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Buildings Image Credit: Columbia University

Published on June 10th, 2014 | by James Ayre

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Green Roofs = Cost-Effective Means Of Preventing Sewer System Overflows

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June 10th, 2014 by  

Green roofs are a cost-effective means of preventing sewage system overflows, according to new research from Columbia University.

Image Credit: Columbia University

Image Credit: Columbia University

The ability to stop overflows of course stems from the fact that green roofs retain water and thus prevent said water from simply flowing into the sewers.

As an example, the green roof on top of the Con Edison building in Long Island City, Queens (investigated by the researchers) — home to around 21,000 plants — retains roughly 30% of the rainwater (on a quarter acre) that falls on it. That’s a pretty significant amount of water.

The press release from Columbia University provides more:

If New York City’s 1 billion square feet of roofs were transformed into green roofs, it would be possible to keep more than 10 billion gallons of water a year out of the city sewer system, according to the study led by Stuart Gaffin, research scientist at Columbia’s Center for Climate Systems Research.

New York City, like other older urban centers, has a combined sewer system that carries storm water and wastewater. The system often reaches capacity during rains and must discharge a mix of storm water and sewage into New York Harbor, the Hudson River, the East River and other waterways.


The Con Edison Green Roof was built (and research on it began) back in 2008. An adjoining “white roof” was also constructed.

Previous to these new findings, the researchers had already determined that the green and white roofs were quite effective at reducing energy costs and, also, urban air temperatures.

“The information we are collecting from Con Edison’s roofs is invaluable in helping us determine the costs and benefits of green infrastructure projects,” Gaffin stated. “Without solid data from experiments like this, it is impossible for us to know which projects are the best options for protecting the environment.”

When you take into account the cost of building and maintaining a green roof, the cost of capturing rainwater works out to about 2 cents a year to capture each gallon of water.

We’ve also reported previously that green roofs and solar panels are a great fit. Green roofs help to keep the solar panels cooler, which boosts their efficiency. For more on that, see one or all of these three stories:

Green Roofs Pave the Way to Cheap Solar Power

Green Roofs & Solar Panels: The Future of Renewable Energy?

Green Roofs Boost Solar Panel Performance

In related news, a similar “simple” solution to the management of high urban temperatures was recently put forward as a solution in Australia — white roads. While the concept of using white roads to reflect light and thereby reduce temperatures is certainly nothing new, it hasn’t yet been applied on a truly large scale, something that the Cool Change Cities Project is setting out to do.

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About the Author

's background is predominantly in geopolitics and history, but he has an obsessive interest in pretty much everything. After an early life spent in the Imperial Free City of Dortmund, James followed the river Ruhr to Cofbuokheim, where he attended the University of Astnide. And where he also briefly considered entering the coal mining business. He currently writes for a living, on a broad variety of subjects, ranging from science, to politics, to military history, to renewable energy. You can follow his work on Google+.



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