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?

Peter Glunz
8/28/2009 2:45:27 PM

Global warming... It is not only a question of saving 20% on the energy bill because of less need for airconditioning (as only a fraction of the heat is travelling into the house because of the insulation) but the whole (black?) roof is a giant solar collector which is transforming the suns IR-radiation into heat causing higher air temperature. A white roof will reflect the IR-radiation back into space and not convert it into heat. This primary saving on global warming seems to be much greater than the savings on less energy production. Funny that I havn't seen this aspect in all the comments? With best regards from Denmark - www.glunz.dk

8/26/2009 3:44:23 PM

thanks for that link, April!! excellent i'd go with a white roof on our funky old house here in west TX, but April's link shows that's not necessary. you CAN have your colors and your reflectivity, too. :D

8/24/2009 7:44:42 AM

In Bermuda, all the houses have white roofs, by law. There is no (or very little) fresh water in Bermuda, so everyone must catch and store their own water. The roofs are painted with lime based paint to prevent mildew and mold. I lived in a Bermudian house for a while and found it to be very cool because of construction materials, the water catchement, and the white roof.

Pat Miketinac
8/23/2009 9:15:09 PM

Another option is to coat a dark roof with a product like Kool Seal. I even used it on roll roofing here in FL. As for mildew, I just mop bleach on it if needed, which is easy if it has a low slope, but bleach is slippery. There is also a radiant barrier paint that is applied to the underside of the roof from the attic.

Kandi Newell_2
8/23/2009 2:15:44 PM

Although I'm all for anything that will help the environment, however along with the aesthetic factor, the very fact that white reflects could pose problems as well. The reflection itself is blinding as I can attest to. A neighbor has a metal roof that reflects the noonday sun directly into my Grandmother's porch. Now her porch is much hotter + it is blinding anyone who cares to relax during those hours of the day. I also read that white was a possible color choice for future roads, another potential hazard due to the reflection. Ask any skier about the reflection off the white snow, it's blinding.

8/23/2009 3:36:18 AM

I originally intended to have a white roof, but in the wet tropics they rapidly acquire a grey cover of mold which undoes the good work. I finally would up with a red roof which has no trace of mold after 15 years, the decision was mainly made by my wife for cosmetic reasons, but it has turned out to be sound. It is probably still more efficient than a white roof turned grey/black.

Bob R
8/22/2009 12:41:18 PM

My home is in a heavily wooded development in North Florida. The asphalt shingle roof is 22 years old. It gets sun all day so it gets quite hot and radiates heat to the attic floor. I definitely am thinking of reflective shingles or metal. The "white" thing is a problem because my house and fences are painted brown. Roofs are designed to vent moisture, but this venting is not really sufficient to cool the attic, so a power vent fan is advisable. Another thing would be to line the underside of the roof deck with foil. Easier said than done unless you do it at the time the house is being built. I will definitely blow in more insulation and try to cover the flex-duct that distributes the conditioned air; the air in the duct gets quite warm when blower is not running, and then all this hot air is blown into the house when A/C comes on again. Understand: radiation, convection, conduction.

8/21/2009 12:49:38 PM

Regarding cold weather areas, black roofs absorb heat better during the day, but they also radiate house heat away more effectively at night; white roofs would still provide the benefit of keeping the house cooler in summer, when the sun is directly over head, and in winter would provide the additional benefits of slowing snow melt and lessening heat loss, especially in under-insulated houses.

D Hutchinson
8/21/2009 9:56:33 AM

We have an earth roof 3' deep which insulates superbly. Our carport & barn have terra cotta propanel roofs. We are considering lighter roofs, perhaps pale gray, for the out buildings. We are in sunny NM & the carport & barn are not set up for heat or cooling. It would make a great difference during the summer.

Mary R
8/21/2009 9:52:34 AM

I live in the desert Southwest and yes, I would definitely have a white roof. This year the airport is giving us energy efficient windows, doors and insulation to offset the noise they make flying overhead (the house was here 30 years before the airport). Once they are done, we have a few other fixes to make to this old house. We are thinking about painting the shingles, which are still in great shape, with one of the cool white elasto coats common to this area. I figure it is not green to replace things that are doing their jobs when they can be tweaked. When we do replace the roof, I want a standing seam white coated metal roof with solar panels. Ok, I may never be able to afford the solar panels as long as I have to pay for them upfront before getting the rebate, but I can dream.

Alex McKenzie
8/21/2009 8:17:48 AM

I just had a new roof put on my house, and while I didn't go with a white roof, I went with a fairly pale mottled grey. As it turns out, I like it more than the old dark charcoal grey/black I had before. A lot of the benefit of a white roof, though, depends on where you are. If you're in Texas, yes, you're going to see a benefit. If you're in northern Maine, or Washington State, though? Well, maybe you're not going to see such a big difference. If your hot season is short enough, and you live in an area that doesn't get a lot of snow, a dark roof may be better. Around here, the roof stays covered in snow for most of the winter and into the spring, so having a dark roof really doesn't provide much benefit.

8/19/2009 11:56:48 AM

You no longer need to have a white roof to reflect the suns rays. CertainTeed just came out with new product called Solaris - solar reflective shingles, and it is available in 4 traditional colors. Check it out http://www.certainteed.com/products/roofing/residential/designer/317920.

Kathleen McKinley_2
8/19/2009 2:24:51 AM

Although I think having white roofs on flat-roofed commercial buildings or even flat-roofed residences would be fine, I think white roofs on most residences with pitched roofs would be extremely ugly. I wouldn't want one on my house and I'm not sure I'd want to look at them on others' houses. Where I live, air conditioning is completely unnecessary, and is rarely used except in commercial buildings with windows that can't be opened, so I don't think switching to white roofs on residences would have a big impact on energy use for air conditioning. In fact, where I live, keeping the house warm in cool whether is a bigger problem than keeping it cool in warm whether, so to the extent that a dark roof keeps my house warmer, I'm happy with that. And to the extent that it reduces my need to run the furnace, I think that's an environmental (and financial) benefit which may counterbalance the benefit of switching to a white roof to keep the building cooler in hot weather. Other than reducing carbon emissions by reducing the need to use air conditioning, are there any other environmental benefits of reflective white roofs? And do those benefits really outweigh the ability of a darker roof to help keep a building warm in colder whether?

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