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White Roofs Can Save 15% on Energy Costs

U.S. Department of Energy Secretary Steven Chu today announced a series of initiatives underway at the Department of Energy to more broadly implement cool roof technologies on DOE facilities and buildings across the federal government. Cool roofs use lighter-colored roofing surfaces or special coatings to reflect more of the sun’s heat, helping improve building efficiency by reducing cooling costs and offsetting carbon emissions.

Under the Executive Order on Sustainability, the federal government has committed to reducing its greenhouse gas emissions 28 percent by 2020. As part of that effort, Secretary Chu has directed all DOE offices to install cool roofs, whenever cost effective over the lifetime of the roof, when constructing new roofs or replacing old ones at DOE facilities. With cool roofs, these federal buildings will consume less energy, offset additional carbon emissions, and save money. The memorandum from Secretary Chu is available HERE.

Roofs and road pavement cover 50 to 65 percent of urban areas. Because they absorb so much heat, dark-colored roofs and roadways create what is called the “urban heat island effect,” where a city is significantly warmer than its surrounding rural areas.  Cool roofs significantly reduce the heat island effect and improve air quality by reducing emissions. A recent study by researchers at Lawrence Berkeley National Laboratory (LBNL) found that using cool roofs and cool pavements in cities around the world can help reduce the demand for air conditioning, cool entire cities, and potentially cancel the heating effect of up to two years of worldwide carbon dioxide emissions. More information on the LBNL study is available HERE.

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3 thoughts on “White Roofs Can Save 15% on Energy Costs

  1. White roofs may help to reduce the heat inside the buildings and less energy will be needed to cool it. But light coloured roofs will reflect heat back into the atmosphere contributong to atmospheric/global warming?

  2. No – the light and heat reflected from the roofs will not contribute more to global warming.

    The greenhouse effect refers to long-wavelength infra-red radiation being converted to random atmospheric heat energy via CO2 absorption that is coupled with other mechanisms. But the reflected energy will contain essentially the same wavelengths as the incoming solar energy did, with very little additional infra-red components. The atmosphere is more transparent at those wavelengths, allowing the energy to pass right back out. (This is a simplified description)

    Furthermore, a black roof will heat up tremendously. The resulting hot roof will radiate strongly at infra-red wavelengths. That radiated energy will certianly contribute to the greenhouse effect.

  3. And finally, a hot black roof also radiates and conducts heat into the building interior. A person living or working underneath a hot black roof will crank up the air conditioning in the cooling season even more, to compensate. The nearby fossil-fuel-burning power plant will release yet more CO2 into the atmosphere as it supplies the extra electricity.

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