Jeff Frantz
4/11/2011
I recently received a quote to install 3" polyiso foam, lay ice and water shield over the entire roof and then install the Berridge 24 gauge galvalume Kynar 500 standing seam metal roof. My concern is attaching the metal to the roof without any decking directly below the metal. Can it be installed this way fastening through 3" of foam?
Info @windowsonwashington.net
An informed customer is our best customer.
4/13/2011
Yes it can. Your installer needs to take special care to not overdrive the fasteners at all and cause deflection in the roof. In this type of installation, it would be nice to install the roof on a system of purlins/battens to create some over-deck venting. Depending on the construction of the home, I would like to see the seams on the rigid board taped for air tightness and controlling the migration of warm/moist air. What is the current construction of the home (i.e. framing type, attic, etc) that necessitates the foam layer?
Jeff Frantz
4/15/2011
The house has T&G ceiling with exposed rafters. The current insulation is approximately 1" of expanded foam with asphalt shingles. They proposed to remove the shingles and add the 3" polyiso directly over the 1" foam and plywood with no vent space...they said it really wasn't needed. I would really like to have a vented space under the roof since it would more than likely cut down on the AC in the summer. I'm sure it would also help any ice damming.
Info @windowsonwashington.net
An informed customer is our best customer.
4/15/2011
Pull up the 1" foam carefully if you can and save it. Bring the roof right down to the T&G structure. Put down Ice and Water over the entire roof and make sure that it is sealed good and tight to the T&G roof. This will air seal the roof and prevent any air loss and eliminate most of the moisture movement and air movement. Now, apply your 3" foam and 1" foam if you can re-use it. Putting the roof on purlins and providing some over deck venting is a great idea as well. Here is a link to and article detailing a cold roof design. Not a cheap approach but certainly well thought out. It is a down-loadable pdf. http://danperkinsroof.com/1108_JCL_Perkins_A.pdf
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