10 Jun '11, 8pm

Green Building Q&A: flash and batt insulation at roof

William, Be sure to discuss this issue with your local code official before proceeding. The interpretation of your local code official determines how you can proceed. The code requirements found in section R806.4 of the 2009 IRC are summarized in my article, Calculating the Minimum Thickness of Rigid Foam Sheathing . That code section requires that a certain amount (R-20 in your case) of air-impermeable insulation be “applied in direct contact with the underside of the structural roof sheathing.” The code does not include credit for insulation installed above the roof sheathing. This code provision is illogical. In a situation like yours, with some rigid foam above the sheathing and some closed-cell spray foam below, both types of foam work together to reduce the condensation risk. However, why are you going this route? It would be a lot simpler just to put as much rigid f...

Full article: http://www.greenbuildingadvisor.com/community/forum/energ...

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buildinggreen.com 09 Jun '11, 2pm

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greenroofs.com 13 Jun '11, 1pm

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