Unvented cathedral ceiling with interior rigid foam
I have a Cape cod style house. The upstairs is completely gutted and will be finished as unvented cathederal ceilings. The roof rafters are 2x6s with some 2x8s on a big dormer. I was planning to open cell foam all cavities and add 2 layers of rigid foam under the rafters with offset taped seams. ( 4″ total under 2x6s and 2″ total under 2x8s) Spray foaming any gaps. Then use furring strips and drywall. Does this seem ok? Would untrimmed closed cell foam be better? But it would leave air pockets.
I was planning the same thing for the 2×4 walls with 1″ of interior rigid foam.
GBA Detail Library
A collection of one thousand construction details organized by climate and house part