Want a White Roof for Your House?

| 8/18/2009 12:13:19 PM

Tags: white roofs, question to readers, cool roofs, global warming,

White roofs, aka cool roofs, have caught attention lately as an offbeat but relatively simple and effective strategy for reducing air conditioning costs and greenhouse gas emissions.

The idea is simple: white reflects heat instead of absorbing it. It's also a favorite idea of Energy Secretary Steven Chu, who said "when you're thinking of putting on a new roof, make it white" in his appearance last month on The Daily Show with Jon Stewart (you can watch the video below).  Chu added that white roofs costs about the same as traditional black roofs and for those in a warm climate, a white roof can reduce air conditioning costs up to about 20 percent.

When Chu talks white roofs, he cites research from Art Rosenfeld, the commissioner of the California Energy Commission. Rosenfeld calculated that pervasive white roofs and white streets throughout the United States would create a significant reduction in carbon dioxide emissions — the equivalent to getting rid of all cars for 11 years. You can learn more about Rosenfeld and his passion for energy efficiency by watching the second video below.

The New York Times also covered cool roofs in White Roofs Catch On as Energy Cost Cutters.

"We come home on days when it’s over 100 degrees outside, and the house is at 80 degrees,” white roof owner Jon Waldrep of Sacremento, Calif., told The New York Times.  

According to research by the Lawrence Berkeley National Laboratory, nearly every state could see significant reductions in carbon dioxide emissions if 80 percent of commerical buildings were converted to have white roofs, even if white roofs meant increased heating demands in winter. You can see how much each state would save in Imagining a Cool-Roof Nation.

R S_5
3/14/2011 8:05:51 AM

rThe purpose of a roof is to keep weather, varmints and insects out of the insulated box where you live. An ideal attic temperature should match the outdoor air temperature. Insulate and ventilate attics/roofs properly and roof color should have little effect on your HVAC performance. A white roof will reflect sun light, but it also doesn't radiate heat as much as a dark roof in non-sunlit situations (black body radiators, for the engineering/scientifically oriented readers). In other words: a dark roof will heat an attic space more in the sunlight, but will then radiate more heat out when the sun's warming rays are not present. A dark roof's attic space temperature will swing to higher highs and lower lows than a similar more reflective roof's attic. In the shorter winter daylight hours, a dark roof will radiate more heat than it absorbs from the sun. If your attic/roof isn't insulated and ventilated properly, then a dark roof costs you more HVAC money, year round, whether you're in the far north or deep south. A few words to defend the choice of a lighter color/reflective roof: Due to the smaller temperature swings, there is less expansion and contraction of a reflective roof surface and structure. Ie: Similar light color roofs last longer than darker ones. A side note: over-insulation is possible. Don't waste your money and time on too much insulation. The laws of diminishing returns for insulation products kick in sooner than you may think.

2/9/2010 7:33:19 AM

I recently installed Santafe clay roof tiles in Frost color (a white glazed roof tile) It is great because it has the benefit of the high solar reflectance and thanks to its ceramic finish it's virtually maintenance free! go to http://www.santafetile.com and select "Green Roof"

Bob R
8/30/2009 12:07:05 PM

Okay, I think we all agree that a reflecting roof covering could be an important consideration. But as Roger pointed out, roofs get dirty, and this would cancel out the benefit, would it not?

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