Shiplap over open cell
I have a cathedral ceiling that I plan on installing primed Pine shiplap planking as my finish.
The roof is constructed of 24″ O.C. 2×4 scissor trusses with 5/8 OSB zip plywood sheathing under asphalt shingles.
The way the trusses are designed I only have about 7 in at the top of the wall and don’t achieve my full 10in depth required for R-39 insulation until about 28″ up the slope.
My insulation contractor installed open cell foam, which does fill the sealed soffit which extends 12″ past the exterior wall.
At the peak the trusses are 20in deep and he only installed 10 to 12 in on average of insulation. I was expecting him to overspray and shave where it wasn’t as deep near the walls.
So I am left with A continuous a space between the insulation and the pine boards I will be installing.
My main question is vapor barrier or not. I was thinking CertainTeed membrain but any advice would be greatly appreciated.
I believe I am in zone 5 20 miles south of Boston Massachusetts
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