Rockwool in Cathedral Ceiling
Wife and I purchased a 1948 house in Oregon (zone 5)
Had a finished upstairs when purchased. We have basically ripped every exterior wall apart as it had no insulation and have re-wired the whole house, and are now at the insulating stages. Exterior walls are 2×4, with a horizontal layer of 3/4 t&g fir, vapor barrier and then Hardie board.
Our plan was to use r15 rockwool (have purchased already) in the exterior walls and 1/2 rock on top. No vapor barrier between the two.
For cathedral ceiling upstairs there is a cavity at the peak of the roof for wires/lights etc. there is a ridge vent installed the length of the roof. And about every 5 bays a roof vent is installed on the east facing side of roof. Being a 2×4 rafters we were going to use the rockwool r15 with no barrier and 1/2 rock. I know the r-value is not great, but anything is better than what was there before. Also thought about using 1″ foam atop the studs and screwing drywall through that to help with thermal bridging/increasing r-value. Just would suck more the ceiling height doing so.
My concern is the rockwool batts when installed in the stud bays, has very little to no air gap behind the batt. What would you guys recommend? I have looked into using a rafter vent in each bay but see potential issues compressing the rockwool ontop the vents. Also it’s a lot of bays.
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