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was: attic fans

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I would have to research this a bit, but if you insulate a roof deck and in between trusses in a normal attic space situation, this is no different then insulating the VERY popular cathedral and vaulted ceilings where there is only 3.5" space between the gyp and sheathing that is insulated. I don't know and have not seen any particular problems with these roofs regarding shingle degradation.
 
In the case where the underside of the sheathing is sprayed with foam, the attic is then cooled via ducts, so you have a cool surface under your insulation (and the air is dry). My thoughts are that this is better then a 130 deg attic, and is no different then a wall system. I would have to research the shingle warranty angle, I do a lot of forensic work involving shingles and have not run across that. The other fear would be that if moisture makes it through the sheathing or around it at the joints, the foam would lock it in. But as I understand it these foams have varying degrees of permeability. The contractor I know using this system and the installers of the product claim an improved roof life due to the decreased temp below the roof surface.
 
Andrew
 
 
From: Roger Davis <sds_rdavis(--nospam--at)yahoo.com>
Subject: Re: attic fans

That is true and roof shingle warranties are often void in such installations.

Jim Getaz <
jgetaz(--nospam--at)shockeyprecast.com> wrote:        st1\:*{behavior:url(#default#ieooui) }                            Andrew,
                          If the roof is insulated between the trusses in Florida, what happens to the roof material itself and the sheathing. It seems to me they'd get hot and deteriorate more quickly than if they were ventilated.
              Thank you,
              Jim Getaz