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Can a metal roof be installed over existing asphalt shingle roof?
Todd Miller
Isaiah Industries, Inc.
In many cases, yes. Every job must be evaluated on its own basis in light of the new product being installed, the exact condition of the existing roof, and local building codes. For example, existing roof deformation, leaks, or weight issues must be addressed. However, the low weight of metal roofing and the design of many products encourages their installation over the old shingles. Leaving the old shingles in place accomplishes three things: 1) It allows the property owner to spend their money on a better roof rather than on removing and disposing of the old roof. 2) It increases the thermal mass of the home, for increased energy efficiency. 3) It prevents the need to dispose of old shingles in a landfill. I have worked with residential metal roofing for over 30 years and most of the installations I have worked with have been over the old shingles. Out of thousands of jobs, I have yet to later go back on a job and say that perhaps the old shingles should have been removed after all. In most cases, the metal roof is adding no more additional weight than what the last layer of shingles has lost over the years with granules washing away and oils evaporating.
Eric Novotny
An informed customer is the Best Customer!
Yes. They can be installed over asphalt with a proper isolation layer between the asphalt and the new metal roof. Being in Florida where you have a largely dominant cooling season, it would be best to have some sort of airspace between the metal and the asphalt to avoid the thermal energy transfer and resultant storage as well as some over deck convective cooling.

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