Tuesday, April 10, 2012

The long history (and future) of white roofs

Unlike high-technology solutions to reduce energy use like light-emitting diodes (LED's) in lamp fixtures, white roofs have a long and humble history. Houses in hot climates around the world have been whitewashed literally for centuries now.

From a U.S. perspective, before the advent of central air-conditioning in the mid-20th-century, white and cream-colored houses with reflective tin roofs were the norm in places like South Florida. Then central air-conditioning arrived, along with dark roofs whose basic ingredients were often asphalt, tar and bitumen, or asphalt-based shingles. These materials absorb as much as 90% of the sun’s heat energy — often useful in New England, but less so in places like Texas. By contrast, a white roof can absorb as little as 10-15%.

"Relative newcomers to the West and South brought a lot of habits and products from the Northeast,” said Joe Reilly, the president of American Rooftile Coatings, a supplier. “What you see happening now is common sense.”

Around the country, roof makers are racing to develop products like those from Conklin in the hope of profiting as the movement spreads from the flat roofs of the country’s malls to the sloped roofs of its suburbs.

Years of detailed work by scientists at the Lawrence Berkeley Laboratory have provided the roof makers with a rainbow of colors, showing the amount of light that each hue reflects and the amount of heat it re-emits. White is not always a buyer’s first choice of color, so manufacturers like Conklin and others have used federal color charts to create “cool” but traditional colors, like cream, sienna and gray, that yield savings (though less than what purely white roofs do).

In an experiment, the National Laboratory in Oak Ridge, Tennessee, had two kinds of terra-cotta-colored cement tiles installed on four new homes at the Fort Irwin Army base in California. One kind was covered with a special paint and reflected 45% of the sun’s rays — nearly twice as much as the other kind. The two homes with roofs of highly reflective paint used 35% less electricity last summer than the two with less reflective paint.

Hashem Akbari of Lawrence Berkeley Laboratory says he is unsure how long it will take cool roofs to truly catch on. But he points out that most roofs, whether tile or asphalt-shingle, have a life span of 20-25 years. If the roughly 5% of all roofs that are replaced each year were given cool colors, he said, the country’s transformation would be complete in just two decades.

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Patton Services | (309) 303-3128 | rpatton55@comcast.net | http://www.whiteroofingsystems.com

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