I doing a basement remodel( 8′ below grade) and I’m looking for the exterior walls (against block) to be as thin as possible. To accomplish this I’m looking at closed cell insulation. The block wall is very dry. (I taped poly to a portion of it for 1 month, and no moisture appeared) It’s drain tiled, dry floor, etc.The foundation was foam sealed on the exterior with an R-5.
Can the polystrene insulation be applied directly to the block. Between Green treated 2X2’s? I’m looking @ 1″ insulation. Is it better to sandwich the insulation between say furring strips and the block. Should I put a vapor barrier over the block. What is the advantage of “foil faced” and why does “bead board” get a bad rap?
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Bead board is the same stuff that coffee cups are made of.. not a great insulator compared to the closed cell stuff.. The pink/ blue or whatever foam that you can buy at the lumberyard has an R value of 5 per inch while EPS has a r value of only 4 per inch.
foil faced has the potential to reflect infrared rays not something I'd worry much about in a basement.. As for putting a vapor barrier over the block why not? you can buy a roll of 5 mil. poly for about 50 bucks and tape it in place and should there ever become a problem with water you'll have one last line of defence. local codes will give you the final word on it's requirement. You'll need an inch and a half thick foam in your application.. 2x2's are actually 1 1/2 thick by 1 1/2 wide. your walls will be that much more sturdy if you fill them with foam.. if there is a half inch air gap between the foam and your block things will get a little flimsy..
It is best if you can apply continuous foam against the block walls without interruption. Caulk and tape the seams between the polystyrene panels. Both XPS and EPS are fine. EPS has slightly less R-value but it breathes more than XPS which *can* be good in some situations. In general don't use foil faced insulation because the wall needs to be able to "dry to the inside." If your wall is very flat and plumb then you can attach furring strips by nailing through the foam but it is better to build a wall just inside or against the foam. You can use 1 5/8 inch steel studs or 2x3 walls to minimize the thickness. One inch foam is fine if you already have foam on the exterior of the walls.
But first read the basement insulation details in the web pages below:
http://www.buildingscience.com/housesthatwork/default.htm
And especially read this once it is "re-published" to the web. It contains a wealth of information (I wonder what they are revising???):
http://www.buildingscience.com/resources/foundations/basement_insulation_systems.pdf
Edited 1/17/2005 2:14 pm ET by Billy
Edited 1/17/2005 2:16 pm ET by Billy