easier to install (can nail to the OSB, lessens the baseplate rot hazards, and leaves more of a nailer for drywall and baseboards). However, if I ever need to pull up the OSB to dry out after a flood, I’ll be kicking myself for tucking the floor under the baseplates.
2. When the contractor installed the french drain, they talked me into extending their heavy dimple sheets all the up the wall. You’ve probably seen these, but for other readers’ benefit, before the concrete is poured back into the basement perimeter drain trench, 20 mil or so dimpled plastic sheets are layed over the french drain and extended continuously up the wall, and then tacked to the concrete walls with a zillion nails and plastic expanders. The theory is if water comes in somehow through the wall, it runs down and into the footer drains, never bothering the basement interior. Awesome idea I thought at the time. Now I am hearing that really you want your XPS right up against the concrete. So, my question is, should I remove and cut off the dimple sheet down to a couple inches above the slab (still want the drip trap) so the XPS can press flush to the concrete? Or, can I just install the XPS over the dimple sheets. My concern is that there is an air gap behind the sheets, and condensation will collect and perhaps undermine the effectiveness of the XPS.
Thanks in advance,
Geoff in Seattle
Geoff – Thanks for visiting the site and the nice compliments.
1. Most folks end up framing on top of the new sub-floor. You bring up an excellent point about what you’ll do if flooding happens again. I frankly don’t think it’s a huge deal because you could easily cut along the wall/sub-floor in the future and free it all pretty easily. I would just frame on top.
2. The only issue I see is whether or not you can get the xps to stick to the dimpled plastic. I think you probably can if you use something like Great Stuff Pro. If it will stick, just leave it, it won’t hurt anything and frankly I think it will provide a great air layer that helps things dry out.
Good luck…let us know how it works out!
Todd,
Thank you for a wonderful site. We are looking to finish our basement. We are in central Wisconsin and have a year old house, poured basement walls with 1 inch of blue, I assume xps, on the exterior. What do I need to do on the interior? I have seen this builder finish their basements with 2″ gap then 2/4 studded walls with batting.
Thanks,
Candace
Candace – I would NOT recommend that approach at all. I would recommend 2″ of foam, stud wall, then wall finish with NO batt insulation.
Thanks, that’s what I’ll do. Both building centers priced out with batts and friends I asked said batts, but your approach makes more sense to me. I have been in finished basements that smell mildewy and don’t want that. Thanks for your quick response. Blessings.
Hi Todd – I have a similar situation but further in the finishing. Exterior foam on basement walls, one year old poured basement – no signs of water. Here’s the kicker….basement wall framed in already with 2 by 4s. So…what options do I have that don’t involve moving the walls?
Thanks! Your site is great!
I would actually move the walls if it were my home. Moving the walls typically isn’t that big of a deal. Most walls can simply be cut free, slid forward and re-attached to the floor and framing above. If you don’t want to move the walls then I’d recommend spray foam. The last resort which I don’t like very much is installing foam between stud bays. However, the studs will be exposed to moisture on the foundation and likely deteriorate and mold over time.
We have a split-level home build in the 70′s and the family room is 1/2 below grade and 1/2 above. The walls above grade were insulated when it was built but the portion below grade were not. They get very cold in the winter and we even get a breeze below the baseboards! I would like to add insulation somehow but my husband is concerned about moisture since a plastic vapor barrier was probably not used before the studs went up. Is this something we need to be concerned with? Could we cut holes in the drywall between the studs and blow in insulation? Or should we remove the drywall completely and try to install some kind of a vapor barrier and then add regular insulation? I don’t want to freeze through another winter!! Thanks for any help you can give us! By the way, we live in a Chicago suburb.
Karen – You’re not alone in living with a cold drafty split level. It’s not uncommon to hear of split levels that were only half insulated for fear of moisture problems along the basement walls. If it were my home I’d consider one of two solutions.
1. Tear down all the drywall, remove the old insulation, then seal all the cracks, voids and possible draft locations with spray foam from a can. Then I would insulate the lower portions with a minimum of 1-1/2″ of closed cell foam board, edges sealed with spray foam. Then you can fill the remaining cavity with fiberglass above and below. Another alternative would be to use all foam board from the bottom up, probably want 2″ minimum or more for that scenario.
2. Cut the drywall horizontally at the transition from below grade to above grade. Remove the lower half of drywall, insulate with foam board, seal well, then install new drywall.
I would avoid blowing insulation into the lower cavity as you will have major moisture problems. Good luck.
Thanks Todd! I think we will be going with option #2. We had thought of that but my husband was still concerned about moisture at the stud seams. We hadn’t thought of using the spray foam to seal the boards! I can’t wait to feel the improvement this winter!
Hi Todd,
I think it’s great how many questions you answer and how many people you’re helping with your advice – thank you!
I am remodeling my basement. I have a installed, and have put down and ¾” T&G OSB on top of that. I’m going to put 2” XPS on the walls, and then frame a 2×4 wall just inside of that, on top of the Delta and OSB. I’m looking for advice on how to handle the area where the XPS meets the top of the drainage channel. I’m considering 3 options: 1) Bringing the XPS down to just above the channel, and leaving it at that. 2) Notching the XPS so it will fit down further over the channel, and sealing the front edge of the XPS to the front edge of the channel (I would also seal the edge of the Delta FL to the concrete in this case). 3) Sealing the bottom front edge of the XPS to the top edge of the Delta FL (may need a little poly to connect the two), to connect the airspace of the channel to the space under the Delta FL. I believe options 2 and 3 will both keep the moisture out of the wall cavity, but if there’s no reason to not go with option 1, that would be my first choice, as it’s the easiest. What would you recommend doing?
Thank you very much!
Jason
Sorry – links didn’t work. Squidgee Dry is the baseboard channel – http://www.waterproof.com/installation.html
And Delta FL – http://www.cosella-dorken.com/bvf-ca-en/products/foundation_residential/floor/products/fl.php
Thanks again!
Jason
That first sentence is supposed to read as follows:
I have a baseboard drainage channel system installed, and have put down Delta FL and ¾” T&G OSB on top of that.
Jason
Jason – Thanks for the kind words.
Couple questions.
1. Where does the “baseboard channel” system drain to? Is it connected to a sump or something?
2. Has your basement ever flooded?
3. What part of the country do you live in?
Your questions all revolve around how far to seal this and if you do where will the water, vapor barrier go. I would seal things up real well if that channel is connected to some sort of drain. If it’s not connected to anything then the question still remains as to where the water will go if you get an event.
How “deep” is the channel? Could you use a thinner piece of foam board in front of that so it’s easier?
Interesting system you’ve got!
Hi Todd,
The baseboard channel system does drain to a sump pit (forgot to mention that). I’m in St Paul, MN. The basement has never flooded. Just to be safe though, I’ve recently installed a ~2′ deep french drain on the exterior of the uphill side of the house to channel away surface runoff water. I also re-graded around the house and extended the downspouts. We’ve had some pretty heavy rain this late summer/fall, and while the sump does run a bit, we’ve gotten no water in the basement at all.
The channel is 5 1/2″ tall, with about 4 1/2″ of it above the Detla FL / OSB. It sticks out just less than 2″ from the wall. There is only about a 1/4″-3/8″ gap between the OSB and the channel. It sounds like you think I should seal it up to keep the moisture out of the wall cavity. XPS will let some water vapor through into the cavity anyway right?
If I seal the 2″ XPS to the front of the channel, would you seal the back of the XPS to the wall, so no moisture could get up behind the XPS, or would you leave it open so any condensation could drain down into the channel? I’m not sure that there’s much benefit to trying to keep a connection between the space in the channel and that under the Delta FL, so I’ll probably seal both independently. Let me know what you think – thanks again!
Here’s a pic that may help visualize everything:
Jason
Ugh – I’m horrible with the links – My name links to a drawing on flickr of what I’m trying to describe. Thanks!
Jason – The real key is keeping moisture from the wall framing not the concrete or block. So yes, seal anyplace where vapor can get into your framing but don’t worry about the concrete/foundation side.
Todd,
Great website! I am planning to finish my basement, and have a question about insulating the top of the poured concrete walls.
I will install blue board from the basement floor to the top of the concrete wall, but there will be a small portion of the wall that will be exposed (where the treated plate sits on the sill seal). The treated plate on top of the poured wall is a 2×4, and the concrete wall is 8″ thick. Should I cover the exposed portion on top of the wall with some insulation, or not worry about it?
I have some “half walls” as well that will need the same treatment.
Thanks!
Michael
Michael – Thank you for the compliment. Cut a strip of the foam the width of the remaining concrete, foam it into place along both sides.
Hi Todd,
I’m planning to insulate the walls in my basement that is basically a 4 1/2′ cement floor crawl space. I’m going to use 4X8 foam as you suggested and cover the top of the wall to rim board also with foam board.
-I have no isssues with moisture on the walls, can I glue/seal the board on the bottom also?
- I dont plan on drywalling since it will nover be a living space, but am thinking I should do something for fire resistance. Would applying a coat of latex or drylock over the foam board work ok?
- would white styrofoam board with a foil cover on one side be suitable?
Jim – I’d use foil faced polyiso foam board and be done with it. It costs a bit more but it’s really the right product for that situation. You can seal the bottom, won’t hurt anything.
Good luck.
Thanks! I think it is really good to have a webform such as this. Keep up the good work!
Todd,
I have a suspended concrete garage floor over a basement storage area. The garage above is insulated but not heated. I’d like to insulate the bottom of the garage floor to keep the basement warmer. What would you recommend?
Thanks for the great site — I think it is the best info on the web!
Tom
Tom – I’d probably consider one of two approaches.
1. Attach metal z furring to the concrete then spray foam. The Z furring would allow you to finish the ceiling with drywall or some other product.
2. Attach foil faced polyiso insulation to the ceiling with some type of fastening system.
Good luck and thanks for the kind words
Todd,
Awesome site. Thank God for google. I’m finishing off my basement (walls are concrete block below grade), however, I have a support wall running down the middle of my basement and a room (~ 1/4 of my basement square footage) that is pretty much partitioned off from the rest of the basement, half by block and the other half by a studded wall. Inside this room, I’ve got shelving that would make it impossible to insulate the walls. Connected to this room is an addition with ~3′ of crawl space and two big openings from the crawl space to the basement. What would be your recommendations for this storage room and the crawl space (concrete block also) that is connected to it?
Thanks,
John C.
John – Thanks for the compliment.
Sounds like you have an interesting situation. Without knowing many of the details it seems as though you may want to approach this as two separate spaces. You can properly insulate the new space and you can insulate between the new and the old.
Then you’ve got the “storage space and crawl space” to deal with. Crawl spaces are typically even more complicated to deal with depending on the type of floor. If you have a concrete slab it’s not all that different to a normal basement. However, if you have a dirt floor in there then you’ve got a really tricky situation.
I guess the first question is will the storage space and crawl space be heated? What type of floor is in there? Is there any ventilation? With some more basic information I might be able to point you in the right direction.
Todd,
Thanks for the prompt response. The crawl space has a concrete floor. I have a fairly tight house, spray foam in first floor. Because the crawl space was connected to the basement with two holes about 3 x 3′, I decided to foam up the crawl space vents. I’ve debated about sealing the holes between the two spaces. Their is insulation in the joists in the crawl space.
Cheers,
John
John – I would probably focus on insulating the “floor” (under side of joists) really well in the crawl space and leaving that space as an unfinished area. Foil faced poly iso works really great in that application. That should help with the warmth of the floor above. Then insulate the wall between the finished space and storage areas really well.
Hey Todd,
I’m so glad to have found this site before I get any further into my basement project. I have painted the concrete walls with DryLoc and that is it so far. I was going to do everything very differently before I found this site, but now my main question is…how do you tie the stud wall to the foam covered concrete block wall? OR, do you not bother to do that at all? I have three and 1/2 walls to insulate and drywall. The fourth wall and half of one of the adjacent walls are interior stick-framed walls. Do I tie my stud walls to the basement floor and overhead floor joists (with bottom and top plates) only or do I try to anchor to the block wall somehow? My plan was just to put furring strips atop the foam, but if I use 2″ xps, then the screws would have to be mighty long. Same with the floor. If I use 2″ foam, do I have to use very long screws to get through the foam to secure the sleepers to the concrete? Hope I hear from you in time to buy this stuff for a 2010 tax credit! Thanks a million! em
Elizabeth – Thanks for visiting the site.
1. There’s no need to attach the walls to the foundation wall. Typically the framed walls will be attached to the slab and to the joists above. In fact, many times we’ll leave a small space between the foam and the framing.
2. I see you posted another comment on the floor article so I’ll respond to the floor there.
Good luck!
Hi Todd,
Do you see any problems with this type of installation for my basement: ?
4 Mil Plastic Sheeting over the poured concrete wall, then a PT 2×4 on the floor and KD 2×4 at the ceiling with 3 1/2″ of PolyIso Foam Board (2 1/2″ Board and then a 1″ Board) in between. The poly iso would be attached with furring strips OR 2×3′s layed flat over the top and Tapcon’d to the wall. Should I spray foam or seal tape the seams still, or not necessary with the plastic vapor barrier on the wall? I then would attach my sheetrock to the furring.
Having 3 1/2″ of Foam I didn’t see the need to buy all of the studs to frame out a wall in front since I would not be using Fiberglass Insulation.
Thanks.
Jeremy – Interesting approach. It will likely work ok but it does have some “risks” as you’re driving Tapcon’s through the PolyIso. Overall I think it’s a decent system that will likely serve you well.
Hi Todd,
GREAT site, thanks for all the wall and floor insulation and sealing tips.
To line the inside of my (poured concrete) basement walls, I plan to follow you advice and use the 1-1/2″ XPS board; however, in my area the DOW-made XPS product is very hard to get and its really expensive. Would the Owens Corning FOAMULAR® 150 or 250 pinkboard be a worthy substitute? its half the price.
Also, as I have some drylock sealer, would it help to help seal the walls/floor to put this on first before adding the XPS?
Thanks for your help.
Cheers, David
David – The brand really doesn’t matter, you just want to be sure it’s a closed cell, XPS type foam. I consider the use fo Drylock sealer a belt and suspenders approach. Not really us it is worth the effort IMHO.
Todd,
Very informative web site. I live in VT. I see that you are in NH. You undoubtedly know of some of the challenges with New England construction. Thanks for taking the time to provide your professional opinon and input.
In a recent December rain storm I had some basement flooding (appox 1″) due to blockage in my perimeter drain. The drain has been cleared/jetted and I have been monitoring the daylight end to insure it does not get blocked. There is a constan slow trickle of water. There have been two additional periods of heavy rain as well a thaw/melt of approx 6-8″ of snow over the New Year preiod. I have seen no additional water so I believe that problem has been resolved. In the spring I plan on having a complete inspection (and cleaning/repair as necessary). This was the first time in 11 years that I have had any problems with water.
I plan on using your foam board technique on the uninsulated (poured concrete) walls. My question is this, should I place the foam board directly on the slab or hold it off the slab (3/4″ or 1.5″) to allow easier water egress if there should be any future events.
Thanks again for your valued comments. I’ll be book marking this site and signing up as a Facebook friend.
JohnE
John – Thanks for the compliment neighbor!
Now that you’ve had a water “event” it probably makes sense to hold it up just a tad, 1/8″ would be more than enough. While I’m not sure the foam down on the slab would stop the water it is best to give it a clear path so it’s not trapped back there.
As added insurance you may want to consider a sump pit/pump in case this happens again in the future.
Good luck!
Todd,
Thanks for the input. I did do some additional reading in the forum area and found someone there with a similar situation as well as similar advice. At this point I am trying to get the plan and materials together. I’m want to wait until after mud season before going crazy with the work. Not point on getting it all finished only to have a reoccurance.
As I have not had a problem in the 11 years I’ve owned the property and previous owners did not mention problems I am assuming this may have been a one time occurance, especially since I did have a full blockage on the perimeter drain (daylight end plugged). BUT the sump pump idea has crossed my mind. Once water finds and easy path, you can be sure that it will seek the same path if a similar event happens in the future. I didn’t lose a lot but it was a enough of a pain that I want to insure it doesn’t happen again.
Do you have any recommendations for sites/info on basement drainage systems?
JohnE
John – We have a couple articles you can start with.
http://www.homeconstructionimprovement.com/fix-wet-basements/
http://www.homeconstructionimprovement.com/basement-sump-pumps/
Todd,
Looked at your articles and followed some of the links. Some of the photos showed some really bad water problems. My situation is not close to that. I honestly think that my problem was the exterior foundation drain being blocked. Also all my down spouts did not direct the water away and two of them disappeared under the deck. I have not yet checked but my thought is that there is a strong possibility that they were tied into the foundation drainage system. A good drain cleaning and proper routing of gutters and down spouts will probably resolve the situation. A sump pump is probably good “insurance.”
Just over 1/2 my basements is already finished and that in 11 years there was nary a sign of water or moisture problems. A full interior drain system is somewhat impractical. My foundation is solid poured walls and a poured slab.
Would a sump hole provide enough hydrostatic relief such that an water build up against the walls/slab would find it’s way to the sump hole? What would be the best location for a sump hole? The lowest point in the grade of the basement floor? Close to that area that looks like the primary entry (judging from the water stains the occurred on the walls)? Or any convenient point close to a wall/corner?
Sorry for all the questions. I’m one of those do it right the first time guys (I don’t have the time or money to do it twice). I also know how important it is to have a full plan before stating a project.
John – It certainly sounds like you’ve fixed the problem. Many people decide not to install a full perimeter drain as it’s not always feasible. My thoughts are that you can install a sump hole with pump so that if a flooding situation happens there’s a place for the water to go, a way for the water to be removed and a way to prevent water from getting any deeper than a puddle. Obviously if there’s a low point in the slab you’d want to be near that.
I’m not sure that it will change the hydrostatic pressure enough to totally eliminate a problem in some situations. One classic flooding situation that we see is in the spring, after a very cold winter, deep frost, then a quick thaw, melting snow and rain. The frost prevents normal drainage paths and the water get’s trapped up against the foundation. That type of situation usually causes some flooding that normally would not occur. In that situation it’s not likely that a sump pit would change the hydraulics enough to prevent the flooding. However, if it did occur the damage would be limited by the sump.
make sense?
Todd,
Yes, it makes sense. I will find the low spot on the slab and will see what happens from there. Regardless, for the reasons you mention, I will not be starting any of the major portion until after the spring thaw/mud season.
Thanks for taking the time to help me and answer my questions. Your website is full of useful information. You can be sure I’ll be checking in from time to time and especially when I’m in the planning stages.
JohnE
Todd,
The people that owned our house before us put up Dow Super Tuff-R insulation, then framed the walls and hung drywall over that. We are doing a remodel and wondered if we should remove the Dow Super Tuff and completely start over, or should we just fill the cavities with unfaced fiberglass and re-drywall? The insulation they used is foil faced on the interior side and only about 1″ thick. Will this serve as a proper vapor barrier or will this create long term problems for us?
Any guidance would be extremely appreciated.
Thanks,
Chad
Chad – Did they seal all the seams well? Some foil faced products are able to stop water vapor a bit better. I think if it’s sealed well then it might be ok. Instead of using fiberglass I’d use additional foam between the studs.
More foil faced or just another 1″ of xps? Do I just glue it tight to the foil face, does this just make the foil face obsolete?
Also, I’ve hunted through all you articles and comments and haven’t found anything about insulating partition walls. What is recommended for a partition wall between a heated/finished area and a unfinished/unheated area?
You are by far the most informative/ biggest help on the internet. I wish more people shared their knowledge like you do.
Thanks again
After continuing to read your articles, I’m really considering just tearing everything out and starting over with 2″ xps, followed by framing and unfaced insulation and then drywall. Is there any ideal place to reuse the foil faced foam?
Chad – Foil faced works great in exterior applications, under porches, crawl spaces, in garages, attics, lots of places.
Chad – I’d use XPS, glue it tight to the existing and seal the seams.
Partition walls can be insulated with fiberglass, vapor barrier on warm side. However, if it were my basement I’d use foam board for those as well.
Thanks for the compliments, glad I can help out. I hope you visit often!
Thanks for the quick response. Could I use the foil faced foam in the partition wall? Foil side on the heated side with unfaced fiberglass behind it to boost the R value? Would I need to keep the drywall out a 1/2″ from the foil faced or could I screw it tight to it? Would I still need a vapor barrier?
Chad – You could certainly use it for that application. I would put the foil on the warm side, then unfaced fiberglass.
Good luck.
Hi Todd,
I bought the rigid foam board, and went back to my local lumber yard for the tape to seal the gaps. After a conversation about what I was doing the salesman said I should stop immediately. He said using foam board directly against the basement wall will allow water to trap inside the concrete and crack my foundation. A little worried now and would love some advice.
Jason – All I can tell you is I’ve personally used this system with success and it’s also the system that is most recommended by Building Science.com http://www.buildingscience.com/documents/reports/rr-0308-renovating-your-basment/view?searchterm=basement
Furthermore almost all building codes now endorse the use of closed cell spray foam directly against foundation walls.
I don’t want to get into an argument here but the guy at the local lumber yard is wrong.
Hope that helps.
That does help and thank you. I went ahead and did it anyway. The reasoning is sound and I do have a very dry and cellar so I won’t worry about it. Thank you for all your posts and your quick replies. A great resource!
Jason
Also, not that it matters, but I was watching Holmes on Homes who does the exact same finishing as you do and I’m pretty sure most of his are filmed in Canada so a colder climate than what I have.
Thanks again.
Jason – Glad to help. I just saw Mike Holmes this week at the International Builder’s Show. Good guy!
Todd,
I’m getting ready to start insulating my basement walls with the extruded foam, etc.
My basement is quite large and I only intend to finish half of it for additional living space and leave the rest as storage. There will be a wall separating the the two sides. If I do a good job with foam etc. on the partition wall, do I still need to insulate the foundation wall of the unfinished side?
Stopping with the partition wall would save me quite a few $$$.
Currently, my entire basement has drylock on the walls and epoxy paint on the floor … but no vapor barrier or insulation.
thanks in advance for your help
Dan
Dan – That should be fine. Just be sure to insulate the partition wall well.
Good luck.
Todd
Our new home iS a 60 year old house. It has a cement block basement set on a raised concrete footing. The concrete footing rises visually above the basements concrete floor some 6 inches. Seeing that this footing extends 2 inches out from the base of the block wall itself, how would a person insulate the wall and footing all the way down to the concrete floor, and still get it securely sealed from the top of the block wall to the basement floor itself?
And how would one build the frameing of the wall to accomadate the 2 inch ledge by 6 inch drop, from the base of the block wall itself on down to the floor and over this protruding footing to proprely seal the whole wall from top to bottom?
Thanks Marve
Marvin – There are two options.
1. Let the foam follow the wall and footing. Cut it to fit and seal the seams well (the foam will follow the same shape when you’re finished.
2. Either frame a wall just in front of the footing up to the ceiling or frame the wall to follow the shape again. Just depends on what you want it to look like.
Thank you ever so much Todd. One more question.
Can a person use a foam board with alumanim reflective foil on both sides directly on the basement wall, or will it draw unwanted moisture?
Marvin – Typically we stay away from foil faced applied directly to concrete. You’re better off with regular XPS. The foil facing can react with the concrete.
Thank you Todd, you have been a great help to my project, and now I know not to use any foil faced insulation board with foil on both sides on a basement wall, and also why it shouldn’t be used.
Thanks again.
All the articles I’ve read say “seal the foam joints with tape”. If you are using something like great stuff in the joints why would you need to tape the joints? When doing the rim joist using rigid foam and great stuff, “one” doesn’t tape the joints do they ? – at least I’ve never seen it.
Steve – Yes…we seal the joints with tape (usually tongue and groove foam board so no spray foam). You are correct…90% of the time the rim joist is just foam as the pieces of foam board are small and not patched together.
My experience in my house given:
- limited access areas
- accessible areas with obstacles
- length of side joists
there are a many patched together areas. But I always GS in between – same as the walls. I’ve been working on my rim joists/walls for about a month and a half (large basement, little time). If I had to do it over again, I would definitely re-consider spray foam for the rim joist. The walls are not an issue but the rim joist is extremely difficult. There are many areas that are ‘do the best you can’ but I’m not sure this is really a case where ‘do the best you can’ is a very good option.
Steve – Some rim joists are definitely hard to work on. Newer homes are easier to deal with compared to older homes. I hope your efforts pay off. Good luck.
Todd,
Do you recommend applying waterproof paint to the concrete walls before installing the foam?
Thanks in advance,
Victoria
Victoria – People ask this all the time. It certainly won’t hurt anything but I’m skeptical about how much it can actually help. Trying to seal out water from the inside is a very low odds attempt. It may help keep some water vapor at bay but it won’t stop water that leaks through from a high water table.
Thanks for all the wonderful information on this site. We are building a new house in NW Ohio, I was wondering about your thoughts on spray foaming the interior of the basement walls (closed cell) in place of the foam board, and how thick would you go. I know it would be pricier but would it be worth it? Thanks
Steve – Spray foam is certainly the best approach when it comes to being the best R value, and eliminating air leakage and locking out foundation moisture. It really comes down to a cost issue, most spray foam jobs will cost many times more than a DIY foam board job.
I have also heard that the foam board puts off an extremely toxic gas if it ever catches fire and needs to be painted with a special paint) if it isnt covered by drywall, is this true?
Steve – All foams are toxic when ignited. All foam, including spray foam should be covered with an appropriate fire rated wall assembly according to local codes. When no code specific requirement is found most foam board manufacturers suggest at least a 15 minute rating (1/2″ drywall).
If using spray foam how far away from the concrete should I build the wall, and should green board be used or regular drywall?
Steve – I would leave an inch space or so…that way foam gets behind the studs. Regular drywall is fine for this application unless it’s a bathroom
If doing a drop celing in a basement would you use anything in the area between the floor joists and the drop celing for insulating or sound proofing? Kids will be using basement for tv and playroom.
Tim – Fiberglass insulation will help a bit. I’d use unfaced.
You would use fiberglass over roxul safe and sound or something similar?
Tim – It really depends on the situation. Roxul Safe’n'Sound is a fire resistive insulation. Do you have a fire rating issue with your design? If you’re looking to just do sound then regular fiberglass is fine. You will need to be careful about using IC rated light fixtures.
Have you ever used paperless drywall for a basement? A basement seems like a good application for it. I’ve read that it is difficult to work with as it requires a skim coat in order to look “right”.
Steve – I have not used it. It certainly is an appropriate use for the product.
We are building a 2800sq ft one story brick house, the basement will be approximately 2000sq ft with 1800 finished. My question is will I need to insulate the unfinished rooms and crawl space walls the same as the finished rooms way to be energy efficient?
Also if using spray foam what R value should I be trying to get in the finished area?
Jim – First off it’s important to know that most states now have some type of energy code that’s tied into the building code. The energy code typically establishes minimum R values.
The unfinished portions don’t necessarily need to be insulated but you will need to insulate the floor above that area.
Hi Todd -
Love the video! Because of your advice, we’ll be finishing our basement the right way. I will be using 1 1/2″ foam against the cinder block foundation, sealed & taped. We’ll then 2×4 frame out the walls, where I plan to add another 1 – 1/2″ foam board in the 16″ cavities.
My question comes here, in regards to the finishing of our walls. We have a log home, and will be using 1×6 cedar siding to finish the basement walls to remain consistent with the rest of the house…so, no drywall.
Will this be okay from a toxicity point of view?
Thanks!
Casey – Thanks for visiting the site. I take it you’re asking whether or not the foam will release some sort of “gas” that might not be healthy correct? I’m not familiar with any reports to that affect. I do know that XPS foam board is used in millions of homes in many different ways from foundation insulation to attic insulation. If you’re overly concerned about it you might want to install a layer of poly over the final foam before you finish the walls.
Todd, Would it be beneficial to paint the concrete walls in my basement with a Drylock paint or some variation before applying the foam boards? Thanks for the info.
JP – Let’s put it this way. It certainly can’t hurt with water vapor. However, it’s not going to stop water from coming in if the ground water penetrates the concrete. It’s not necessary but it is a belt and suspender approach.
Todd,
Two more questions. I’m trying to minimize the amount of space taken up by the framing. Would you advocate DOW styrofoam wallmate xps sloted edge with furring strips? Also what would you do with an interior block wall that divides the two basement rooms? I was just going to lay 2×4 flat and no insulation.
Thanks,
John
John – The wallmate system will work, just be sure to seal the seams really well. Obviously it’s not as good at the other approach but should do an ok job. The interior wall is fine as you describe. Good luck.
[...] the walls, you may want to consider insulating the floor in the long wrong. Todd’s article on basement insulation gives some coverage on this [...]
Hello,
Great site, with lots of information!
I am in the planning stages of finishing my basement. My house was built in 2010. I live in central Ohio. I have a Tremco barrier solution on the exterior of my block wall foundation
http://www.tremcobarriersolutions.com/products/default.asp?id=1
http://www.tremcobarriersolutions.com/fileshare/specs/TBS-0518%20TNDH8%20Spec.pdf
The builder claims the insulation board on the exterior block wall is giving me an R5 (below grade only). Does having the exterior insulation change my approach to insulating the interior basement walls? I was planning on using either 1.5” or 2” XPS (Owens Corning Foamular) on the entire basement wall and probably on the basement floor too. Then studding out walls in front of the XPS.
Thoughts?
Thanks!
Troy – Tremco is a great company with great products.
I wouldn’t change anything about your approach. You’ll have a really great finished basement with your approach. Good luck.
Thanks for the reply, Todd!
Do you think I can get away with 1.5″ XPS? I was leaning towards that since it is around $12 cheaper per sheet and because I already have R5 on the exterior. I was not planning on using fiberglass batts in the stud cavity.
Thanks!
Troy – I think that will be fine. I will say you should check to see if you have any local energy code requirements though.
Hi Todd,
We have just recently started to finish some rooms in our basement. The outside walls were already framed directly on top of the concrete. A friend of mine in construction told me to just use plastic sheeting as a vapor barrier. We were able to slip the plastic behind the framing so that it is in direct contact with the concrete. We were going to then insulate with batting and then drywall. But from research I’ve done, I don’t know if this is a good idea. Won’t any moisture just run down the plastic and into the floor and rot the 2×4 on the bottom of the frame? We’ve been in the house over a year and haven’t seen any condensation, but I’m not sure the best way to go. We really don’t want to have to take the framing out. Any suggestions?
Thanks!
Jessica – I can tell you that putting plastic sheeting in that fashion will almost certainly result in a mold problem. There are thousands and thousands of examples out there using that detail which results in a horrible mess.
Here’s why: The plastic will stop moisture in the foundation from getting to the fiberglass. However, it won’t stop any damp air that is inside the framing from coming in contact with the “cold” plastic (the plastic will be around 50 degrees, same as the concrete) which will then condensate into a liquid.
If it were my home, I’d simply cut any fasteners between the slab and bottom plate, fasteners between the top plate and framing above, slide the wall out, install foam board (XPS) and do this right. It will take some effort but you’ll be sorry if you don’t do this right.
Todd,
I have a 3′high concrete kneewall in my basement. There are currently 1×3 furring strips every 16″ and ramset into the concrete wall. I want to put 2″ foam against the concrete but that means I would have to remove those furring strips which looks like alot of work. Instead, Can I glue the foam on top of the furring strips and sheet rock rock over that? There would be about 3/4″ gap from concrete wall to foam, but wouldn’t that air gap be good? (air is an insulator), Should I fill the gap with “Great Stuff” or 3/4″ piece of foam? Thanks.
-Ethan
Ethan – You can do that but it’s likely that years down the road (possibly a long time) the furring will decay. If you’re ok with that then go for it. I’d probably do that in my own home if there were too many to remove.
Thanks for your quick response Todd. Do you think attempting to fill the gap between the concrete and foam panel with “Great Stuff” is a stupid idea?
Stupid no…realistic no……I wouldn’t bother!
I am redoing my basement. It was previously done about 25 yrs ago. On the walls they nailed furring strips to the concrete block wall and put expanded polystyrene insulation between the strips then drywall over it. I have torn all that out and filled in the nail holes with hydraulic cement. I am also applying several coats of a high strength elastomeric liquid rubber to the walls and floor as a water and vapor barrier. I am going to glue XPS insulation on the walls as you suggest and tape the seams. What thickness should I use of the XPS 1″ or 1.5″? The previous polystyrene was only 3/4″. Now I am wondering how I can attach the drywall. I can not nail into the floor or walls with them sealed. I have thought about gluing the drywall to the XPS or attaching furring strips and screwing drywall to the furring strips Any suggestions? I do have one other question. I have seen a product in Lowes and other home improvement stores. Its called Reflectix foil insulation. What applications would you use such a product? thanks.
David – Honestly I think you’ll need to experiment. Not sure what is ging to adhere to that rubber. Not sure adhesives alone will do the trick.
I am going to insulate my rim joists with foam board. I previously had fiberglass stuffed in there. Do I need to cover the foam board with drywall? Or can I just stuff the fiberglass back in there?
thanks.
It really depends on your local building code requirements. There are some areas that require a 15 minute thermal barrier over it (i.e. 1/2″ drywall). I’d check with your local building inspector for clarification.
Forgot one thing, how do I insulate the rim joists around an electrial cable coming in and also around heating ducts. thanks
You do the best you can! :) The idea is to insulate as much as you can, use spray foam in places you can reach and even fiberglass as a last resort.
My local home improvement stores don’t carry the 2″foil faced polyiso board, but I did find some 1″ foil faced sheathing, so I am just going to double it. I do have a couple more quick questions:
1. In your video, I saw the ceiling of the basement insulated. I have heard that this is a waste of money, whats your thoughts.
2. I have room in my basement that is right below a bedroom. How can I deaden the sound from this room? Is there special insulation or materials?
thanks again.
That ceiling is insulated because the floor above has radiant heat. So it has to be insulated in order to work properly.
The sound issue depends in part on the type of ceiling you’re going to have. If you tell me what you’re going to use for a ceiling I can better help you figure out a sound solution.
It currently has a drop ceiling in it. The ceiling also has phone incoming lines, electrical incoming line and also water lines.
Accoustic sound insulation is your best bet. If you were using a hard ceiling like drywall, you could use channel hat strapping to further isolate the noise.
We are planning to insulate our basement with foam board. Two walls are not a problem as they are floor to ceiling poured concrete but the other two are stumping us as they are part poured concrete from floor halfway up the wall, then the wall steps back (pony wall?) and has already been insulated with fibreglass insulation and then covered with a vapour barrier by the builder.
Ive read conflicting articles regarding drywalling over this some saying the vapour barrier should be taken down and others saying go over it.
We are planning on taking the studs from floor to ceiling giving a flush wall as opposed to keeping this pony wall and Im not sure how to go about filling in the void this would leave.
Also Im in Newfoundland where the strong, bitter winds tear through the property so although we were planning on using 1″ foam board I’m guessing that this isn’t anywhere near enough. On another point we are also planning to use dri cor on the floor and some say we should put these down first before we insulate the walls, others say to do this afterwards, which is right?
You have several issues here that are pretty straight forward. Before answering them I would suggest you read a couple of other articles here on the site.
http://www.homeconstructionimprovement.com/how-to-insulate-basement-walls/
http://www.homeconstructionimprovement.com/vapor-barriers-for-basement-insulation/
So for your situation there are a few things to consider.
You can either leave the existing insulation and vapor barrier on the framed wall. If you do this DO NOT add additional insulation above the concrete in your new wall.
You can remove the vapor barrier and add additional insulation above the concrete, then add a vapor barrier.
For the lower portion against the concrete I recommend a minimum of 1-1/2″ of XPS foam between the concrete and framing. 2 Inches would be much better.
Then add the framing and additional insulation in the stud bays. You can then add your vapor barrier in front of that.
It’s certainly ok to install the Dri-Core first then install the insulation and wall framing on top of it.
Best of luck. If you find our site useful please consider ‘LIKE’ing our Facebook page: http://www.facebook.com/pages/Home-Construction-Improvement/248544769916
I am insulating the rim joists with foil faced polyiso foamboard and foamed them in with great stuff. I then have to put drywall over that. What is the best way of attaching the drywall? Does the great stuff foam have to be covered with drywall also?
The easiest way would be using adhesive. Once you have the pieces of drywall up you’ll likely be required to fire tape them and use joint compound around loose edges.
I have a few hopefully quick questions:
1. I have put up XPS foamboard on my walls and sealed the seams with tyvek tape. Do I seal where the foamboard meets the concrete floor? With great stuff foam or just tyvek tape?
2. My Father in law has talked me into putting up a stud wall after the XPS foamboard because of easy install of drywall and electrial outlets. What insulation should I use? fiberglass, faced or unfaced?
3. If I insulate between the floor joists on the ceiling should I use faced or unfaced insulation? If faced should the paper be towards the first floor or towards the basement?
4. Lastly, the rim joists, I have to areas where a heating duct runs along side and its very diffcult to put foamboard in there. Can I put fiberglass in there and how far away from the heating duct does it have to be? Also do you put anything on top of the sill plate for insulation?
Thanks for all your advice, so far have found a lot of cold air leaks.
1. There’s no correct answer for this as it really depends on your basement. Does your basement have any history of water trouble? If so you probably shouldn’t seal it, so there’s a way for water to get out. If no water problems then we typically seal it with foam.
2. This depends on several things; what R value does your local building code require? What thickness foam have you used? If you’ve used at least 1-1/2″ foam then you can use either. If you used less than that then it’s a more difficult answer.
3. I prefer unfaced in that situation with wire supports to hold it in place.
4. In those situations I typically use Roxul insulation, it’s fire resistant and better at dealing with moisture problems.
Good luck!
I used 1.5 inch thickness of the foam. From what I could find out the basement wall insulation should be a min.R-11. So what would be good for my walls? thanks.
So right now you have between R6 and R7. If your basement is fairly dry then I would just use some Kraft faced fiberglass to give you an additional R11 in a 2×4 wall.
Do you have a preference between fiberglass rolls or batts? Money wise is one cheaper over the other.
There’s no difference. Depending on the height of the wall sometimes batts are the right length and don’t require cutting.
Todd,
I stumbled on your site and would like to thank you for the information. I have a couple of questions.
I am attempting to finish our basement.
Some facts:
We have sump pump installed, 6″ tile at the perimiter base of the interior footer. Runs regularly, source of water is a nearby spring running in from under the floor. When the floor was poured a weep at the base of wall was installed using furring strips. I’m guessing it was to handle any seepage through the block at the base and direct to the crock or maybe to equalize. Although I have never seen water along base of wall. I’m planning to use 2″ BBoard, frame & insulate per your earlier posts.
Question-
1.Should I fill in weep with hydraulic cement as it may actually be contributing to moisture problem or just run BBoard to top of floor sealing it off? and flooring to it.
2. What are your thoughts of the “Rigid OSB Panels” as subloor.
Thanks
TJ
TJ – My Pleasure.
1. Do not fill the weep, it needs to be there. If water does come through it the idea is that it will stay behind the blue board and find it’s way to your drain.
2. Dri-Core and similar are very good products for basement floors.
Todd,
Again, thank you for your valuable input !
Todd great website, lot of helpful info. Here is my story:-
I have a split level home on Long island, NY . I have a partial basement about 300sf with 7ft celings. I am trying to finish that and make it a play room. When I first bought the house 7yrs ago I used to get water in the basement during heavy rains but once I moved all the down spots from the gutter away from the house I haven’t had any water issues except it does get little humid I the basement. I have poured concrete walls and floor. House wase built in 1958. I do see some arears on the wall where concrete is chipped away and it’s white. I hope I am explaining it right. Here is my plan and few questions:-
I will use 2 inch xps board glued to concrete, tape all the joints then 2×4 filling with roxul comfort batt then sheetrock
For ceiling I will use roxul safe and sound and then sheetrock
For floor I will use delta-fl and then ½ inch osb all the walls will be built on top of the osb.
Here are my questions.
1. do you see any issues with my plan?
2. do I need to clean the concerte and apply anything ?
3. Should I use dryloc or any other similar product?
4. for the walls should I take xps all way down to the floor and then do delta-fl butt up against it or do delta-fl butt against the wall and end xps on top of it?
5. do I need to use vapor barrier between 2×4 wall filled with roxul and sheet rock?
I am just trying to make it as comfortable as possible. One of my kids does have some environmental allergies. So I want to make sure its done right. I am assuming I have to run dehumidifier during peak summer months. Any other advice or thoughts?
Thanks for the nice compliment.
1. Only thing that I would change is the 1/2″ OSB on the Delta-FL. I would use at a VERY minimum 5/8″ thick. Also, I would use a product that has exterior grade (A-C, B-C or CDX) as they have adhesives that are resistant to damp conditions.
2. Not really. I just suggest you fix any cracks or spalls before you begin.
3. I’m not convinced those products really work that great. They will help stop some vapor movement so they certainly won’t hurt. I’m on the fence as to how well they work.
4. I would do XPS to floor, delta-fl up to that.
5. no.
Best of luck with your project. Don’t hesitate to ask more questions if you need further assistance.
If you want to help us out, we’d love to have you LIKE our facebook page, http://www.facebook.com/homeconstructionimprovement
thank you for your advice. just supported you via facebook. i am sure i will have more questions once project starts. i am in the planning phase.
Any time…..I enjoy helping out.
I am using the 1″ blue foam in my basement. It is not a living space , just storage work area. I am thinking of using corrogated pvc, just like the signs are made of.I am going to glue it to foam. Do you think this will be ok?
Are you suggesting that you’re going to use 1″ foam board then some sort of PVC board as the finished surface? If that’s the case I’d say a few things.
1. 1″ foam board isn’t sufficient to create an effective vapor barrier.
2. A PVC finished wall surface likely does NOT meet building code requirements for flame spread ratings and is likely not a legal surface, living space or not.
I have a 28 x 60 basement, about a 1/4 of the end sticks out of a hill, I’m costing out the difference between going with 2-1/2″ xps at r-12.5,- with a framed wall with no additional insulation, or 2″ xps @ r-10, with a framed wall with fiberglass batts.
If I use the batts in the wall with the 2′ xps, do you use faced batts or just plain? –thanks you for your time, I’m sure we all appreciate it—Kevin
You can use either one. With 2″ of foam I prefer to use unfaced.
Hi Todd — fantastic site. I’ve learned so much in the last day of poring over your articles I can’t believe it.
Here’s my question — I have been looking at some of the DYI two-tank foam kits. My original plan was to use 2″ blue board glued to the wall and then use the spray foam in the rim joist area. I then thought — I wonder if I could use that to actually glue the blue panels on? e.g., spray a stripe down the wall and plop the panel in it. Great stuff seems very expensive — I tested it and got about two panels glued up before the can was empty. And that was just going around the edge of the panel, and then making an “S” curve down the center. I haven’t tried the caulk-type stuff yet. I’ve not seen any articles about simply spray foaming the entire foundation wall — it always seems to be sprayed on after the studs are up. Is spray foaming the wall and putting the studs up afterwards even possible? Any thoughts? Thanks.
Mark – Thanks for the nice compliment. I sure hope you bookmark the site and LIKE us on Facebook so you can keep up to date with all of my great articles.
The kits would certainly work for attaching the foam board. Frankly it takes VERY little foam to get it to stay on the wall. If you get the boards tight you don’t need much to seal them and I always use tape afterward.
Spraying an entire wall would be insane with DIY kits in my opinion. Also, spraying after framing gives them a good surface to adhere to and use as a depth gauge. I’d stick with the foam board and spray foam in the rim joist area.
Good luck!!
Todd:
Great site. I read thru many of the questions and I have a couple myself. My basement has a small history of water. Maybe once a year if a gutter overflows I will get water trickle on the floor. I can see wet spots appear on the walls which has caused the masonry coating on the block walls to flake off in places. With that said can iso foam panels still be attached without causing a trapped moisture/mold problem? I don’t want to finish with frame/drywall I was thinking more of a FRP panel for final surface. Basement is used for storage/workshop only. I think this will trap any moisture behind the insulation against the block walls and will drain to floor. Does this idea sound ok?
Thanks
In that use it will be ok. I wouldn’t recommend a traditional finished basement but your situation sounds fine.
Todd:
What happens to a basement that has iso foam on the walls that develops a leak and ends up wet behind the foam? Does mold form? Will the foam degrade? Thanks
Steve iso foam is a closed cell foam (at least the ones I’ve worked with) so water won’t be absorbed and won’t bother the foam. No worries.
What about mold? Can it still form on the damp wall and spread? Have you ever removed foam and seen mold? Thanks
Mold needs a food source to grow. Molds need food and nutrients and moisture to grow. Foam is not considered a food source for mold unlike wood, paper and other traditional building materials.
If i use two layers of 1″ foam and stager the seams would I still need to tape the seams? If so would both layers need taped or just the outside layer? Thanks
I would tape both layers.
Im just curious as to why you suggest taping both layers. Thanks for all your advice.
1″ foam doesn’t stop water vapor. See the following article:
http://www.homeconstructionimprovement.com/vapor-barriers-for-basement-insulation/
So if you don’t tape the joints, then you’re going to allow moisture to get through them and possible through the last 1″ layer. I just wouldn’t risk it for the little money and time to tape the joints.
Hello,
I’m not sure if I have a problem here…..
We bought our house a year ago and are re-finishing the basement, which was finished in the 70′s with paneling and shingles nailed to the wood frame.
We have one wall that is exposed brick, which we have painted and are leaving. Most of the rest of the walls are interior walls, enclosing the utility room and laundry room. There are only two small walls, approximately 8′ wide, that are exterior, concrete walls.
It appears that for the two small concrete walls that there was brick, then some kind of wire mesh, then thick concrete in front of that. When we took down the old shingles and paneling, there was no mold or moisture behind it, or on the wood frame which is very close to the concrete wall (actually touching in a couple little spots). We had a mold company come and test for mold and moisture, and they tested the wood for moisture, and it was dry.
What we did was put a fresh coat of dry lock paint and put thin foam insulation between the wood beams. Then, we put mold/mildew resistant sheet rock up over it.
Now I am worried that we should have somehow moved the wood frame out and put the insulation behind it before the sheetrock. Do you think we have anything to worry about? I was hopeful because the wood frame has been there for many years without collecting mold, and also, there is that layer of concrete in front of the bricks.
What is your advice? Should we take down the sheetrock there before we go any further and do the insulation as you have described above? Or should we be ok?
Thanks so much for your advice
Your situation is not that uncommon. Back in the 70′s and even 80′s lots of basements were finished without insulation. Fuel was cheap and people just cured cold drafty areas by applying more heat.
Fast forward to today and many states have energy codes that require a minimum amount of insulation and proper vapor barriers.
With the old detail the wood paneling could easily breath and let moisture escape. Now, if you install a tight wall finish like drywall the moisture has no place to go. So you MUST install a proper vapor barrier and proper insulation otherwise you have a very high risk of mold and mildew.
If it were my home I would not leave it as you have it currently.
Todd,
Thank you for your reply, it is very helpful. We are installing a drop ceiling, would that provide additional room to let the air breathe and let moisture escape? Additionally, there are gaps in the basement which prevent the sheetrock from completely sealing off the walls. For example, if you go into the far corner of the boiler room of the basement, you can actually see behind the sheetrock and see some of the wood frame. Would you still recommend taking down the sheetrock and bringing the frame further out, if it were your house?
Again, thank you so much for your help and taking the time from your vacation to personally respond to our questions. Our apologies for sending the message twice, we weren’t aware that the posts were removed prior to your response.
Kate – Part of the answer really depends on where you live, what the code requires and how much effort you want to put into it. I’ve seen far too many horrible mold problems that I don’t ever want to risk it.
No worries…it’s my pleasure to help. The comments don’t actually go live until I review them and approve them. Unfortunately I have to do that to stop spam and profanities.
I hope you’ll consider signing up for my FREE weekly newsletter or our Facebook page.
Good luck.
Hi Todd,
My wife posted about this earlier today but it appears as if her post has disappeared, so I am re-posting with the same general idea she wrote about.
We are currently in the process of renovating our basement. There was previously paneling and wood shingles attached to a wood frame. We tore the paneling and shingles down but left the frame up and had a mold company come in to examine the basement. They found no evidence of mold and tested the wood frame for moisture as well.
Without getting into too much detail, only two of the walls we are re-doing have framework that lies very close to the basement foundation, and in a few instances one of the studs will touch the wall behind it. These walls are approximately 8 feet wide. From what we could decipher, it appears that the foundation consists of brick, then some sort of wire mesh (?), then concrete over that. The concrete is what the wood framework lies against. The mold company painted over the concrete with some sort of drylock/moisture resistant paint. We put thin board insulation in between the studs and then put mold-resistant sheetrock on top of this.
Our concern is that since some of the studs touch the wall behind them, there is the possibility of mold collecting on them. There is no water seepage along either of the two walls, but if we try to put an air conditioner or heater down there we are afraid that might create a greater opportunity for moisture to form and collect. I talked to the mold company we worked with and they said that the overall square footage of the wood that lies along those two walls is minimal and not enough for mold to germinate and become a serious problem. They also said with the lack of water seepage along these walls and the dry lock, a good dehumidifier or two would be substantial in eliminating any excess moisture/condensation that might come as a result of putting in an air conditioner or heater.
Do you think that we will be okay or do you think before we go ahead we should take the sheetrock that we put up down from these two walls and do what you suggested above in your advice?
Thanks!
Rob – I responded to hear earlier post. All comments have to be moderated by myself before they show up. I’m on vacation this week so the responses are slow. Check out the response I left for her comment. Thanks
Todd,
First of all I wanted to say great site.
I live in Syracuse, NY so the winters get quite cold. We had a house built last year and the foundation is an 8ft poured cement wall that is completely above grade, we are near the water so we wanted the house up high just in case there is flooding. I was planning on using some kind of foam board on the concrete then framing with 2X4 and using R-13 kraft-faced insulation.
How would you handle this project?
1. What kind of foam board would you use and how thick?
2. should I use Drylock on the cement first?
3. Should I use kraft-faced r-13?
Thanks for any advice,
Ken
Thanks for the kind words.
First off I’d suggest you read a couple other articles I have which will also help you understand the project:
http://www.homeconstructionimprovement.com/how-to-insulate-basement-walls/
http://www.homeconstructionimprovement.com/vapor-barriers-for-basement-insulation/
So after reading those you’ll see that I recommend at least 1-1/2″ of closed cell foam board (XPS – you can use the blue or pink brands). Drylock isn’t necessary unless you have a foundation that seems to be very damp. If your basement is fairly dry I’d use unfaced insulation.
Good luck and I hope you consider signing up for my FREE Newsletter that’s full of great home improvement tips and advice.
Todd,
Since this wall is above grade and completely dry I was thinking about using 1″ of Polyiso, then framing a 2X4 wall over it and fill the cavity with r-13 kraft-faced insulation. I don’t think moisture from the outside will be an issue. Would this be a good solution? Space is an issue that’s why I was going to use the 1″ board. Do you think the Polyiso is a good choice for this or am I better off using the XPS?
Thanks,
Ken
If space is an issue then I’d recommend you use the 1-1/2″ min and use 2×3′s to frame the wall.
Hi Todd,
We are located in NJ and we have a cinderblock basement with an interior french drain that has a 1 inch gap around the perimeter walls. The lowest row of blocks have holes drilled in to release the water from within the cenderblocks and into the drain. The water is directed into a sump pit and then pumped outside. We don’t have a big water problem. We want to finish the basement and want to know if blue board insulation can be used with this french drain system. If so, what would be the best way to install and seal? How would we seal at the floor level considering the 1 inch gap and not disturbing the functionality of the system?
Regards,
Donna
The weep holes and 1″ drain gap will be fine even with the Blue Board Installed. I would install the foam board and leave a very small gap at the bottom (maybe 1/4″, use some shims). This will all any water to get into the drain. By installing 1-1/2″ or 2″ of foam board the framing will be in front of the hole and not over it. Good luck.
Todd,
By leaving a 1/4″ gap at the bottom, would that interfere with the blue board working as a vapor barrier?
yes and no. If you want to help that situation you could apply sealant to the back of the bottom plate of the wall framing when you push the wall up against the blue board, that would seal it. I wouldn’t worry about it all that much.
Thanks Todd! We appreciate the advise!
My pleasure. Best of luck. I hope you’ll consider signing up for my FREE Weekly Newsletter for all kinds of Home Improvement advice.
Most of your information is for inside basement walls. We have about 6 feet of exposed rock foundation on the north side of our house. Originally this was the billiard room to a house built in the late 1880′s. Now this north facing room is a Kitchen with a cold concrete floor. We are getting ready to put a deck covering that north rock foundation wall. Is there any good way of insulating that rock foundation wall to the outside? And would insulating it help the kitchen floor to be warmer? Thanks for sharing your knowledge,
That’s a tough question and one that I’m not sure I have a good answer for. I might be included to frame a pressure treated wall in front of it and then spray foam tthat with closed cell foam. Then you’d have to side it.
It might help the floor a bit but not likely all that much.
Thank you for your reply. We don’t want to put our money where it doesn’t return much results, but we didn’t have a clue, except the Kitchen is the coldest room in the house and know we’ve got to do something.
Thanks again. You do a good work for the DIYer.
My pleasure. You might want to consider insulating the kitchen floor if you have the headroom.
Thanks to your site and your prior replies & research on building science I had decided to go with a 2″ foam with no fiberglass. I have 1″ foam on exterior with a rubberwall on a 9″ poured wall. I went to get my permit today and learned that my city does not allow any foam on the interior because of “carcinogencs & flammability issues” – even spray foam requires you submit MSDS sheets and have it behind a poly vapor barrier. So it appears my only option is a standard kraft faced R-13 fiberglass. Any advice on how to make that work… now thinking frame the wall 1″ off the poured wall and then R-13 with vapor barrier. I’m in KY so not much of a cold issue. Thanks for any other advice”
I’m really shocked and think that your local building code is flawed. This shouldn’t be an issue if the foam is covered with an approved heat barrier such as drywall. Frankly foam board is far less likely to offgas than spray foam so why not be able to use the poly layer over the foam board?
Also…I’d check with your State Building Code officials to see if the code is being interpreted correctly.
I just can’t recommend the fiberglass only approach.
I think I posted this somewhere else… but I can’t seem to find my post…
Hi Todd,
I have a quick question about the preparation of my poured concrete walls before I put up the blue/pink foam. My wall have what seems like verticle seems running down the wall every 4-6 feet, as well as little circles every 2 or 3 ft, I assume that this was created during the pouring of the concrete. Both are raised at most 1/4 of an inch from the rest of the concrete wall… my question is:
1 – Should I chisel away the raised seems and circles to ensure the rigid foam goes directly against the concrete?
2 – Is it prefered to use 8ft by 2 ft foam over 8ft by 4 ft?
3 – would you recommend screwing the adhesive to the concrete as well as gluing it?
Thanks for your help!
Those lines are just the seams in the concrete forms and the circles are where the form ties are. Chipping it away is one option or you can leave as is if you have enough room with the finished wall layout.
I like 4×8 sheets because there are less joints to seal.
No need to screw it to the wall.
Good luck.
Hi Todd-
Great site and information!
I’m starting up a basement finishing project and I’m planning to use 2″ XPS on the walls with 2×4 studded walls in front of them (w/ fiberglass batting in between). My question comes on what I see as a 10′ horizontal fireblocking code requirement – do you have any recommendations on this? My concern is that by the code (if I interpret correctly) I’d have to have a fireblocking material contact to the concrete wall every 10′ horizontally – my concern here is disrupting the vapor barrier created by the seal XPS.
One though I had was to make a 1″-2″ gap in the XPS every 10′ and filling this gap with fireblock foam…then when I stud the wall I could extend my floor to ceiling fireblock up to this foam. Any thoughts?
Thanks for all the help!
Not sure what code you’re using but I’m not understanding your interpretation. Fire blocking typically requires that you can’t have an open chase from one level to the next or more than 10′ vertical (again this varies by code). In other words, if you’ve got a space behind your framing it cannot run up to the framing on the next floor or more than 10′.
Most modern homes are framed with the deck extending out to the rim joist, this in essence creates a fire block from the basement to 1st floor. In some situation the code is interpreted such that the basement framing must extend up to the bottom of the 1st floor deck. When you do this, and extend foam up to the bottom of that deck, you’ve typically got to protect that foam with a 20 minute thermal barrier (1/2″ drywall, certain plywoods, etc.)
Make sense?
Hi Todd,
Maybe I’m mis-interpreting the code here (R602.8), but I see a requirement for both vertical and horizontal fireblocking. My concern is with the 10′ horizontal / side to side requirement and how to effectively block this off without losing the benefits of the xps vapor barrier.
“In concealed spaces in stud wall cavities, partitions, and furred spaces,fireblocking needs to be installed at the ceiling and floor level and at 10’intervals both horizontally and vertically to minimize draft flow and to
suppress the mitigation of flame”
Maybe I’m reading into this too much but it seems I need to make a ‘break’ every 10ft along the length of the wall.
Thanks again,
Tony
You’re reading it correctly. However, your interpretation is off a bit based on my experience with this topic.
If you run the XPS from slab up to top of foundation wall, and then studs running up to bottom of floor/joists above, the studs are the breaks horizontally. The foam isn’t considered a “void” as it’s a filled space. Even fiberglass insulation can be used as a fire blocking. So if you get your foam in, then you can fill the voids with fiberglass. make sense?
OK – great, makes sense….and a lot easier than trying to break in to the XPS every 10′. I will be using fiberglass batting in between the studs so I’ll make sure to fill in all the voids as I expect some some air gaps between the stud wall and the XPS due to the foundation not being perfectly level.
Thanks again for the input & advice, great site!!!
Tony
Hi Todd,
I went to our local building inspector to apply for a permit to finish my basement and took the opportunity to ask a few questions. I mentioned that I had two inch foam on the exterior of my foundation and would that negate the requirement to have insulation on the interior as well (the house is about 6 yrs old). He said that it would not be required.
I then asked about using vapor barriers and what are the current requirements. He said the state of Wisconsin does not permit vapor barriers at all in the basements. I then mentioned my intent to use foam boards on the interior between the wall and the frame. He said that would be fine as long as I don’t tape the seams, creating a vapor barrier.
Can you give me your thoughts on the above? Should I insulate given the fact that i have exterior foam? What about the vapor barrier, should i put in the foam on the interior but not tape the seams?
Thanks,
Dale
Sounds like the inspector doesn’t really understand the issues nor the code. In one breath he tells you no vapor barrier and in another he says seal the seams…..
I’ll be the first to admit I have no idea what code the State of Wisconsin is using. However, if you want a dry, warm, comfortable basement I would HIGHLY recommend you insulate the interior walls with closed cell foam board. You’d be crazy not to tape the seams!
Thanks Todd,
What about the fact there is 2″ on the exterior of the foundation? Do I still need to insulate the interior?
And to be clear he said to not to tape the seams?
It seems logical to follow your suggestions. What venue would I have if I install all of the fan and tape it and the inspectoR wants it removed? Can I appeal to anyone?
Thanks,
Dale
In my opinion you do need to still insulate on the inside. For two reasons.
1. Your exterior insulation probably isn’t continuous up to the house insulation.
2. The exterior insulation will NOT prevent water vapor (that exists for the life of concrete) that is in the foundation wall from drying to the inside and causing mold/mildew problems with the basement framing/finish.
The authority on all this is buildingscience.com
You need to find a way to work through this with the inspector. It is my STRONG belief that he/she is way off base here.
I have a question about fireblocking… when using the XPS foam are you required to have a gap every 10′ horizontal filled with 3/4″ plywood or 2x lumber tight to the foundation wall to satisfy the fireblocking requiremnet or is simply placing the wall tight to the foam ok?
I read that portion of the code differently. If you look close at the code you’re allowed to use insulation as fire blocking including fiberglass. Fire blocking helps stop drafting fire. So I maintain that if there’s no air space there’s no issue with fire blocking.
Todd,
I have a question about framing/finishing my basement. I have a stone and mortor basement foundation wall, which does allow some moisture to pass through. As such I do see efflorenscence on parts of the wall. I run a demumidifier all year.
My question realtes as to what type/s of insulation I should use as I frame out the walls. My thought was to frame the walls about 1 foot away from the foundation wall in the following order;
From the wall in; Rigid foam insulation, plastic sheeting, both attached to the back of the framing. Then insulate further with fiberglass batt insulation, followed by another layer of platic sheeting and then drywall.
I will be using the wood floor panels with the plastic on the bottom to allow the floor to breath as well.
Will this work do you think or should I attach the rigid foam directly against the wall first…its very uneven so not quite sure how I would do that successfully.I also dont want to trap moisture that comes through the walls against the rigid foam, all be it that the foam does breath to some extent. My thinking is that the gap between the stone wall the rigid foam attached to the studs will allow it to breath while also keeping from condensation forming on the walls or rigid foam.
Any help is appreciated. Thank you.
Gary
Gary – Your close. I’d change a couple things.
- Foam, taped and sealed at all joints. The tape can be on the back side if you want to install all this on the frame first.
- No plastic.
- Framing.
- No plastic.
- Consider using a product like Roxul which is completely mold proof.
Good luck.
Tod,
I am insulating my basement with XPS 2″. Against the sill I have placed the foam board and then used great stuff. There is a grounding wire against the foam as it was stapled against the sill.
Is this a fire hazard? Can I leave this or do I need to pull this off and do something else?
Joe
Leave it where it is. It’s a grounding wire, so long as it’s not cut it will be fine.
Hi Todd,
I am starting to work on my basement, I will be insulating with the foam board just as you have described,I have several questions.
You said I do not need to put 6 mil plastic on the studs before sheet rock as long as the sheet rock and paint are installed in a timely manner. What is that time frame?
The foam board requires a fire block,is the R-13 insulation a fire block or do I have to use 5/8″ sheet rock as a fire block?
Do I need to put 2″ x 4″ fire blocks in the studded walls?
Last question, I have radiators on the main floor of my house,so I have a 1″ copper pipe that runs around the perimeter of the basement, should this pipe be inside the wall between the foam board and studs, or should I move it to the inside of the finished side and hide it in a bulk head?
Thank you for taking your time in helping all of us.
Mike
Ideally you’ll at least get one coat of tape/mud on soon after you hang the drywall.
Most codes require a 20 min thermal barrier which is 1/2″ drywall. Fiberglass can be used for draft stopping but not a thermal barrier. Some products like 1/2″ OSB do meet the flame spread criteria and thus the thermal barrier requirement.
Draft stopping is dependent on the code you’re using. Typically blocking is installed to stop drafts from one story to another. If you have a sub-floor in place then they typically would not be required.
The location of the pipes isn’t super critical. You don’t want them in a place that might freeze. If they are inside within insulation that’s fine.
Good luck.