White Roofs Are 3 Times More Efficient Than Green Roofs

Rooftop vegetation looks awesome, but it isn't the most environmentally friendly choice out there.

Everyone loves a garden, and when the vegetation is planted on a roof, it gets even more love. Not only do plants lend a park-like atmosphere to the tops of buildings, they are also good for the environment. Look at all these plant-covered roofs in New York City. Even buses are getting in on the trend.

Turns out, though, that a plain white roof is way better for the environment. A new study in Energy and Buildings points out that while green roofs are better than roofs painted black—which absorb sunlight and contribute to the urban heat island effect—white roofs can actually combat global warming by reflecting more sunlight back into the atmosphere. Based on an economic analysis of the costs and benefits of the three types of roofs, the researchers at the Lawrence Berkeley National Laboratory found that white roofs are three times more effective at fighting climate change.

That’s not to say you should go and dig up the sedum and trees on your roof. Vegetation helps with storm water management, and studies have shown that being near greenery can make us happy. But if you’re really looking to save the environment, consider a fresh coat of white paint.

[H/T: Popular Science]

[Image: White roofs via Shutterstock]

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7 Comments

  • For over a decade, The EPDM Roofing Association (ERA) has been the leading researching body and voice for manufacturers of both white and black EPDM single-ply roofing systems.

    Based on our concern that this study, released by Lawrence Berkeley National Laboratory, is flawed, ERA assembled a team of experts to provide analysis of the study and detail its extreme shortcomings. Their analysis found that the LBL Researchers failed to follow certain scientific processes, and that the report frequently relied on anecdotal data, potentially biased or incomplete interpretations of data, and lacked quantitative sources of data. The complete analysis can be found at http://www.epdmroofs.org.

    Furthermore, ERA rejects the recommendation contained in the study that black roofing be banned in warmer climates. Due to the complexity of roof and building science, prescriptive requirements that limit choices available to the architectural and building owner community are not in the best interest

  • I am one of the study's authors. Thank you for your coverage of our article. Our study finds that white roofs are more cost-effective over 50 years than green roofs. We do not reach a conclusion about which is most environmentally beneficial. It is true that one factor our analysis considers is the direct global warming offset potential from reflecting sunlight back into space, for which green roofs are roughly three times more effective (rather than efficient) than green and probably about five times more than black. Any roof that saves on air conditioning energy more than it loses on heating energy, like either white or green roofs in warm climates, will bring indirect climate change benefits from reducing power plant emissions. Still, green roofs offer many environmental benefits that are difficult to monetize for an economic assessment.

    While the paper on ScienceDirect is paywalled, I can provide a copy upon request (email BHMandel@LBL.gov). Thanks for your interest!

  • Lloyd Knowles

    Richard and Alexis are absolutely right. Mind you, a study can be found that will give you any conclusion you want - therefore the sources should always be checked! The jump from an economic analysis to fighting global warming is.... well, crazy. There is no actual proof that mankind can slow down global warming. For that matter, they can through a lot of numbers at it (and I'm not saying that we haven't played a role) and come to any conclusion they want. Numbers are funny that way. But proof of the human race have control over changes either way in the global environment cannot be proven.

    As for green roofs: as an architect I have specified a lot of white roofs. Why? Because they are cheaper than green roofs and need less maintenance. These decisions are made by developers; again just of the basis of up front economics. Personally, I would always recommend a green roof. Better for the environment and the life cost of the building.

  • White roofs save on cooling costs. Black roofs save on heating costs, so are the wise choice in northern climates. Stanford University study shows white roofs actually increase earth's temperature by reflecting heat upward and mixing with soot, thus contributing to global warming.

  • Richard, your comments on this article hit the nail on the head. One of the reasons urban heat islands exist is the displacement of natural vegetation and landscape with man-made concrete and asphalt. Reflective roofs only serve to reflect sunlight and heat back into the atmosphere. The Copper Development Association did a study and found the water temperature in copper HVAC pipes above a white roof were hotter than over a black roof. White roofs make more sense in the deep south where they consume way more energy to keep cool. In the central and northern parts of the country it is not unusual to consume 3 to 5 times more energy trying to stay warm. The heating penalty with a white roof in a central to northern climate is greater than the cooling benefit and will therefore consume more natural resources and only add CO2 emissions. The ENERGY STAR program recommends people use the Roof Savings Calculator to see if a white roof will end up costing you more money.

  • Richard Hayden

    Shaunacy; This article completely misses the point that was made in that study. While white roofs may reflect heat, green roofs absorb the suns rays and through evapotranspiration, cools the surrounding environment. White roofs cannot do that. Green roofs also reduce the amount of rainwater that leaves the roof through evaporation (from the media) and evapotranspiration (from the plant materials). The result is less stormwater. White roofs cannot do that. Green roofs also delay the release of that stored rainwater because of the medias used in the green roof assembly. This delay helps storm sewer systems immensely. White roofs cannot do that and in fact, white roofs accellerate the flow of water into already over-taxed storm sewer systems.
    And there is strong evidence that in northern climates, white roofs actually increase the amount of energy required to heat buildings by reflecting the sun's energy away from the buildings that rely on the sun for heat gain.