Rockwool Comfortboard 80 as a interior thermal barrier for spray foam
I am looking to insulate the cathedral ceiling of our 3rd floor walk up attic that contains the HVAC for the 2nd and 3rd floor. I am considering doing some form of flash and batt approach, but was looking at options for continuous interior insulation to eliminate thermal bridging.
It looks like 2″ comfortboard 80 is approved as a thermal barrier for up to 4″ of spray foam. Has anyone used this as an interior thermal barrier?
I was generally planning on drywall or blueboard, but this might be a bit easier to put up while getting some additional insulation benefits. Could drywall be later screw directly through the comfortboard or would it be better to put up strapping? I am trying not to loose too much interior space if I later finish this space.
The unvented approach would be R27 3.75″ closed cell foam against the roof deck, R15 rockwool batts, R8 2″ Comforboard 80. This is in 2×10 rafters, so I would be left with 2″ of air space. Is that okay? I could go ahead and vent the roof, but not sure the best way to hand the 3 dormers.
I am located just north of Boston.
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