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TOPIC: Energy Efficiency

Heat gain/retention in asphalt shingles under Stone coated steel, radiant barrier?

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I am considering a Tek industries Hurricane shake stone coated steel roof over my asphalt roof. This will be installed on battens and include a foam layer. They are advertised to reflect 90% of the radiant heat from the sun. It is my understanding, however, that asphalt shingles tend to absorb and retain heat. Even though there is an air gap, I would like to optimize my radiant heat reflection. I live in Texas, and the attic gets hot! A cooler attic would increase my storage space.

Do you think adding radiant barrier (95-97% reflection of radiant heat) over the asphalt shingles would be beneficial to limit the heat gain/retention of the asphalt? Is it possible to calculate the how much this would decrease the temperature in the attic vs the 90% reflection inherent to the metal roof?

Thanks

Patrick Frey

8/19/2020
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Whereas many painted metal products have special heat reflective pigments in the coatings, that typically is not the case with most stone-coated products. Therefore, the actual reflectivity of most stone-coated products comes from color usually -- light colors being more reflective. However, the energy efficiency of stone-coated products comes a great deal from the integral airspace that separates the metal from the roof deck, blocking conductive heat transfer. Adding a radiant barrier on top of the roof deck or even in the attic can indeed be helpful and is sometimes done with stone-coated products. I do not have any empirical test data though. TEK is not a member of the Metal Roofing Alliance but they may have data of their own. Making sure the attic has proper ventilation is also usually very helpful.

Todd Miller
Todd Miller
Isaiah Industries, Inc.

8/19/2020
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