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Old 10-04-2012, 07:09 PM   #1
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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?

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Old 10-05-2012, 08:05 AM   #2
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Rigid foam and fiberglass


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.

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Old 10-06-2012, 11:15 PM   #3
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Rigid foam and fiberglass


Check locally, and starting on pp.15; ftp://ftp.cmhc-schl.gc.ca/chic-ccdh/..._Web_sept5.pdf

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Old 10-07-2012, 09:33 PM   #4
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Rigid foam and fiberglass


Thanks, an interesting read yet once again, never a straight answer.
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Old 10-08-2012, 09:58 PM   #5
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Rigid foam and fiberglass


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

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Old 10-08-2012, 10:38 PM   #6
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Rigid foam and fiberglass


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; http://www.buildingscience.com/docum...study-analysis

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