Interior air/vapour barrier alternatives
My question concerns the application/installation of an air barrier on a new construction cabin. I’m in climate zone 5 in the dry, southern interior region of BC in Canada. Summers are very hot and dry (often one of the hottest spots in Canada) and winters are cold and usually dry.
The basic structure is already in place. The walls are staggered-stud 2×4 construction (on 2×8 plates). Exterior sheathing is 1/2 plywood. No vapour barrier/house wrap or exterior siding installed yet…just plywood. Insulation is two, staggered layers of R14 Roxul. The roof structure is 2×4 trusses sheathed with 1/2″ plywood, which is covered in roofing paper and metal roofing. Ceiling insulation is two layers of R22 Roxul.
The interior ceiling (pine t&g) is already in place with 6 mil poly underneath. I’m now beginning the process of finishing the interior walls and have only just now discovered that 6 mil poly may not be the best option for the walls (too late to change the ceiling!).
I was not planning on using drywall on the interior walls. I’m leaning towards 1/2″ or 5/8″ plywood (not OSB) for the finished walls, which I would either paint or wallpaper over.
So, it seems that poly is being deemed unnecessary or overkill for most climate zones. Can I simply nail up plywood to the interior studs (without poly underneath), seal the seams somehow and then paint with a vapour retardant primer/paint? My plan for the exterior is to use 15# paper over the plywood followed by corrugated metal roofing oriented vertically (no stand-off). Options or suggestions welcome.
By the way, building inspectors/codes are not a concern in this situation. The only concern is good practice.
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