TOPIC: Energy Efficiency
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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?
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.
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