Vapor Control for Newly Insulated Exterior Walls
Hi all – As part of a DIY remodel I am retrofitting some of the exterior walls of my 1955 house in Zone 4C (Seattle) that have never had insulation before. From the inside working outward:
– The framing is 2x4s, 16″ on center
– The sheathing is horizontal 1×12 boards with gaps between them from 1/8″ to 1/4″. Not shiplap, not t&g. Photo attached.
– The housewwrap appears to be some kind of beige paper. Is this “kraft” paper? Photo attached.
– The siding is vertical cedar channel lap, about 1×12
I am working from the interior. When I am done with the insulation (and whatever else GBA advises for vapor control!) I am going to finish the walls with 5/8″ drywall, painted with latex paint.
The simplest thing for me to do – and all I’m hoping to do – is to add some Rockwool ComfortBatts and call it a day. R15 batts with a 25% framing factor equals R9 for the cavity and framing, which isn’t great, but I don’t have the square footage to lose to do bonifiglio strips, nor do I have the money for CCSF or anything with a much higher R per inch. Plus, R9 is a heck of a lot better than no insulation.
Will that work from a vapor perspective?
Do I need to address the gaps between the sheathing boards, with tape, caulk, or canned spray foam? Do I need a smart vapor retarder?
I’m not that all that interested in making the house a blower-door test all-star, as I already spend <$500/year to heat the place, and I don’t have the means to get any balanced mechanical ventilation, so if I tighten the walls up I will just need to run the bathroom exhaust fans more to keep CO2 down for my family of 6. But I am willing to do a bit more work than just packing some batts in – and potentially spend a few more dollars – IF that work is necessary to keep the sheathing from getting too wet!
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