Asphalt shingles and unvented roof construction
For complex roof forms (dormers, valleys, etc.) that enclose living space (resulting in sloped ceilings & knee walls) I’m a big fan of unvented (“hot”) roof construction, primarily because it seems difficult, if not impossible, to effectively maintain continuous, balanced ventilation from eaves to high points with such roofs. Also, there’s a certain simplicity to keeping the building envelope out at the roof, with its advantages of keeping ducts and access panels all within conditioned space, and with its potentially simpler construction.
But, what about asphalt shingles on such unvented roofs?? Lighter shingles are better than darker shingles. I’ve read that a 3/4″ vent space doesn’t dissipate heat fast enough to really make much of a difference. My understanding is that shingle manufacturer’s won’t warranty their shingles in such applications (except for Elk which did, but I guess no longer does). Most recently, a SIPs manufacturer has recommended 3/4″ strapping with an additional layer of OSB under asphalt shingles.
Aside from adding a whole layer of sheathing, not to mention lots of strapping, this recommendation to vent asphalt shingles over SIPs defeats the whole purpose of not doing vented construction in the first place.
What is the latest thinking on this subject?
Thanks! -Will Tinkelenberg