Vapor retarder vs Airtight Drywall…or both? …or neither?
Remodeling a couple rooms of a 1947 cottage in climate zone4 (Seattle). From outside to in it is currently horizontal cedar siding, tar paper, board sheathing, 2×4, plaster and lath. No insulation in the walls (though the crawl and attic are insulated). The plaster and lath is already down and I’m installing rockwool insulation.
The question is what type of vapor retarder for the interior? I know that poly is a no-no, so looking at Membrain but wondering how necessary it is. Would an airtight drywall approach make the Membrain redundant? Would Membrain be better than bothering with airtight drywall? Is a vapor retarder even needed in zone 4? Is Rockwool ok without a vapor retarder? Is the fact that it’s board sheathing on the outside wall make all this pointless? Aaaaaaaagh!!!!
Too many variables and too little definitive information have left me second guessing everything.
Thanks in advance for any help,
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