December 8th, 2011
06:26 PM ET

Why we should all paint our roofs white

Editor’s Note: Vincent Valk is online editor for Chemical Week magazine. This post is part of the Global Innovation Showcase created by the New America Foundation and the Global Public Square.

By Vincent Valk – Special to CNN

Let us suppose, for a moment, that it were somehow possible to remove the greenhouse gas emissions of 300 million automobiles around the world – without actually removing any automobiles.

How would we go about doing this? A massive cash-for-clunkers style program in which everyone gets hybrids? A vehicle-miles-traveled tax? Something involving solar and wind farms?

No – we can paint our roofs white.

Cool roofs technology could also help building owners save on electric bills – about $360 per year for a thousand square meters of roof, according to a presentation at a conference at the Lawrence Berkeley National Laboratory (LBNL) in California in July of this year. This isn’t much, but it adds up, particularly if it’s hot out. Cool roofs technology would reduce energy consumption in over 90% of the territory of India, according to another presentation at the same conference.

If 80 percent of the roofs in urban areas in the tropical and temperate climate zones were painted white (or some other "cool" color, which reflects non-visible light), it would offset 24 billion metric tons worth of carbon dioxide missions. This is the equivalent of our 300 million cars, or of 500 medium-sized coal power plants.

Read more at the Global Innovation Showcase.

Hashem Akbari and Arthur Rosenfeld, researchers at LBNL, arrived at the estimate of 300 million cars by calculating the impact of the reduction of "solar heat gain" in buildings. Solar heat gain refers to the amount of energy absorbed by common dark-colored roofs, which heats up a building's interior and increases energy-intensive cooling costs. They found that painting 1,000 square feet worth of a roofs white offsets 10 tons of carbon dioxide emissions - scaling this up amounts to 300 million cars.

While large-scale white roof implementation would have a big impact globally, the local impacts vary depending on the climate. A 2003 study of eleven U.S. metropolitan areas by LBNL found that annual net energy savings would total $37 million in Phoenix, but just $3 million in Philadelphia. Still, savings are savings and all of it helps combat global warming.

Another presentation at the July conference discussed a new pilot project between LBNL, the Global Cool Cities Alliance (GCCA), the U.S. Environmental Protection Agency and the city of San Jose, CA. The project will involve the establishment of a "cool zone" in the city, with cool surface technologies, including cool roofs, deployed throughout an entire neighborhood. LBNL will monitor the impact of the cool surfaces on the local climate and energy consumption. The program may eventually reach the entire city.

Read: Using technology to stop "cattle-rustling".

GCCA itself, which was launched last year, has five "founding city members" on three continents, and is now working with R20, an association of regional governments aimed at developing low-carbon projects whose members represent local governments throughout the world.

Indeed, it is local communities that are taking the lead in implementing cool roof technology, and opportunities for that are practically limitless. Roofing and pavements (which are also typically dark colors) account for over 60 percent of urban surfaces. Roofs alone total about 20 percent to 25 percent. There are, literally, billions of square feet of dark-roofed surfaces in cities across the world, and white coatings are not difficult to find. It can take decades to scale hybrid cars or solar power; white roofs can scale quickly, as they require no new infrastructure aside from lots of white paint.

The ease of implementing cool roofs – which often literally means nothing more than painting roofs white – is what makes the idea so powerful, and attractive to communities. This is, unsurprisingly, especially true of communities with warm and sunny climates. California, to give one example, first required that new, flat roofs be painted white in 2005. The move was a no-brainer, according to Arthur Rosenfeld, author of the paper on global impacts change with Akbari and California Energy Commissioner when the rule came into force. "Everybody said…we should be doing this," he told me. Australia, too, has adopted solar reflectivity requirements – which, essentially, mandate cool roofs – in its most recent building code.

Read: How technology helped spur a quiet revolution in emergency aid.

Regulations have, thus far, mostly covered new roofing only, but most roofs need to be replaced about every 20 years, according to Rosenfeld, so they'll eventually have a big impact. Voluntary initiatives like New York City's NYC Cool Roofs, or the White Roof Project, which encourages people to identify roofs to paint white across the US and looks for volunteers to paint them, are working to whiten roofs before they need replacing.

"Our main goal isn’t coating the roofs ourselves," says Juan Carlos P.E., founder of White Roof Project. "We want people in cities across the nation picking up their own brushes, and creating change in their cities. We want to help people have the tools and support necessary to make this happen everywhere."

If, indeed, this does happen everywhere, it will be as though 300 million cars have disappeared, at least in atmospheric terms. This is a great thing, though you'll still be stuck in traffic.

The views expressed in this article are solely those of Vincent Valk. For more, explore the Global Innovation Showcase created by the New America Foundation and the Global Public Square.

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Topics: Climate • Innovation

soundoff (36 Responses)
  1. Adam

    Painting our roofs white will help us reduce energy costs in the summer because our homes won't absorb as much heat, lessening our need to cool our homes. Okay, sure. So do we all paint our roofs black again in the winter when we people want to heat their homes again?
    This white-roof idea seems shortsighted.
    Besides that, I think doing this kind of thing only obfuscates the main issue. As long as we keep doing things like this, such as painting our roofs white or planting a pasture atop our homes or some other kind of "green" innovation, people will continue to think that nothing is wrong and that we can just keep on doing what we're doing.
    The end-result that I see coming out of this is people thinking, "Well since we're saving so much energy here, let's just expend more over here."
    Am I right or am I myself being shortsighted?

    December 8, 2011 at 8:42 pm | Reply
    • jenks

      hey buddy, ah... you wont have to paint your roof black in the winter. the sun does not heat your home in the winter. its too far away. your furnace does. that being said, it wouldnt matter what color your roof was in winter.

      December 9, 2011 at 2:06 am | Reply
      • Tim

        Winter does not come because the earth is far away. It comes because of the tilt of the earth's axis, which causes the same amount of sunlight to be spread out over a greater area, which means less heat.

        I agree that the furnace heats the house, and your roof probably has snow on it anyway. Painting all the roofs white is a good thing. Please just make sure the reasoning you give behind it is correct.

        December 9, 2011 at 11:42 am |
  2. Andokari

    If painting your roof is the only thing that people need to do to reduce carbon emissions, than i‘m all for it.

    December 9, 2011 at 5:13 am | Reply
  3. Coprolito

    Is it possible to cover the roofs with retractable white/black awnings depending on the season?

    December 9, 2011 at 4:16 pm | Reply
  4. David

    Of course solar gain heats your house in the winter.

    The numbers of savings are grossly overestimated. I live in the South and pay far less than what painting my roof would miraculously save.

    And is painting asphalt really a reasonable idea? No.

    I have a radiant barrier – which basically saves about the same. And it saves about $50 a year. If I didn't have ductwork in the attic, it would be more like $10 a year.

    Just imagine how good the paint would look as the asphalt gradually breaks down.

    December 12, 2011 at 8:02 pm | Reply
  5. James J. Roper

    With the white roofs, the sunlight will be reflected back into the atmosphere, thereby heating the atmosphere more. It is similar to what causes desertification – the increased albedo of the soil (as compared to plants) reflects light, which then heats the atmosphere, which is also equivalent to drying it out a bit. Hotter atmosphere, less rainfall. So, the change in albedo, and the consequent change in atmosphere temperature, needs to be included in the model.

    December 14, 2011 at 10:54 am | Reply
  6. Thomas

    Why all of this save energy here and there? All while we push for more Electric vehicles on the road? We still have rolling black outs in Texas during high usage Winter and Summer months. Just think if everyone had a da_n car plugged in to your outlet in the garage demanding EVEN MORE ELECTRICITY! What is wrong with this nation? PICK SOMETHING AND GO WITH IT! Either cut electrical energy usage, or don't. Pushing hybrids and other electrically demanded vehicles will exponentially increase energy usage requirements passed what is already in place. Households in American cannot come close to cutting enough energy usage to support the demand for an electric vehicle to sustain current usage. Now we need to paint our roof to save $360 for 1,000 sq. meters of roof area. Well in my neighborhood, that would be less than $12/yr per household. How much does this paint cost? How long will it take to recoupe the costs of such effort? 20+ years? 30+ years? Anything to make a buck, take from the middle class to give to the rich. GO F_CK YOURSELF ENTREPRENEURS!

    January 3, 2012 at 5:24 pm | Reply
  7. Nick

    i notice the article mentions hot or temperate climates and references california and australia. what about places farther north? Canada? Michigan? Minnesota? Scandinavia? does it have a reverse effect on heating costs in the winter? plus wouldnt this just heat the air up even more?

    January 30, 2012 at 5:15 pm | Reply
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    July 3, 2012 at 6:35 pm | Reply
  9. gary

    the reasoning behind painting your roof white isn't only to save in cooling costs.
    it's also to lower the temperature of the outside air.
    that cools the whole area.
    re-read the story.
    or "google" this idea and try to understand the concept.
    it's like some people are so proud they get 14 mpg because... they can.

    August 2, 2012 at 2:48 am | Reply
  10. Joe

    If you live in an area with more heating degree days than cooling degree days the theory makes sense. If you look at northern tier states like MI there are a bunch of white roofs. However if you drive south from Detroit and go to Windsor Ont they are all black. Why? White will cost the owner money when heating the building.

    September 20, 2012 at 10:17 am | Reply
  11. lyn

    The white paint would reflect the heat into the air adding to the earth warming! A better idea is to add dirt to the roof and throw grass seed on it, this would consume carbon dioxide and insulate the home!

    October 5, 2012 at 9:58 am | Reply
  12. Beacon Home Inspection Services

    The number one reason not to paint your roof white. As a Home Inspector I see all types of methods for cooling your attic and saving on energy costs. I can't speak for all areas of the country but out of all of the homes that I've inspected in the West Palm Beach area with roofs painted with this white elastomeric type material everyone of them have a much higher content of visible mold. While it does tend to cool the attic considerably it also changes the thermodynamics inside the attic which appears to be more conducive to mold growth. When you cool the attic the air movement in the attic is drastically reduced. When roofs are designed the venting is designed with the attic temperature in mind. Air is circulated through the attic using convection, convection is achieved by temperature differentials (hot air rises and also moves to the cooler areas of the attic around the vented areas) it trys to equalize pressure by equaling temperature. When you cool the attic by painting it white that equalization process and all air movement comes to a halt. If this lack of air movement isn't accounted for and offset by a powered electric ventilation system moisture builds up in the attic causing conditions that are highly conducive to mold growth. The costs to paint your roof, install and power an electric ventilation system can quickly offset any savings or green energy initiative ideas one may have. If you have HVAC ductwork or your HVAC air handler up in your attic and you have air leaks in that system you may inadvertently pump mold spores into the living quarters of the home and that could cost you ten of thousands of dollars in hospital bills and or remediation costs.

    November 23, 2012 at 5:02 pm | Reply
    • Chen

      Hi, I saw your comment on roof painted white tends to grow mold. I have the exact problem. A roofer installed flat roof in 2012 then coated it with white solar reflective paint right after couple of raining days. Earlier 2013 during the raining season, I saw a lot of black mold on the plywood under the flat roof. The area at the time was exposed to the air without an attic yet. Why did the mold grow? I now have removed the mold w/ HomeDepot chemicals and installed an attic under with baffles and insulation. Do you think the problem will come back in the next raining season? Please contact me or leave your contact info. Thanks.

      July 5, 2013 at 4:14 pm | Reply
  13. Alfonso Haymaker

    Wind power is the process by which wind is used to generate power or electricity. The power of the wind is actually a form of solar power – wind change and variability is caused by uneven heating of the ground by the sun. In order to fully use the power that the wind is capable of generating, many countries have set up wind farms. In a wind farm, many different wind turbines (a structure that uses a propeller-like blade to take in the wind’s power) are set up in an area. With all the wind turbines working at the same time, it’s thought that these farms are a great way to produce large amounts of electricity. ,

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    April 16, 2013 at 10:07 am | Reply
  14. Rayford Blackham

    The upcoming hybrid cars promise to be even better than the ones that are already available. Hybrid cars are designed with the environment in mind, and the savvy car companies know that the highest prizes will go to those companies that can design an outstanding car that is easy on the consumer’s pocket as well as the world around us. Car manufacturers are investing untold amounts of money on the creation of new and upcoming hybrid cars. With the advent of the totally electric car still on the distant horizon, motor companies are currently competing to make sure their own hybrid cars produce the lowest amount of emissions possible.`,;;

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    May 19, 2013 at 2:56 pm | Reply
  15. Mae

    I don't find painting my roof why neccessary, but thanks to this post. it somehow enlightens me http://geothermalcompanies.org/

    May 23, 2013 at 10:14 am | Reply
  16. looncraz

    Instead of painting roofs white, or black, or whatever, I'd suggest to cover the roof with a removable sheet.

    You would use the sheets in the summer, but not in the winter. You could even create an automatic heat-triggered system – if the interior temperature was warm enough, the sheets would unroll and reflect more heat. If too cold inside, the sheets would roll away.

    Wouldn't be all that hard, but would probably run a few grand a roof...

    December 5, 2013 at 4:39 am | Reply

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