Options if inspector insists on interior poly barrier?
I’m planning a small one-room addition on my home in Ottawa, Canada (zone 5-6 based on my read of the US map). This will have a simple shed-style roof with a cathedral ceiling and vertical board siding.
Having followed GBA for a while I would like to use the suggested wall assembly of exterior foam (sufficient for warm sheathing), batt or blown insulation in the stud cavities, and airtight drywall — and no interior poly barrier.
I have been warned by my designer that the building department here is not likely to approve anything that does not include the poly “VB”. If that’s truly the case, what are the options for a better-than-average insulation system? (“average” around here being stud cavity insulation only, thermal bridging be damned)
If I must have the interior poly, is it safe to have any amount of exterior foam on the walls or roof? I know some foams are vapor-permeable, but if I have say 1″ or 2″ of exterior XPS foam, is that really a wall assembly that can dry to the outside? My instincts say “no” but if I’m wrong please let me know!
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