Insulating underside of attic roof-line


Old 05-18-09, 01:10 PM
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Insulating underside of attic roof-line

Is it ok to use open-cell spray foam insulation on the underside of the roof? I am used to batts with a baffle vent - can the foam be directly applied to the sheathing? Just in case, I can pay a little extra and have it applied over baffle vents as well. I have a brand new $$$ roof and would hate to do anything that jeopardizes the lifetime of the sheathing and then the roof..
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Old 05-18-09, 02:33 PM
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The debate between a "hot roof" and a "cold roof" is still going on. Some of the hot roof issues, that's filling it with foam, are shingle warrenty, and how would you know if you have a leak.

Some contractors have produced letters from shingle mfgs stating no problem with the warrenty, but I haven't seen any claim results where they had shingle problems with a hot roof and all was taken care of.

As for leaks, they are going to happen. Not only will the damage go un-noticed for longer, thus perhaps be worse, but how do you fix it.

Actually fixing or doing anything wall or ceiling cavity that are filled with foam is always going to be an issue. How many homes do you see being totally remodeled 20 plus years after they were built. What will sprayed in foam do to the remodel costs. I don't know, but I doubt it will make them less expensive, and that would essentially lower the value of the home. Pure speculation, and that is the primary problem with doing something different, you just don't know what 40 years in the field will do.

Old 05-18-09, 05:17 PM
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I will say that you don't won't to use open cell. Closed cell is far superior in every way. From what I understand and have read closed cell spray foam will only increase the shingle temp from 3 to 5 degrees. But I would check with the shingle rep and get it in writing.
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