Energy 101: Cool Roofs
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MR. : Maybe you’ve never given much thought about what color your roof is or what it’s made of, but your roof could be costing you more money than you know to cool your home or office building, especially if you live in a warmer climate.
Think about it this way: In the summertime, we wear light-colored clothes because they keep us cooler. Lighter clothes reflect rather than absorb the heat of the sun. It’s the same with your roof. A cool roof is often light in color and made of materials that have what’s called high solar reflectance. That means it’s able to reflect a lot of the sun’s light that a conventional roof would absorb, heating up the building.
You see, when the weather is warm, a conventional roof is the hottest place in the building. It can be well over 50 degrees hotter than the temperature outside. So if you don’t have air conditioning, a lot of that discomfort you feel may be coming from the roof. If a building with a standard darker roof is air conditioned, the cost for comfort is much higher in order to counteract all that heat pouring in from above.
Insulation slows the transfer of heat inside but doesn’t eliminate it. Researchers have measured energy savings up to 10 to 15 percent for homes with cool roof coatings. And if a standard dark roof reaches 150 degrees or more, a cool roof can actually reduce the roof temperature a lot. A cool roof may only be five or 10 degrees warmer than the temperature outside on a hot sunny day.
All right. So here’s a big plus for the environment. A cool roof helps mitigate a phenomenon known as the “urban heat island.” The temperature in developed urban areas tends to be two to five degrees warmer than surrounding areas. That’s because ground covered by pavement and dark buildings absorbs more heat. So the heat stays in the atmosphere longer.
A variation of the cool roof is the green roof, sometimes called a living roof. That’s because flowers and plants and even a vegetable garden grow in a special soil system right on top of the building. Cool roofs aren’t super high-tech, and that’s part of their appeal. They’re a relatively simple and effective way to improve our environment and lower energy costs.