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Cool Roofs for Hot Climates

Cool Roofs for Hot Climates

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    Florida Solar Energy Center researchers compared the air-conditioning power use of seven identically built houses with different roof coverings. Reflective roofing dramatically reduced total power use (bottom chart) and had an even greater effect on peak A/C power demand (middle chart). Insulating the roof deck and sealing the attic, without using a reflective roof, cut total energy use somewhat but did not reduce peak cooling loads noticeably.

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    Kynar roof coatings using spectrally selective pigments from Ferro Corporation allow Classic Roofs to produce aluminum and steel shingles in several dark colors that meet Energy Star minimums with solar reflectances better than white asphalt shingles.

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    Tests indicate that the colors will sharply reduce solar heat gain through the roof.

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    Unfinished galvanized steel roofs may look shiny when new, but they age quickly to become very nonreflective. The infrared thermal scan shows the drop ceiling at a radiant temperature of almost 90°F under the metal roof of a strip mall building, despite insulation below the roofing.

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    When FSEC researchers applied a reflective coating, the building's air-conditioning power use dropped 16%, and tenants reported improved comfort. One tenant even called to thank the landlord for fixing the air conditioner. (He hadn’t.)

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    Radiant barrier foil under the rafters stops heat from radiating into the attic, because the foil will not emit heat radiation even when it's hot.

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    FI-Foil Corp.

    Rafters after applicaiton of radiant barrier foil.

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    Solec Inc.

    Lo/Mit lowemissivity silicone coating spray-applied to the roof underside is a cost-effective alternative method.


Options for Stopping Rooftop Heat Gain

  • Options for Stopping Rooftop Heat Gain
    Options for Stopping Rooftop Heat Gain

Field research at the Florida Solar Energy Center (FSEC) has found several effective ways to limit rooftop heat gain in sunny conditions. Using a highly reflective roofing material is the simplest and most effective: It stops the sun's energy before any heat is absorbed, so that even the roof sheathing and framing stay cool. If the existing roof is dark colored or the customer prefers a darker roof, heat can still be blocked by adding a radiant barrier foil just below the roof deck. Savings from this method are roughly comparable to the saving achieved with reflective roofing; however, some conductive heating of the attic space will still take place, and the roof deck and shingles will experience some increased heat stress. A third option is to increase the insulation between the attic and the living space below, and to run the hvac ductwork within the conditioned space rather than in the unconditioned attic. This method has a smaller effect on cooling loads than the reflective or radiant barrier roof systems but is effective at reducing heating loads as well as cooling loads, making it the most cost-effective option in mixed heating and cooling climates.