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dtran 07-08-2009 05:45 PM

Best way to insulate basement in cold Canadian climate

I hired a contractor to finish our basement but I want him to do it in a good way. Our foundation wall is not insulated on the outside and the basement is just over halfway underground. I asked him what he was going to do, and he said he was going to use batt insulation in 2x4 24" OC studding with vapor barrier going behind the frame, down and up on the interior side. From all my reading around the net, this method is commonly used, however is not recommended.

I hear a lot of people recommending to use rigid foam (at least 2" thick) attached right to the interior foundation wall. Is this the best way? If so, I have some questions:
1. If I used 2"-2 1/2" of at least R10 rigid foam, would you recommend using batt insulation still?
2. Do you still have to frame the basement to attach the gyprock to?
3. Whether or not you use batt insulation in combination with the rigid foam, if you frame the basement, do you need a vapor barrier behind the gyprock if you use rigid foam?
4. How do they compare cost wise using rigid foam vs batt insulation with vapor barrier? I would assume using rigid foam would be less labor intensive and possibly eliminating the cost of buying vapor barrier.
5. Reading the buildingscience PDF, they say the method of putting vapor barrier on both sides of the frame is not recommended because it doesn't allow the below grade foundation wall to breath to the inside as it cannot breath to the outside. But wouldn't using rigid foam also block the foundation wall from breathing to the outside as well?

Btw, I've read the building science PDF on insulating a basement, but I still have these questions.


TooledUp 07-08-2009 07:48 PM

What about foam insulation?? This stuff is great and your can seal off all air flow with this stuff. They can spray up under your sill and really seal off any air infiltration. They put about 3" of foam in a 2x4 wall--as far as a vapor barrier--I would check about using a vapor barrier with foam. You get about a 7 R-value with every inch, but after 3" the bang for your inch of foam starts dimishing. I was told 3" was optimum.

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