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mrtn 10-04-2012 06:09 PM

Rigid foam and fiberglass
I have been doing a ton of research and thought I finally had my plan. 2" xps rigid foam against the concrete, framing against that, fill 16" space with fibreglass insulation, then dry wall. Then I read on another contractors forum that I need a vapour barrier before I put up the drywall. I never really thought of it, but after reading more I'm getting conflicting ideas.. Typical. What are the opinions? Isn't the 2" foam good? Or because I'm adding insulation do I need a vapour barrier on the warm side? I thought this would trap moisture in between?

Windows on Wash 10-05-2012 07:05 AM

Depending on the foam, this would create a vapor trap.

While it may not be code, I personally think that the method you are looking at is the more proper and will keep the inside of that wall assembly warm enough that condensation will be a non issue.

Make sure the drywall layer is completely air tight and maybe use and air barrier like a tyvek and you should be fine.

Bulk air loss moves 50X as much moisture as does diffusion so if you stop that, that is what will keep the walls dry.

Gary in WA 10-06-2012 10:15 PM

Check locally, and starting on pp.15;


mrtn 10-07-2012 08:33 PM

Thanks, an interesting read yet once again, never a straight answer.

Braddiy 10-08-2012 08:58 PM

i have read conflicting reports as well the first one being that foam/rigid insulation is your vapour barrier then i read that this creates a moisture problem from lower basement wall to the top portion of basement wall. condensation caused by temperature changes and trapping the moisture.

sign confused!

good luck:furious::furious::furious::furious::furious:

Gary in WA 10-08-2012 09:38 PM

Unless there is plenty of foam air-sealed to the concrete wall, a vapor barrier/retarder is not needed. I have many links, all different (other than no vapor barrier) but just leave you with the best one. Find the different wall compositions and read about the vapor/moisture for that specific wall. The front part links to the back half;


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