It’s been pretty well established that in terms of rooftop “color,” a tried and true tired shade of black won’t win a homeowner any sustainability cred given that they run up AC bills, negatively impact the health of those living beneath them during heat waves, and warm up entire cities and towns.

Totally and truly not cool.

So what’s better for the environment? Painting a rooftop white or hauling a bunch of vegetation up there to create a green roof?

According to a recent report titled “Economic Comparison of White, Green, and Black Flat Roofs in the United States” to be published by the U.S. Department of Energy's Lawrence Berkeley National Laboratory in an upcoming volume of the journal Energy and Buildings, while insulating green roofs are aesthetically pleasing and a decent source of bragging (how many of your neighbors are growing plants on top of their townhouses?) they’re also less cost-effective over a 50 year lifespan, more high-maintenance, and do not offset climate change in the same manner as their white-coated brethren. In fact, solar-refective white roofs are three more times effective at countering global warming in cities than green roofs according to the study.

Still, green roofs are a far superior alternative to black roofs and, when it comes down to it, can help homeowners better save on energy bills than white roofs can as a leafy cover insulates a building during the cold months and keeps heat out in the summer.

To be clear, the study examined 22 commercial flat roof projects and did not take into consideration flat and non-flat roofed residential properties although the lessons learned from zeroing in on commercial buildings can certainly be carried over to single-family homes and multi-family developments.

An abstract of the study boils it down to a choice between global warming and “local environmental benefits:”

Owners concerned with global warming should choose white roofs, which are three times more effective than green roofs at cooling the globe. Owners concerned with local environmental benefits should choose green roofs, which offer built-in stormwater management and a ‘natural’ urban landscape esthetic. We strongly recommend building code policies that phase out dark-colored roofs in warm climates to protect against their adverse public health externalities.
On that note, study co-author Arthur Rosenfeld, the recipient of the 2012 National Medal of Technology and Innovation and a guy who really knows his cool roofs, elaborates on the health impact of black roofs:
In Chicago’s July 1995 heat wave a major risk factor in mortality was living on the top floor of a building with a black roof. White doesn’t win out over black by that much in economic terms, so government has a role to ban or phase out the use of black or dark roofs, at least in warm climates, because they pose a large negative health risk.
Interesting stuff. I’d be curious to see if black roofs were indeed phased-out in target cities if there would be a whole bunch of Republican-lead fussing and resistance a la incandescent light bulbs — a flat roof revolt, if you will. It’s certainly a possibility as folks don’t like having the government taking away the “traditional” option even if it means a healthier planet and, in the case of black roofs, a healthier person.

Via [Popular Science] via [Grist]

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