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Basement Insulation
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” 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.
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:
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.
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.
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?
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.
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.
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.
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.