For an unvented cathedral ceiling is a roofing deck sandwich of 1/2" plywood and 2" of both sides foil faced polyiso, OK ?
I am planning the building of a new year round ENERGY STAR VERSION 3 lakefront home on Andover Lake, CT. The home will have an unvented cathedral ceiling with the following insulation and sheathing configuration. I refuse to use OSB or SIPS in the construction of my home due to their inferior water resistance and durability, (NOTE: California does not approve SIPS in residential construction in many areas.) The insulation/sheathing configuration are the following::
The 2 x 10 rafters 16"OC will be filled with 3" closed cell spray polyurethane foam against the underside of the roof sheathing. The remainder of the rafter cavity will be filled with R19 FG batts. The roof sheathing of this unvented cathedral ceiling/roof will be a sandwich configuration consisting of 1/2 " plywood, 2" of both sides foil faced polyiso, 1/2 ' plywood, synthetic underlayment, and 30 year architectural asphalt shingles. Polyiso was choosen because of its greater stability at higher temps compared to XPS. Do you see any problems with this insulation/sheathing configuration? Will the foil face on both sides of the 2" polyiso trap moisture in the lower plywood sheathing layer between the foil face and the impermeable closed cell spray foam below causing rot of this plywood layer?
I will also be using vinyl siding with 3/4 " foil faced both sides polyiso over 1/2" plywood sheathing with 2" closed cell spray foam and R13 FG batts betwen the 2 x 6 wall joists. Do you see any problems with this configuration? The home wiil be heated by a ground source heat pump,closed vertical loop well with air ductwork and an ERV energy recovery ventilation system.
I am particulary interested in your recommendations for the specifications on the plywood sheathing, i.e. ply, waterproof glue, CDX,, thickness, etc for both the walls and roof. I am also concerned with the use of duplicate foil faced polyiso, such as Dow Tuff R and the possible trapping of rotting moisture in the configurations above? Thank You.
Posted May 31, 2012 11:42 AM ET
Edited May 31, 2012 12:03 PM ET
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