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
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Replies
In short some manufacturers won't waranty it - but most do & based off all the recent studies I have seen say that it may cause the shingles to lose 2 weeks off their actual lifetime
I have done a few & have had no issues, nor seen any degradation
http://blog.sls-construction.com/2011/what-is-a-hot-roof
Will,
CertainTeed offers a reduced warranty of 10 years when their shingles are used on unvented roofs:
http://www.certainteed.com/resources/GeneralAsphaltShinglesWarrantyEnglish.pdf
Frankly, asphalt shingle warranties from ALL companies contain so many limitations and exclusions (for example, labor exclusions) that roofing warranties aren't worth much. If you ever need a warranty, you're never going to get much from any manufacturer.
Thanks for the answers. Great article, Sean; thanks for the link. Martin, that sure is one long warranty! But at least I feel better proceeding with the unvented "hot" roofs I've been working on. My current design calls for red shingles ( http://www.travisprange.com/blog/images/maine.lighthouse.jpg (Color, not design!!...) ); any thoughts on whether or not a lighter (or darker) color would significantly impact the shingles' longevity?...
Thanks, Will
Will,
Lighter shingles stay cooler and probably last a few years longer than darker shingles.
But lighter shingles really show the algae. I see a lot of light-colored shingle roofs that are ugly with algae stains after only 4 or 5 years. If you include a galvanized ridge cap, exposed to the weather, the zinc in the ridge cap will leach slowly down the roof and control algae growth.
Will, I've heard this question many times. My question back is- do you know anyone that has actually cashed in a warranty on asphalt shingles? I don't, they are probably out there, but rare. You may buy 30 year shingles, but chances are good they'll be replaced before then anyway (storm damage, aesthetically worn out, etc.). If a defect showed up in the first year or so maybe, but when you get 10, 15, years out, as Martin said you're not going to have much luck. In my opinion, the other benefits of the assembly outweigh a decreased shingle "warranty".