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TOPIC: General Discussion

Metal roof over asphalt shingles

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I am considering putting a galvalume metal roof on my double wide. The pitch is sufficient and I plan on this being a DIY project. I was wondering what would give me the best energy savings, putting the roof on with an "air gap" or laying insulation panels down? If I do the air gap how do I need to lay out the 1x's?
Tom Pepera

1/13/2011
Certainly an air gap is one component. To get real benefit from it, you need to have air intake at the eave and exhaust at the ridge. Above sheathing ventilation has been proven to significantly reduce the heat flow into a building. You can put a radiant barrier sheet down before you install the 1x's to reflect out more heat. You could also add a layer of rigid insulation before the 1x's as well. To get the air flow, you would use a batten/counterbatten system, where short 1x's are spaced out from eave to ridge down the length of the house. Then continuous 1x's are installed to the shorter ones to provide an air space. The spacing of the 1x's is dependant upon the panel used. I would consult with the manufacturer about spacing required for the panel you use. Also, make sure the 1x's are fastened well to the existing structure.
Ken Buchinger
NCI Building Systems, Inc.

1/14/2011
Definitely a full length air gap and a radiant barrier as Ken recommends. Insulation is an option but I would place in 3rd in that list of 3. If it is not too difficult, removal of that asphalt roof would not hurt either. Asphalt will hang on to that heat for much longer than the plywood substructure will. Eric Novotny
Eric Novotny
An informed customer is the Best Customer!

1/14/2011