DIY Basement Insulation Video
Insulating Basement Walls with XPS Foam Board Insulation
I’ve written quite a few articles about basement insulation and showing folks how to use foam board products instead of fiberglass. I recently made a quick video highlighting the approach on using XPS Foam Board Insulation to insulate basement walls.
The video talks about insulating the rim joist with foil faced polyiso insulation, how to deal with concrete knee walls and lastly how to install 2″ rigid foam board insulation over a concrete wall.
Awesome job Todd!
Question about using foamboard to insulate basement wall.
At the end of the video,you mentioned not to use Poly against a concrete basement wall. What is Poly?
Also, it didn’t seem that you glued the foamboard against the concrete. Isn’t it better to glue the foamboard so that warm air doesn’t convect behind the foamboard and create moisture?
Also, you mentioned that concrete is full of moisture. Wouldnt it be better to seal the wall first with a concrete sealing paint to prevent moisture from bleeding out from the concrete, then glue the foamboard to the concrete wall to prevent the warm air from conctacting the concrete, then put up the framed wall with fiberglass?
I just inspected a wall that had foamboard between the studs and the concrete. The foamboard was not glued to the wall, and the wall was covered with condensation (in winter), which was running down the wall and out from the bottom of the baseboard.
Sam – Poly = Plastic
Gluing it to the wall will only do one thing and that’s hold it tighter. Gluing won’t stop warm air from getting behind the foam, that’s accomplished by sealing the foam. You can seal the concrete but most of those products rarely work as advertised so it’s a waste of money and time in my opinion. Remember, with this approach we’re using the foam board as the vapor barrier. Water behind the foam will do no harm to it.
Putting foam board between studs doesn’t work. You need a continuous foam layer behind the studs. Putting foam between studs won’t stop moisture from getting behind.
Great video, have a couple of questions.
In the video when you showed installing one of the panels vertically, you had said to make it tight against the floor, and also against the bottom of the joist. Where the wall runs parallel to the joists, it looks like you stop the blue board at the top of the wall. And then you also talked about using the foil face insulation at the rim joist level.
In the article for basement insulation detail
(http://www.homeconstructionimprovement.com/basement-wall-insulation-detail/) you say to “Install rigid expanded polystyrene insulation from the slab up to the top of concrete (masonry) wall. Install the same insulation along the top of the exposed foundation wall and then up along the rim joist to the bottom of the sub-floor.”
Is it better to use blue board to top of wall, and along top of foundation, and then use the foil face for the rim joist area, or is it better to use blue board everywhere all the way up to the subfloor?
For the wall that is perpendicular to the joists, where you had the blue board tight from floor to bottom of joist, did you use anything for the top of the concrete wall and anything for the rim joist there?
Thanks in advance
Steve – I guess I could have been a bit more specific in the video huh? The simple answer is you want to completely seal from the basement slab all the way up the concrete/block wall, over the top of it and up the rim joist. I typically use XPS foam against any concrete and foil faced on the wood. Foil faced has a higher R value but it doesn’t interact with concrete well (it will deteriorate).
I hope that helps.
So the way you did it in the video then, where you used blue board to top of foundation, and also along the top of the foundation, and then use Foil faced in the rim joists?
What’s your opinion of putting two 1 1/2″ pieces of polyiso back-to-back in the rim joists?
Perfectly acceptable…good luck.
You indicated that sealers were for the most part ineffective for the intended purpose of waterproofing concrete or masonry walls. Yet I have talked with a number of contractors who swear by a ‘slurry’ admixture made by Xypex. Others have mentioned Drylock (have no practical knowledge of this one). If one is dealing with a retrofit situation, would not the purpose of a hydrophilic crystallizing waterproofer such as Xypex have merit in prohibiting wicking of moisture up the concrete and through the sill plate?
Jim – In some situations sealers can certainly improve the amount of water vapor that escapes from concrete. However, trying to plug leaks from the inside is like trying to put your finger in a hole at the bottom of an 8 foot high dam. The reality is that hydrostatic pressures will almost certainly surpass any chemical sealer. I’m simply suggesting that sealers are not a cure all for fixing basement problems and far too many people rely on them.
Thanks for the great video!!! I was not planning on insulating between the floor joists above the basement as shown (but not mentioned) in the video. Not a problem I hope?
I also was planning on just doing the foam board on the walls and no fiberglass between the studs. I think you mentioned that was okay if it met the code?
Thanks for all your replies to everyone. They are always very informative!!
Not a problem, that house has radiant heat hence the insulation in the floor above. You are correct on the no fiberglass as well.
On the rim joist insul……
My house has black roofing type paper run between the end of the floor joists and the outside brick.
I’m thinking you just leave it there as is and put the foil backed foam against it and foam as shown on the video?
That will work fine. Good luck.
I have had a flood in my crawlspace recently with all this rain and am wondering if I need to take the blue board down off the walls of the crawl and clean them with a bleach solution to keep mold growth between the blue board and the cinderblock crawlspace wall/foundation away. Also they were glued to the wall and now are not so much. Can I just wipe them down with the bleach solution and put them back up? Or do I need to cut off all the old glue before I put them back up? The Crawlspace is unfinished with a dirt floor with a 6 mil vapor barrier over the dirt.
You shouldn’t have to do anything unless there is another source of food for mold to grow. Do you see signs of mold growth?
Done the rim joists (among other things) lol
And I have my blue board ready to go.
Question do you do any rim insulation on the wall that is parallel to the floor joists? There is no real cavity there but just a 2×10 running parallel to joists. Maybe a small 2″ lip where it rests on the sill plate. So leave the wood bare or foil foam board in front of?
Similarly, in the rim joist area as shown in the video I have two windows that have a header on top. Therefore the space between the joists doesn’t just go to outside brick but has a 2×10 filling the cavity. Would you put the 2″ foil faced foam in front of the 1 1/2″
thick wood or use 1/2″ foam instead? Or leave wood bare?
One for the blueboard. If you have any gaps that are not tight, would you foam them than scrape foam flat and still tape?
Thanks again. Sorry to be long winded but without pictures I was just trying to be clear.
Not 100% clear on your questions. However, I’ll do my best to give some response.
– Ultimately you want every ‘exterior’ surface to be insulated. Sometimes the area between the rim joist and first joist (parallel) is quite tight and it’s difficult to insulate. Even if the space is tight you want to get as much insulation in there.
– You want to have insulation continuous from the wall, down the rim joist, over the top of foundation wall and then down the face of foundation wall. Visualize a continuous layer of insulation from the basement slab up to the attic.
– I try to insulate everything up to the window, then build extension jambs for the windows and insulate up to the jambs.
– Yes, you can fill gaps with spray foam.
Thanks for the help. (again)
I think you got me straight on the parallel joist question.
*** If there is say, a 1 1/2″ lip on the sill plate you would insulate that and be against the outside 2 x 10.
I know they have 1 1/2″ blue board. Should you use that there or can you stack 3 pcs. of 1/2″ foil faced foam?
I have only seen 2″ or 1/2″ foil faced.
Either will work…..R value is additive. Good luck.
. Thank you for the great video and article. I am renovating the basement that was poorly done and had to stop my contractors mid way :-) They were putting fiberglass straight to the foundation wall. Now, I won’t use boards but will go with a spray foam, got the steel studs up already, hard to bring them down. One question i need to ask though. I have a couple of storage rooms that have finished walls, but the floor is not finished – painted concrete. They are separated from the main area by dry walls I am rebuilding. If I insulate and finish the main area, what should I do with the storage rooms? I have no need in a laminated or ceramic floor there – do I have to seal the floor there as well so all the work to seal the main are is not a waste? Sorry, I am new to this
I think you can just keep them painted. The real issue now is being sure you monitor the relative humidity and use a de-humidifier if the humidity levels are too high. You want to be in the 50% humidity range which is typically hard to do in a basement without some sort of conditioning.
Thanks for the video…very helpful. Two questions, though.
You wrote: “Foil faced has a higher R value but it doesn’t interact with concrete well (it will deteriorate).”
I am looking at using Dow Thermax Sheathing to insulate my crawlspace. It is foil-faced on both sides, but Dow claims you should fasten/glue it directly to foundation walls. See here:
So, just wondering now what kind of deterioration you have seen with it. Have you used Thermax as opposed to Styrofoam?
Also, Dow and others mention leaving a termite-inspection strip of a few inches near the top of the foundation wall. That seems crazy in terms of insulation/vapor barrier. Seems like that would defeat the purpose of the vapor barrier. So, I’m not sure if I should follow Dow’s advice. Any thoughts on that?
Jack – If you look at Step 1 they suggest a vapor retarder or layer of poly. That is sufficient to protect the foil facing from reacting with the concrete. Aluminum will have an oxidation reaction when in contact with concrete which eventually leads to the breakdown of that layer. It’s not a huge issue but one that should be addressed.
The insect strip is important in areas where Termites are present.
Thanks for the video. One qustion. My basement walls (concrete) are wrapped with fiberglass insulation against the concrete and a layer of poly on the inside. Is it best to take this down and redo the insulation with foam board or can I leave it up, make sure it’s sealed and put up my stud wall next to it? Also, if I do the latter, should I put more fiberglass between the stud cavities for additional R value.
Absolutely. Please read the following articles which will give you some better detail and explanation. I DO NOT recommend fiberglass in direct contact with concrete. Good luck.
Thanks! Just one more question. My local store has 1 and 2 inch DOW polystyrene foam board. Two 1″ sheets cost less than one 2″ sheet. Would two 1″ sheets provide the same R-value and vapor barrier and the single 2″ sheet.
The two sheets will work just as well, it might be harder to work with though. Be sure the first layer is taped before the next.
Great Video. Actually, was able to comprehend exactly what I need to do to set up the basement walls except for one area. This would be in the rim joist area. My walls are concrete block. The top row of block is open. Should I lay a layer of foam insulation on top of the block then the rim joist taping the inside corner or try and just run the sheet of insulation all the way from the floor to cieling joist.
Glad it was useful for you. I hope you’ll consider signing up for our FREE Weekly Newsletter.
Your first assumption is the way I’d recommend. You want the foam to follow the cold surface up and over the top of the block and be continuous with your rim joist insulation.
I have installed 2” XPS to my unfinished walls. I’ve followed that up with framing the walls out (2×4). I have never been able to get a clear answer on whether I should use additional insulation batting within the 2×4 framing. What are your thoughts on this? If it is wise to use additioanl insulation, what type should I use (faced or unfaced)?
Thanks for your time
It really depends on what the code requires for R value and how well insulated you want the space. Unfaced is probably best so that it can breath.
Thanks for the input. I assume since you are using unfaced so it can breath, you wouldn’t need to use 4 mil poly sheeting between the batting and dryway?
Thanks again for all the help.
In that particular situation the 2″ foam board will be the vapor barrier. That’s the beauty of XPS foam.
I have a unfinished conditioned basement. Can I use dow commercial 2 inch tuffr directly on the walls? Also in a portion where the concrete meets a stud wall where there is already unfaced fiberglass bats can I put this product directly over this?
You can use 2″ Dow TuffR. I assume when you ask directly you mean against the concrete correct? I would NOT put this over a framed wall that has fiberglass, this should go behind that.
Unfortuneatley I am already two thirds done with the framing. The entire inside of the poured foundation was sealed first. I dont want to endure the cost and labor involved with re-starting this project, to include XPS. Also I rerouted most of the plumbing and electrical around the space, up close to the rim joist, making it nearly impossible to do the foam properly.
I understand the principles at work here..and the danger of using fiberglass wthout the foam……so at this point should i just NOT insulate ???? Or is installing sheetrock on wood an inch away from the concrete going to cause mold anyway ???
I’d HIGHLY recommend that you NOT insulate with fiberglass. You could use something like Rockwool…..but it’s likely that will hold moisture and eventually the studs will mold.
At the very least I’d use foam between studs. This isn’t perfect and still runs the risk of issues with the framing.
I am only framing half the basement, the other half is utility…..so half the foundation is going to be uninsulated anyway…..leaving it to its normal drying cycle as it has been for sixty years. I can only hope that by installing studs and sheetrock where I have, doesnt trap enough moisture in dead space to cause me problems. I will consult you in the future though…..long before a material list is made.
Good luck. Just remember, concrete looks like a sponge under a microscope. It has a vast network of micropores, tunnels and voids that are full of water for the entire life of concrete. That water comes and goes even after 60 years.
Thanks for sharing your project with us.
Todd about not putting fiberboard over wall with insulation it looks like in the video you did foam over fiberglass batts. I am a little confused. Thx mike
I meant foamboard not fiberboard. Sorry!
That piece of foam over the fiberglass is an exterior wood wall. It’s not a foundation wall. There’s a big difference.
Yes the wall I am talking about sits on top of the concrete wall with a small edge. It is an exterior wall and cavities are filled with unfaced fiberglass insulation. If I put the foam board (commercial tuff r foil faced)directly against the bottom concrete portion of wall can I also put it directly against the fiberglass filled wall which is an exterior wall. Also any recommendation as what to do with edge? Thx
You are correct. You can do that. I would cover the edge with foam as well.
Todd on the wall that I am talking about that is an exterior wall with unfaced fiberglass can I use something less than 2 inch foamboard?
You’ll need 1-1/2″ of foam for a vapor barrier. If you’ve got sufficient fiberglass, you can omit the foam on a wood framed exterior wall, just be sure to use a vapor barrier.
What type of Dow blueboard are you using in video? I cannot seem to find it at Lowes or Home Depot.Any suggestions?
There are several DOW products that are XPS. You can also use Owen’s Corning XPS pink foam.
Thanks for the very informative video. I am in the middle of planning to remodel our basement in the Chicago suburb. I have been researching a lot in Building Science website. There are a few questions I have with the studies from BS and hoping to hear your opinion. I understand there won’t be a single correct answer to this topic but this looks like a good place to start a discussion!
Initially, I was planning to use a 1” XPS (pour concrete foundation), combo half stud wall w/ Batt insulation w/ vapor barrier and cover all with 2×4 studs with Batt insulation to finish my basement. Then after the research I did with BS I have more questions.
(Warning: some variations not recommended) Can you help me out on it?
At this link they recommended using 1” or above XPS
My questions are am I Ok to stick with a 1” XPS all around? If some area in the basement where the spacing is too tight to have the 2×4 wall w/ Batt insulation than what would you suggest the minimum thickness for the XPS?
Thanks for stopping by our site. The building Science resource is a great help! There are many variations on this topic but most publications (including some of theirs I believe) are not recommending a minimum of 1-1/2 inches of foam. That is more important than the fiberglass. So at all costs get the thicker foam in there and then reduce the wall framing to 2×3 or 2×4 on the flat.
I hope that helps. Good luck!
Thanks for your reply. So, if I read you right then minimum I should install is the 1-1/2″ XPS in all concrete walls and then where spacing allows than I will put in the 2″x4″ frame with 4″ thick fiberglass? Yes?
You got it!
Thank you! One more question; I am planning to have a potion of the basement unfinished as a workshop. Should I warp the unfinished potion of the foundation with XPS? If so I will need to cover it somehow with minimum 1/2 drywall too.
If you can afford it I would definitely do that. It doesn’t necessarily have to be drywall, some 1/2″ plywood/OSB products also meet certain code requirements. If you’re building a workshop that would be a better approach.
I have a sub-basement which is completely below ground. We have never had any moisture issues. After much reading and research I decided to drylok the poured concrete walls. Next I began framing 4 1/2″ from the wall which left me 1/2″ to 1″ gaps between the framing and wall. On the first wall I put R13 paper faced fiberglass insulation in. For some reason I decided to check on it and noticed I had condensation on that wall but only where the insulation was. I removed the insulation and have decided to try this method.
My problem is I have half my walls up and I can only squeeze in 1/2″ XPS rigid foam. From everything I have read I do not want to put up a vapor barrier but I am not willing to tear down the walls I have completed to start all over. Any suggestions on this?
I also wonder about the fiberglass insulation the builder stuffed in the joists from the top of the cement towards the outside of the house. Should this be removed and sealed up with XPS rigid foam and spray foam? If I leave it up there you have nails from siding and pipes going in and out that can let moisture in which will eventually be absorbed by that fiberglass insulation. I am not really clear on how to handle this.
I planned on doing 1 1/2 inches XPS on the remaining half of this project since those walls are not up yet.
Finally will Liquid Nails for foam work? It says cement is ok but not sealed cement. Is Drylok considered a sealant? I think of Drilok as more of a bonding agent. Sealant makes me think of something you treat your driveway with.
Thanks for the great info. I look forward to your answers.
I’d recommend that you cut those walls loose….and slide them forward. You REALLY need to get 1-1/2″ foam back there.
I’d replace that fiberglass with foam.
That adhesive will work
Forgot to ask. Do you leave the plastic covering on both sides as well. If so couldn’t the foam board release from that plastic covering and come loose?
I noticed in the video the yellow fiberglass insulation. I have a few of those in pre existing unfinished walls and the builder put the paper facing out away from the room. I thought this always goes towards the room?
Are you talking about plastic on the foam? Just leave it, any adhesive you use it only temporary until you put framing up. After that it doesn’t matter if it moves so long as the seams stay sealed.
Your builder did it correctly. That video the fiberglass still needs a plastic vapor barrier.
Thanks again for your advice! This may be a stupid question but what method did you find is the most effective way to cut XPS? I have read on line ranging from table saw to extended length of a snap off razor blade! Any suggestion on it? Thanks.
Honestly, there are several ways that work well.
– Table saw (use dust collection if you have it)
– Circular saw (very messy but effective)
– Utility knife blade, much harder but cleaner.
I just bought the Owen Corning XPS pink foam and noticed there are pre-cut slits in it for easier cutting. If I am using the whole sheet, do I need to tape these 6 seams (3 on each side)? There is probably a half-inch of solid board between the pre-cut slits. I purchased 1.5 inch boards.
THank you in advance for any suggestion.
Tom – I haven’t used that kind before. In a perfect world those cuts wouldn’t be there. If you want a belt and suspenders approach you’d probably tape them. Is it the end of the world? no.
Great video. I just bought a new construction house and am preparing to start finishing the basement. I would like to install rigid foam board onto the walls but I have a problem. Most of the areas on the wall where ties were used have a lump of concrete about the size of a golf ball so there is no way I can lay the boards flat.
I live in New Hampshire btw….
Which would be a better option:
1) Attach the rigid foam to the back side of my walls. Build the walls so that the back of the rigid foam is just far enough off of the wall to clear those golf ball sized concrete from the ties. Use fiberglass to fill the 2×4 studs. No poly vapor barrier at all. Drywall over that.
2) Build the 2×4 walls keeping them several inches away from the concrete wall. Fill the voids with fiberglass but making sure that the fiberglass does not touch the concrete wall. Attach a poly vapor barrier and drywall over that.
Thanks in advance.
Jason – Those “bumps” are very common. We always break them off with a hammer. Then follow the details in this article: http://www.homeconstructionimprovement.com/how-to-insulate-basement-walls/
You HAVE to use foam, using just fiberglass is a perfect recipe for mold.
Hi Todd I want to insulate my basement floor with foam board then put a sleeper floor on top 2×4 pt 16 on center then osb board on top is that a good idea and if so how thick will I need for the foam on the floor minimum because of clearance?
Or maybe do you think 2×4 pt 16 on center foam between the. 2×4 then osb board to save the clearance?
CHeck this out John. http://www.homeconstructionimprovement.com/how-to-insulate-a-concrete-floor/
That was great todd thank you one more thing no poly under the foam or over it does not recommend do to the foam board?
You can certainly put a layer down under the foam if you want. However, most modern slabs have a vapor barrier under them.
Thank you reading your other comment with other really help
I have been trying to install XPS 2″ sheets the same way you show how.
the problem I am having is adhesive? I have tried about four different ones none of them seem to work well do you have any ideas. My walls were painted once in the past by the past owner with drylok I do know that all four said don’t use on painted or coated surfaces. Alos why should I leave a 1/2 to 1″ space from the XPs and the 2×4 wall? I am also planing on using rock wool insulation unfaced in the 2×4 what do you think of that?
Thanks For Your Help
Keith – Adhesive isn’t absolutely necessary. In many cases we cut it so it fits tight top and bottom and doesn’t move. The air space is nice because it allows for air movement, again not 100% necessary but a nice to have detail. Rockwool is a great choice. Good luck.-
Sorry I also wanted to tell you that I have green board from lowes 2″ 4×8 seems glue up ok with some bracing but I have a wall that is 56′ long and have tried to install 2′ 2×8 owens corning T/G thats the stuff that just does not seem to adhere to the wall. The lowes green board seems great it also seems to be less pliable also.
Thanks For Your Help
Thanks for the helpful articles and info. Need some advice on the basement project I am about to begin.
Currently the space is “unfinished” with a few caveats. The foundation walls are 8 feet high of block on three sides of the foundation. The forth side is across the entire back length of the basement and it consists of 4 feet of block foundation then 4 feet of wood framing (much like the left wall shown in the video). The 4 feet of framed wall is “finished” (insulated with fiberglass batting and has been drywalled). I’m pretty certain the builder and previous owner just intended to never insulate the block portion which I just don’t understand.
So, should I pull down the drywall and put up XPS from base of floor to the joists including over the wood framed and insulated portion like you show in the video then build 8 foot 2×4 wall. Or should I just leave that upper half alone and only worry about putting XPS on the 4 feet of block and build a half wall instead of a full wall? Seems to me it would save a lot of time and material costs to just do the half wall since the top portion is already done, but I don’t want to do it wrong or cut corners just to save some time and money. I rather do it right and do it once.
Also, do you think we should put down 1 inch XPS on the floor covered with plywood or could we get away with simply putting down the carpet directly to the concrete? (located in KS) If we should put down the XPS on the floor, do we do that first and then build the walls on top of that or do we do the foundation wall work (2 inch XPS & 2×4 wall) first. Common sense says floor first but just thought I would ask while asking.
Steve – Sorry for the delayed response, things have been super busy around here.
Most likely you can keep what is there and just do the un-insulated portions. However, before you go that route, I would recommend you cut a small test hold and check the insulation. Be sure there’s no mildew, mold, or moisture in the existing area. If it’s nice and dry then I’d leave it alone.
The floor issue is really a preference thing. Obviously if you insulate the floor it will be far warmer. However, insulating the floor can create expensive issues that might not be worth the outcome. For example, the added height will mean moving doors up to allow for the height, you might have stair issues at the bottom riser. JUst be sure you think it all out before you make a decision.
Todd, what other insulation can be applied between the studs after the foam board has been installed. Also, I have my discharge plumbing pipe thats runs horizonal against the back wall and i have to frame that wall in front off it, which leaves a 4 to 5 inch gap space. Should that space be fill before i put up dry wall.
Mark – ANother option is using a product like “Rockwool” which is not only fire resistant but it’s also completely mold and mildew resistant. You can leave the space open which helps dry things out if it ever gets wet back there.
Great video! I have learned a lot from the video and your comments.
I live in the Portland, Oregon metro area. My house was built in 2007 on a slope of over 16′ from the front of the house to the back. I have recently added a room under my garage in a space that was left empty by the original builder. The room is 560 sqft and has a 10 foot ceiling. The floor consists of 1-1/8″ plywood over TJI floor joists. The room is to be used as a workshop with no HVAC. I would like to insulate and drywall the room. Three of the walls are above ground.
My question is concerning the fourth wall, which is under the driveway. This concrete wall is 10′ high. In the four (4) years that I have been planning for this room, I have never seen any water on the wall or noticed any moisture in the 16′ high “crawl space” (which is now the workshop). Since the concrete driveway is directly above the fourth wall, and the driveway slopes to the street, I assumed that the driveway would keep any significant water from ever getting to the wall. Then I watched your video and read your comments….
The concrete wall has a structural load bearing wall [consisting of 2×6 PT (pressure treated) studs and plates] adjacent to it. The original builder did not leave enough space between the stud wall and the concrete wall to put anything more than a sheet of poly between them. In some places, the poly won’t even fit, because the stud wall and concrete wall are touching.
I have gotten bids for moving the stud wall away from the concrete wall, but you can imagine the quotes I am getting are in the excess of $10,000.
Do you have any other suggestions? Should I even be concerned? A couple of contractors have suggested just using Drylock or some other sealer product.
Thanks in advance for your help.
any chance you can email me some photos? if so send them to
todd “at” frontstepsmedia dot com
I have a question regarding finishing my basement. First and foremost I plan on creating a insulated sub floor. I know a lot of people do foam board-sleepers-ply-finished floor.
I was curious to know if doing 2×4 pt sleepers directly on the concrete and then inserting foam boards between the sleepers then ply and finaied floor would be sufficient and hold moisture back and keep the floor warm. Is a vapor barrier needed on top of the sleepers and foam?
All of this because I want to build my walls on top of my floor to have a nice level surface throughout and insulated
Alex – The trouble with doing it that way is you lose the “vapor barrier” and you don’t have as great of a continuous insulation layer. If you use that approach be sure to use a vapor barrier as well.
Hi, I had to remove my dry wall ,fiberglass insulation and studs due to mold. I made the mistake of installing the studs and fiberglass insulation against the painted concrete walls. This caused the condensation to soak up into the insulation and cause mold to grow on the concrete walls and dry wall.
I now plan to install 1.5 inch XPS foam then frame the walls ,then fill with unfaced fiber glass.( not going to use a vapor barrier)
My question is I had mold growth on the painted concrete wall. I killed it with a bleach solution and spreyed a mold inhibitor on the paint. Is it now safe to install the XPS against the concrete block?
Ron – You should be all set now. XPS won’t be bothered by mold or water so either way you’re all set.
One other thing …. My water meter is in the corner of the basement. Last go around I just mad a book shelf to hide it. The inside was open with insulation against the wall. But of corse the meter condensed like crazy. Any suggestions on how I can avid the meter from condensing?
I would insulate behind it with foam board. Then bump out the wall around it, insulate that wall as well, so basically the water meter is inside a foam box. Be sure the box is air tight and the it won’t sweat.
Should I pant the wall with a mold/mildew paint before I install the 1.5 inch foam since there was mold previously growing on the wall?
Or should i just install the foam and start framing?
Im trying to avoid what went wrong the first go around.
Ron – I can’t hurt to clean it and paint it. However, it’s likely not an issue because the foam board won’t promote mold growth by itself.
I started installing my XPS foam board. One thing i noticed is the the concrete floor is not level. There is a bout a 1 inch gap at the bottom of the board. I tried to keep the foam level and the butt joints tight. Should I use the spray foam to seal the gaps at the bottom or try to tuck small pieces of foam board under there?
I would just fill the gap with spray foam.
Great Todd, Thanks finished up the basement. All is back to normal now!
Hi Todd excellent informative video. I am in the info collection stage for doing over my basement. I am in Mass which gets pretty cold. Which to you would be better to insulate the concrete walls with? I have issues with The Owens Corning Company, so I would rather use another brand if possible.
Owens Corning Foamular F-250 2 in. x 4 ft. x 8 ft. Tongue & Groove Foam R value 5
Poly Shield 2-in x 4-ft x 8-ft Expanded Polystyrene Insulated Sheathing R value 7.7.
Using the Poly Shield would save over $400, but if it isn’t as good or isn’t the right product, then the savings means nothing. I’ll just spend the extra for Owens Corning if you think it is worth the spend.
Nick – Thanks for the compliment. The Polyshield is just as good of a product and it has a higher R value…..decision made. Good luck!
Thank you Todd. One more thing. I have batt insulation currently in the rim joists, i will repalce that with foil faced and sprayfoam around it. My question is, I then have 4-5 inches of concrete on the sill exposed. I can put Polyshield over that but if I then add a vertical piece from the basement floor all the way to the floor joist i can’t reach behind and seal the piece on the sill to the vertical piece I just installed flush to the concrete wall. Is there a way to do this easily that I am blanking out on? Also, where the Polyshield and the concrete basement floor meet, should I sprayfoam that seam along the entire perimeter?
Nick – There are many different ways to do this. One way is to run the wall insulation (the main concrete wall) up to the top of the concrete. Then you can run a piece over that and over the concrete. Tape and/or seal all those joints. Foaming the bottom isn’t necessary. Good luck.
Todd, great information. I am hopeful you can set me straight on my dilemna.
I am about to finish my concrete block basement. I have an interior french drain to a sump well, weep holes in the bottom of the wall, and I and have recently dryloked the walls. I was about to adhere 2″ xps to the block wall, then 1″ xps to the floor, glue and tape all seems and spray foam all gaps. Then, was going to put 3/4″ osb on the floor, then frame flush to the wall with 2×4 framing. No additional insulation, and then mold resistant drywall over top.
After reading your articles and posts, sounds like I am better off leaving a 1″ gap between the xps and the wall, and not frame right against the foam. Correct?
Wat are your thoughts on dricore panels as the subfloor, instead of the xps and osb? The xps has a good R factor, but the “direct contact with slab” theory is in contrast to the airspace theory pf dricore, delta-fl, etc. R factornaside, does one provide mold resistance better than the other?
I planned the put the subfloor down before framing, then tapcon or hilti nail the bottom plate through the floor to anchor to the concrete. Is this a good plan? Or should Use a PT bottom plate with a thin foam cap break, and get the walls framed before I out the subfloor in (if I go with dricore)?
I will be finishing 75% and leaving 25% (sump well, furnace, water heater) unfinished. I will have a dehumidifier in that area, so does this change anything abiut my plan? Should I leave an inch of airspace between the block wall and the xps/studs, to let the air circulate behind the wall? Or must I have direct contact with the wall, to accomplish a vapor barrier? Either logic can make sense to me depending on how I rationalize it, so am appreciative of your feedback.
Thanks for some great content.
Paul – Thanks for the kind words. I’ll try to hit most of your questions below.
– The air space isn’t necessary. I recommend it when additional fiberglass is being used and when it’s a basement that has a history of being wet. This really wouldn’t apply to your situation from the sounds of it.
– I’ve used Dricore and it’s a good product. However, you give up some insulation value. I think either approach is good. If you have any thought that you could get water in the future then I’d use dricore.
– The vapor barrier has nothing to do with the space. The space is just insurance to help dry things out in case of water.
Thanks Todd. To confirm when you say “the space is added insurance”, I’m picturing XPS I direct to the wall, then the 1″ air space, then the stud wall. Is that correct, or is the airspace between the concrete wall and the XPS?
You are correct.
Thanks again. One last question if I may…
We had a major thaw this week, and the drylok helped considerably on the walls. A drop of dampness here and there, but for the most part all of the water moved down and out through the weep holes which are an inch up from bottom of block wall. They were drizzling water into the interior perimeter drain system pretty steady during peak thaw. That made me think…
Should I adhere the xps foam right over the weep holes and seal it down the floor, or should I cut the xps a bit short short and seal the bottom of the xps sheets to the wall just above the weep holes (leaving the bottom inch of block wall uninsulated, but unobstructed water flow from weep holes to french drain?)
My friend is helping me with this project, and he may have already asked this. I scoured your boards for his post, but didn’t see it. If I missed it, apologies for the redundancy. We have learned a ton from your website. We have done our research, and this is the single best resource we have found on this topic.
Paul – Certainly a great question. The answer is…..there is no good answer. Basements like yours always run the risk of issues because you have “active” water events. Having said that I would probably modify the bottom of the sheets slightly. I would cut a 1/2″ thick piece of the foam from the back of the sheet to create a “channel” where the water can drip out of the hold and run down the wall to the drain. Be sure the sheets are well sealed to each other and the floor below.
Good luck…thanks for the compliments.
Great video and very informative. My basement is a block wall that sits below grade then wood studs which are above grade that sit on top of the block. My plan was to use 2″ of foam board over the block wall and build a wall with unfaced insulation over it. I was only going to go up about 4 feet to where the studs sit on top of the block and create a shelf in the basement. Would this be a proper installation?
On the studs that are above grade I was planning on using fiberglass insulation then drywall.
Jason – It will work but it’s not the best solution. Basements are so damp that I’d rather see at least a 2 inch layer of foam in the stud cavity before fiberglass. This is just another good layer of protection but one that I feel is worth it in basements.
The more research I do the more thoughts go on inside my head, which isn’t good lol. I have read that using a 2 inch foam board with a water vapor permeance of 0.1 or less will also quality as your vapor barrier. With that said, I have read to not then add another vapor barrier behind that. I was thinking of just using a Thermax Sheathing, 2 inches thick, R-13 value and 0.03 water vapor permeance on the foundation then tape and seal all joints. Stud the walls in front of this. My question is about the wall cavities. Do I need to insulate them or is the foam board R-13 value good enough? If I do need or want to add something to the wall cavities what should I use?
Does the paper backed insulation create a second vapor barrier that I didn’t want? If i use unfaced, how do i keep it from sliding down the wall cavities?
The 2″ is a great start. Depending on where you live you may need more R value to meet current energy code requirements. Obviously the more you have the more energy efficient your home will be. In a situation like this, if you tape the foam really well, have a mostly dry basement, then paper faced is fine (I would cut some holes in the paper just to be safe). Unfaced can also be used, it will likely stay in place if its cut snug tight.
Hey Todd. Appreciate all the knowledge! My local store sells the foam board in 1 3/8 inch. Should I be concerned that its not quite 1 1/2 inches? Or am I splitting hairs? Thanks!
Rich – What brand/kind is it? I’ve never seen that dimension before, makes me think it’s NOT XPS foam. Sure it’s not some kind of open cell product? The industry standard is 1-1/2″ minimum, typically we use at least 2″.
I was going to use this product in 1 3/8, but I found it in 2″ (link below).
Should I use this product?
I was also thinking of not insulating at all and heres why. Its a 100 year old house in north jersey, that has no insulation in the entire house. In this situation, would it be a waste of time and money (approx $1,000) to insulate my basement when the rest of my house is not insulated? And if I didn’t insulate, can I just fasten 2x4s to the basement walls and then drywall? Thanks again for all your help. Much appreciated!
That is a good product. I do not recommend framing walls and drywall without dealing with the moisture.
For lack of a better term, my concrete basement walls are very slightly “wavy.” So when I adhere my foam board to it, most of it will be flush making contact with the wall, but parts may be around 1/8″ or 1/4″ off the wall. Is this a concern or no biggie?
One of my basement walls is 100% above grade (adjacent to an attached garage). It is concrete and my basement does get damp in the summer, but again the entire wall is above grade. Can I use fiberglass on this above grade wall only?
Lastly, my basement floor has already been built up about 3 inches with flooring installed, so I wont be able to get to the bottom few inches of my wall when I install my insulation. Any concerns there? Thanks Todd. Love the video!
Kim – No worries about how flat the wall is. 99% of concrete walls are just like that. The key here is how well you seal the adjacent sheets of foam. Yes, you need to use foam on all the concrete walls. Again, those walls are full of moisture that will eventually get out and get trapped in the wall if it’s not sealed off.
Ideally you’d cover all the concrete. In your situation that’s not possible. Seal things as best you can.
Thanks Todd! I don’t think this question was asked yet. When insulating using the method you detailed, is mold resistant drywall still recommended/necessary for the walls and/or ceiling? Or can I just use standard (and less expensive lol) drywall? If it matters, my basement does get humid in the summer and my dehumidifier gets a lot of work. Thanks again!
Kim – Is it necessary? No…is it a good idea? Yes.
Before installing the foam board, should my first step be to use a sealer (such as Drylock) on the concrete walls? Some people swear by the stuff, while others say its a waste. What say you?
I think it’s a waste….once concrete cracks it’s useless IMHO
Hey Todd last question I promise! Will XPS foam boards in the rim joists be just fine or does it have to be the foil faced polyisocyanurate?
XPS is fine……just not as good with respect to R value
Should I be worried about XPS, drywall or ‘greatstuff’ being close to a steam pipe or a radiator?
In general terms no, however, foam board should be protected against flame as required by local building codes.
In our basement we have a 2″ trough around the perimeter of the basement floor, which drains into the sump pump hole. We do not have a water problem at all. I was wondering if I am supposed to put the foamboard insulation directly on the basement floor or do I leave it off the floor a bit to leave the trough exposed just in case I ever get water in the basement, as to not block the drain channel. Also, once studding out the walls, do I place the pt plate directly on the floor or should I leave a spacer every so often, as to keep the channel open? Thanks, great video
Bill – The foam can sit on top of it, water will still find it’s way under to the drain. It it were my preference, I would move the new wall just outside the drain and not cover it up. Good luck.
When I put up my stud wall over the foamboard, am I driving nails through the upright studs and xps and into the concrete wall? Or is there a method you recommend?
Also what are your thoughts on this product? Seems like an easy way to do it.
Rich – It depends on how you frame the wall. If you use traditional framing then no, the wall stands on it’s own in front of the insulation. This is the preferred method. However, if cost and/or space are an issue, you can use the system in the video. In that case, you’ll need to nail/screw through the framing into the concrete. That method isn’t as good because the nails/screws penetrate the foam/vapor barrier.
Hey Todd if I wanted to maximize space, can I glue drywall directly to the xps in lieu of building out a 4 inch stud wall? Thank you
You could try…I highly doubt it would be very successful.
Todd, great information! I read through the questions/answers and didn’t see anything regarding the use of poly against cinder block walls?
I also have 13 block high walls, 8 1/2 feet from slab to the floor joist. Would I just install an 8 foot piece and a 6 inch piece to complete the vapor barrier? It won’t be tightly fitted like you recommend.
My basement is mostly below grade and some small sections are dark like water is wicking through the block. I’m going to do some additional grading away from my house, but will these wet spots create a problem?
Last one….the expansion joint around the slab is about 1.5 inches wide, do I worry about this or just install the 2 inch thick board and foam seal it to the slab?
Thanks in advance.
Mark – Thanks for the compliment. Poly should never be used in a basement, that’s my first and most important rule! When it comes to the height, you can certainly piece it together, the easiest thing may be to glue a small piece along the bottom, let that dry, then install the upper sheets tight to the framing. The wet spots themselves are not a problem, but do be sure there’s not a large leak involved. The joint is not a problem. Good luck.
To follow up on my question.. In part of our basement we may want to build in shelving within the framing.
Our plan would be to put thin plywood directly against the foam-board with a little glue, then further secure it to the wall with 2×6 framing in front of it creating a built-in shelving unit?
So the wall/built-in shelving will be secure, but the million$ question is, does there need to be a few inches of space between the foamboard and the wall we create or can it be right up against it?
Thanks again Todd!
Kim – No space is required so long as you seal the foam really good. Sounds like an acceptable plan. Good luck.
Hey Todd, great video and I can’t believe you are still answering questions for a few years now! Thank you for that, there is much to learn here. I live in Toronto, the house is 30 years old, in the basement there is a plastic covered blanket insulation that has fiberglass inside. It goes around the first 4 feet of the basement walls, and below that there is no insulation just foundation walls. Can I take off the plastic vapour barrier, leave the fiberglass insulation that is about 2 1/2 inches thick, put on 2 inches xps over it to act as a vapour barrier, or do I have to take the fiberglass off and apply the xps to the concrete? Hope I explain this well :) Thanks again Todd for taking the time and answer the many questions here.
Brian – My pleasure, all I ask is that people LIKE our Facebook page, share the site on social channels, anything to help spread the word so we can make the site bigger.
Living up in Toronto you really need a good insulation system. I’d highly recommend removing that old blanket insulation and getting rid of it. From there I’d start over, install at least 2 inches of foam, stud the wall and install additional insulation to meet what ever minimum insulation value is required there by code. Best of luck!
Here’s another reference.
Todd – Thank you very much for your prompt reply! I will definitely like your Facebook page! Last 2 questions, after I install 2 inches of foam, stud the wall and install batts, by the way, is Roxul better than fiberglass for basements and do I need to install a Polyethylene Vapour Barrier before I install the dry walls? Thanks for the video reference! Take care.
Roxul is certainly a better upgrade. NO POLY :) Poly should never be used in a basement ever.
Todd, thanks for your reply, I viewed several of your videos, learned a lot and will be doing what you recommend for my basement. Take care.
Thanks to you, or basement renovation is coming along great.
Quick question for you: We have a cement block wall separating our unfinished basement from our soon to be finished basement. Our unfinished basement has our furnace in it and the door between the 2 rooms is usually open. My point is, there is not much of a temperature change between the 2 rooms. When I pulled back the old wood paneling, the framing is already in place. Considering the circumstances, can I just secure the sheetrock to the framing and bypass the foam board insulation for this one part? Its only about 4 feet of wall anyway. Thanks Todd!
Rich – That is fine, a block wall like that with air on both sides typically isn’t a problem. Glad to hear things are going along well. Good luck!
Great information for us DIY’ers.
My question is about airflow. My furnace is vented through the chimney. I have 2 windows that I’d prefer closed and i’m in the Northeast so in the winter closed is the better option! My HVAC duct work is from the attic down so I can’t get to any of those runs. Any ideas on how I can get some air exchange in the basement? I was thinking of doing a Mitsubishi Mr. Slim unit but that will only bring in cold air not exchange the air i believe.
Nick – You might want to consider a small ERV (Energy Recovery Ventilator). You can vent them through a wall. We are using more and more of these on new homes now.
Great information to have. What’s your thoughts on steel studs in your application. Pros/Cons.
Glenn – Steel studs work very well, really no different than a commercial building application.
The more I read the more baffled I become!!
Some strongly advocate letting the interior concrete wall air in (for moisture relief), others strongly advocate sealing the interior wall with foamboard mounted directly to the concrete.
My present proposal is to either fix 2 inch Thermax directly to the concrete wall, or alternatively to fix XPS to the concrete, then cover with Thermax.
Additional info: Home is recently built with poured concrete basement that has exterior “membrane” for moisture, and appears totally dry.
I had originally figured to leave and air gap (3/4 inch) between the concrete and the Thermax but was advised this would create a mold risk.
Would appreciate your comments very much. Thanks.
Chris – Insulating basements is one of the harder building science topics to get right! First off, I’d also suggest reading this article: http://www.homeconstructionimprovement.com/how-to-insulate-basement-walls/
Concrete doesn’t need to dry, in fact, it never completely dries, and water is good for concrete (it’s a chemical reaction between portland cement, sand, stone and water). So there’s no need, nor any reasonable way to dry it out. What is important is keeping that moisture from getting into the finished framing and finishes in a basement. The best approach is sealing it off with a permeable insulating layer that stops moisture, and won’t transfer the cold/cool temps of the foundation wall. That’s why products like XPS foam work so well, they stop vapor movement and they won’t transfer the cool temps so moisture on the other side doesn’t hit a cool surface and condense.
I don’t like to install a product with metal facing directly against the concrete as it usually reacts with the cement, XPS is much better suited for direct contact.
When using 2″ XPS board on the walls, how far must I stay away from flue pipes that go thru the wall. One pipe is conventional 24 gauge for a oil boiler and the other is a triple wall pipe for a wood burner. With foam on the wall and metal studing and then drywall, what would the clearences be behind a woodburner? Thank you, I really like your website, so much fantastic information.
Joe – Flue pipes are certainly something to be aware of. Honestly, I’d keep a pretty significant distance away and use a fire resistant material like Roxul near those pipes. Be safe!
Would appreciate your help, your guidance is excellent!! Best one found.
I am a retired senior citizen who has decided to take on a basement project. I am slow as molasses, but, will get it done. :)
Have a basement with block walls, and need to build a small room (9’x 8′). The room will go in a corner of the basement. and, will place a framed wall directly in front of the foam board.
You mention leaving an inch gap to allow for air flow around the studs, and, in my ignorance, I got confused on this. Somehow thought the frame with the studs is supposed to help hold up the foam board to the basement wall blocks, and that we need not worry too much about how the foam board is attached to the block wall.
If we leave an inch gap between the foam board and the wood frame, couldn’t that give the foam board some room to move away from the block wall?
Thanks in advance for your help!
The inch gap isn’t necessary. We do it both ways, if we don’t glue the foam, we put the framing tight. The foam does not need to be tight to the wall, it just needs to be sealed well. Good luck!
Todd. First of all love your site, lots of good info. I have stairs that follow an exterior foundation wall to the basement. The stairs are three feet wide and make a turn at the bottom. What is the best way to attach foam to the wall and achieve a decent R insulation rating, without losing too much stair space. It is a tight fit going down the stairs as it is. Also there seems to be a mold issue at the bottom of the exterior wall where it meets the concrete foundation in the stairwell. Thanks.
Don – Thanks for the kind words. This is a really typically situation that doesn’t have many good solutions. In most cases I’d like apply some dampproofing paint and call it a day. Loosing width on the stairs stinks and there’s no good way to get the insulation behind the stringer adjacent to the wall, so in my opinion there’s not much sense in doing it. Ideally you’d reframe the stairs after insulating against the wall, but that’s just not feasible in most situations.
I would try to deal with that mold issue for sure. Needs to be cleaned properly and hopefully sealed with products to stop that from happening again.
I love the site, very informal.
Quick questions, should i put drylok before I put the Foam boards on the walls.
I’m thinking of doing epoxy floors, so do I do anything with the floors for mold/moist prevention?
It can’t hurt :)