Closed cell foam insulation


Old 09-16-10, 06:55 AM
Thread Starter
Join Date: Dec 2009
Location: VA
Posts: 35
Closed cell foam insulation

Need some advice/input on having closed cell foam insulation sprayed on the underside of the roof decking in my attic. They say two to 2 1/2 inches makes a considerable diffrence in overall attic temps. I have seen/read info on pros and cons of doing it. My concern is will it effect the shingle warranty. Will it cause ice dams to form easier or will it make them harder to form. Will it prevent the heat ransfer into the attic. Will it lower the actual attic temp? Is it worth the investment or are the other ways to get the same results that would costs the same or less?

Thanks for your time

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Old 09-17-10, 06:09 AM
Join Date: Aug 2009
Location: USA
Posts: 4,941
There are some arguments against having an unvented roof assembly. One of those is the voiding of the shingle warranty. It all depends on the manufacturer. According to what I have heard, it will raise the shingle temperature around 5-7 degrees compared to a vented roof.

It should make ice dams harder to form because it will keep the roof colder. What you are getting will be around R-19. You can add an unfaced batt over the spray foam to increase the R value for less money. Based on the spray manufacturer I contacted, they recommended that you should have at least 50% of the total R value in foam. So if you have R-19 of foam, don't add more than R-19 in batts over it.

It will reduce heat transfer into the attic. The attic then becomes part of the conditioned space of the home. If you have HVAC ductwork in the attic, it will make the most difference to do this.
Old 09-24-10, 01:24 PM
Join Date: Sep 2006
Location: USA
Posts: 4
What about the possibility of moisture build up between the shingles and the spray foam. In case of a leak, couldn't it go undetected for a time and cause more deck damage and rot than without the foam??

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