Interior air barrier in walls
Thanks to help from those here last year I have built a holiday home cabin/garage close to Vancouver, Canada, (Zone 4C I recall). The exterior is complete and my project this summer is to complete the interior.
Firstly, this ‘outbuilding’ is not considered by the inspector to be a habitable building, so many ‘code’ rules don’t apply. I believe this means we do not need to install an interior vapour barrier as per the norm in the area. Moreover, my reading on here suggests I should not need an interior vapour barrier anyway. I’m I correct in this assumption?
So that moves me to the need for an interior air barrier, specifically on the walls.
We’ve already purchased Fiberglass Batts for the wall cavities, although not ideal, due to a mix up with the main contractor its what we have.
I know Martin has said double air barriers aren’t really needed, but: “To a large extent, double air barriers are an attempt to respond to the inherent performance problems of fiberglass batts.” So don’t use fiberglass batts.”
I DIY air tested with a large extractor fan installed in a window and the building seems pretty tight having used can foam to seal a few leaks I found with a smoke tester.
I know the local drywall guys won’t be able to do an “airtight” drywall approach. But does it matter? Given my exterior air barrier appears tight, do I just drywall like normal and be done with it?
Or do I need to think about installing something like CertainTeed Membrain under the drywall where I can be careful about interior air sealing to base and top plates and openings? It seams fairly expensive and frankly would prefer not to unless necessary.
Also, this is a cabin, it won’t ever be occupied full time, but I do want to build it right.
Two storey 800 sq ft garage ground floor. Living area, 2 bedrooms and bath above. 1:12 shed roof.
Wall build up: 2×6 studs, Zip system sheathing taped, 2″ rockwool comfortboard, strapping, Cedar/Corrugated metal siding.
Ceiling building up: T&G truck decking over 4X10 douglas fir beams, modified bitumen vapor barrier (I think it was SOPRAVAP’R), 2 x 4″ layers polyiso, 2 x 4 battons/strapping, 1/2″ ply, EPDM membrane. Unvented hot roof essentially.
Floor build up: OSB subfloor, fiberglass batts 12″, 1″ Silverboard foil-faced EPS (airsealed as much as possible). This is the ‘ceiling’ of the garage underneath.
GBA Detail Library
A collection of one thousand construction details organized by climate and house part