Why Isn’t Your Roof White Already?

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Studies are showing that most—but not all–Americans should be following U.S. Secretary of Energy Steve Chu’s recommendation that people paint their roofs white. On hot days, it’s 20 percent or more cheaper to air-condition a house with a white roof rather than a traditional charcoal-colored asphalt roof. It’s another simple solution for saving money.

If you’re consuming less energy, it obviously saves you some cash, and it also cuts back on carbon dioxide emissions. The Times explains the science:

The physics behind cool roofs is simple. Solar energy delivers both light and heat, and the heat from sunlight is readily absorbed by dark colors. (An asphalt roof in New York can rise to 180 degrees on a hot summer day.) Lighter colors, however, reflect back a sizable fraction of the radiation, helping to keep a building — and, more broadly, the city and Earth — cooler. They also re-emit some of the heat they absorb.

But a white roof might not be for everyone. A dark roof is exactly what you want in northerly locales in the winter, when you’re trying to attract the heat and lessen the cost of heating your home:

Some roofing specialists and architects argue that supporters fail to account for climate differences or the complexities of roof construction. In cooler climates, they say, reflective roofs can mean higher heating bills.

Scientists acknowledge that the extra heating costs may outweigh the air-conditioning savings in cities like Detroit or Minneapolis.
But for most types of construction, they say, light roofs yield significant net benefits as far north as New York or Chicago.

Although those cities have cold winters, they are heat islands in the summer, with hundreds of thousands of square feet of roof surface absorbing energy.