I'm assuming that you are installing the spray polyurethane foam to the underside of the roof deck. The concern here is with an
unvented attic where insulation is installed directly under the roof deck, the shingles may degrade rapidly due to the increased
heat caused by the insulation. This concern is over exaggerated. There are a couple excellent papers and presentations written by
Building Science Corporation (www.buildingscience.com) that cover their research regarding shingle life in unvented attics. They
conclude that in Las Vegas, one of the hottest locations in the US, the average roof deck temperature difference between a unvented
attic and a vented attic is 17 F. This is from research that they conducted on actual homes. This difference would only be less in
the rest of the country. They have also determined that asphalt shingles installed over VENTED roof decks in hot-dry climates are
generally warmer than the same shingles installed over UNVENTED shingles in a hot-humid climate like Orlando. Finally, the
difference in color from white and to black creates a larger temperature difference than unvented versus vented roof decks. The
argument for these points is that shingle manufacturers do not have separate warranties for different climate zones or different
shingle colors. The small increase in shingle temperature due to vented versus unvented is insignificant compared to other factors.
Feel free to click on the "Contact the FAQ Administrator" link to ask me a follow-up question.
Jason M. Hoerter, P.E.
Sr. Product Manager
Copyright © 2012 NCFI Polyurethanes