Permeability of retrofit insulation in zone 4C
How important is maintaining vapor permeability in a cool humid climate in the case of an insulation retrofit that neither replaces the interior or exterior finish, but merely adds insulation? We’ll presume hypothetically equivalent sealing and leak prevention, and equivalent r values. If most moisture comes in through leaks, how much difference will it make to an old zone 4C home whether the in-fill is semi-impermeable, semi-permeable, or quite permeable?
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