Photo: NY Times
Although the idea has been around for a while, white roofs are now 'cool'. Well, I suppose they've always been that way, its just that with climate change heating things up, and more and more people looking to cut energy costs, now its getting talked about. You may have seen them on the tops of malls and office buildings, but now white roofs are moving into residential areas. In the same way that a white t-shirt is going to keep you cooler than a black one on a sunny day, a roof that is white in color will keep your home or office cooler than a dark-shingled or tar roof. All that sunlight beating down gets reflected off of a white roof, creating an energy-efficient way to chill out. According to the NY Times, a white roof can cut 20 percent of air conditioning costs on a sunny day. This means less energy use, fewer carbon dioxide emissions, and more money in your pocket.
However, the idea also works in reverse. In winter, a white roof is still going to be reflecting sunlight away, potentially increasing heating demands. A black roof absorbs the sun's rays, which helps to keep the house warm in winter. If you live somewhere where there is more winter than summer, additional heating costs in winter may outweigh savings on air conditioning from a white roof in the summer.
Check out this article from the NY Times for more on white roofs:
http://www.nytimes.com/2009/07/30/science/earth/30degrees.html?_r=1
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