Vapour Retarder Required in Basement?
Rikcor
| Posted in General Questions on
Hello,
I am renovating our basement in our 1950’s bungalow in Edmonton Alberta. I am planning to insulate the interior side of the foundation wall with R10 Halo Interra rigid foam insulation. Then I will frame a 2×4 wall and insulate with R12 fiberglass insulation. Will I require vapour retarder membrane on the interior side of the 2×4 wall? Or, will the Halo be sufficient to protect from the dew point reaching the interior of the 2×4 wall thus making a vapour retarder membrane unnecessary?
Any advice and recommendations would be appreciated.
Thank you.
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Replies
Rikcor,
You've got it right: the rigid insulation is sufficiently thick to keep condensation for occurring on it's inside face. No other vapour-retarder is necessary.
https://www.greenbuildingadvisor.com/article/three-ways-to-insulate-a-basement-wall
Great thanks!
That's what I thought. I just hope the inspector understands. Seem like there's a lot of them still misinformed. The building code states that vapor barrier is required on the warm side so they seem to assume that means on the outside of the wall assembly no matter what.
Rikcor,
If they are resistant, directing them to 9.25.4.3 will hopefully help.
"3) Where the same product is used for the vapour barrier and the insulation, the product shall be installed sufficiently close to the warm side of the assembly to prevent condensation at design conditions."
(See Notes A-9.25.4.3.(2), A-9.25.5.1.(1) and A-9.25.5.2.)
I'd go further to say that not only is a vapor-retarder not necessary, it's not a good idea. That fiberglass would be stuck between two vapor blocks, it needs to be able to dry to one side or the other. To the extent it's going to be able to dry it's going to be to the interior.
DC,
Yes, that's a better way of putting it.
You are on the right track. I presume you are finishing your basement with drywall, however if not, one thing to keep in mind is that R12 fibreglass batts may not satisfy your inspector as a thermal barrier to protect the foam. I’m in Ontario and our building departments generally require R22 Rockwool batts or 2” Rockwool comfortboard if drywall is not being installed.