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Old 07-28-2014, 07:52 PM   #1
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double vapour barrier in Canadian basement wall


I'm in Ottawa (Canada) where it gets super cold in winter. I've started doing some wall repairs in the basement of a 1960's bungalow, and when I took some drywall down, I saw that there was a plastic vapour barrier on both sides of the pink insulation. One layer of poly behind the 2X4 studs, against the concrete foundation wall, and another layer on the front side, behind the drywall. The pink insulation was in effect, encapsulated in plastic. This can't be right. A vapour barrier usually goes on the warm side only. My question is this: should there be anything at all up against the concrete, like tar paper, or whatever? The studs BTW are slightly less than an inch out from the wall, so that's a good thing. I've pulled the inside vapour barrier out. Now I just need to re-do the wall that I've opened up (properly). Thanks in advance.

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Old 07-29-2014, 05:07 PM   #2
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double vapour barrier in Canadian basement wall


I use foam on the walls, I've never put anything else between it and the concrete. You'll want get rid of the air gap behind your insulation, sprayed foam is an easy way to accomplish that(unless you want to rip out the studs and start over)

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Old 07-29-2014, 07:23 PM   #3
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double vapour barrier in Canadian basement wall


Yea, I'd like to use spray foam, but I've only opened up a part of the perimeter wall, not the whole thing. To do spray foam properly, I'd have to rip out all of the drywall in the basement, and that's not happening. I guess I'm just going to re-install the fibreglass batts, and vapour barrier the inside (warm side) only. BTW, why do you suggest eliminating the gap behind the insulation? Thanks.
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Old 07-29-2014, 08:39 PM   #4
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double vapour barrier in Canadian basement wall


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Originally Posted by Buzzman View Post
Yea, I'd like to use spray foam, but I've only opened up a part of the perimeter wall, not the whole thing. To do spray foam properly, I'd have to rip out all of the drywall in the basement, and that's not happening. I guess I'm just going to re-install the fibreglass batts, and vapour barrier the inside (warm side) only. BTW, why do you suggest eliminating the gap behind the insulation? Thanks.
If you have an air gap at the cold concrete, you will get convective loops, lowers the R rating on your insulation(more so in fibrous insulation than foam, think density) The air gap usually gets put in to avoid concrete that may get damp touching material that shouldn't get wet(wood, fibrous insulation) If you can use foam, do it. There is some good info here, just look for posts by Gary in WA and Windows on Wash.
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Old 07-30-2014, 02:09 PM   #5
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double vapour barrier in Canadian basement wall


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If you have an air gap at the cold concrete, you will get convective loops, lowers the R rating on your insulation(more so in fibrous insulation than foam, think density) The air gap usually gets put in to avoid concrete that may get damp touching material that shouldn't get wet(wood, fibrous insulation) If you can use foam, do it. There is some good info here, just look for posts by Gary in WA and Windows on Wash.
No more good information that this right here Canucker.

You don't want that air space in your case.

You could cut and cobble rigid foam in there if you wanted but the air space isn't a benefit in this case.
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