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Ice damming

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Guest User
5/12/2008
We built two schools in Vernal Utah. Roof is composed of standing-seam metal roof over underlayment, 2" poly-iso insulation and 1 1/2" metal b-deck. Under the decking we installed r-30 batt insulation. The past winter we saw severe water leaks coming out of winter. Solution? If we dropped the batt insulation to the bottom of the steel bar joists, would this supply ventilation consistent with a cold roof and prevent the ice damming? To attach the metal roof requires screws which penetrate the ice/water shield underlayment. Doesn't this void the purpose of the underlayment? This seems to be a problem that the metal roofing and underlayment industries need to address.
Ken Buchinger
NCI Building Systems, Inc.
5/13/2008
Moving the batt insulation as you suggest, would effectively be wasting the rigid insulation under the metal roof and probably wouldn't solve the problem by itself. To properly ventilate the cavity, you would need air intake at the soffit and a vented ridge. You may want to explore heat cables in the concealed gutter and at the eave. Peel and stick membranes are supposed to be self sealing around screws and nails. This feature doesn't work as well when applying it over poly iso. In the future, I would consider using nail base insulation to allow the peel and stick membrane to provide a better seal.
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