Flickr/Arlington County

A new tool visualizes green roofs on any building, and the water and energy they could save.

The rivers and streams advocacy group American Rivers has just come out with a cool new tool for what might seem an off-message topic: green roofs. A posterchild of the green building movement, green roofs have gained a lot of popularity in recent years with the rise of green building certifications like LEED, a high-profile roll out on the roof of Chicago's City Hall and the general uptick in concerns about energy usage in buildings. Growing a garden on top of your office building has rapidly evolved from crackpot to conventional.

To be clear: roofs ain't rivers. But the rain that falls onto roofs does find its way into water sources like streams and rivers, carrying with it the unfortunate and polluting residues of city living. This urban runoff includes garbage and motor oil and heavy metals and all kinds of bacteria and miscellaneous ickies that don't naturally occur in our waterways. Green roofs can help reduce all this by capturing the stormwater where it falls, using it to grow plants and sending the excess on its way without allowing it to pick up all that nasty urban grime from the vastly non-porous surfaces of the city.

With this in mind, American Rivers is trying to help explain how important green roofs can be. Its new tool allows users to simulate a green roof on nearly any building (or surface, to an extent) in Google Maps to see what sort of energy and water savings it could provide.

The site includes a few recommended roofs to re-imagine as green examples:

The White House, Washington, D.C.


358,723 gallons of stormwater runoff prevented from polluting the Potomac River each year
$16,974 in reduced heating and cooling costs

The Bellagio Hotel, Las Vegas, Nevada


630,398 gallons of stormwater runoff prevented from polluting the Flamingo Wash each year
$87,417 in reduced heating and cooling costs

Grand Central Station, New York, New York


1.2 million gallons of stormwater runoff prevented from polluting the East River each year
$68,499 in reduced heating and cooling costs

Here are a few other examples I selected:

Arizona State Capitol Building, Phoenix, Arizona


141,059 gallons of stormwater runoff prevented from polluting nearby water sources each year
$24,266 in reduced heating and cooling costs

The Pentagon, Arlington, Virginia


23.9 million gallons of stormwater runoff prevented from polluting nearby water sources each year
$1.1 million in reduced heating and cooling costs

Walmart SuperCenter in Bentonville, Arkansas


2.7 million gallons of stormwater runoff prevented from polluting nearby water sources each year
$179,300 in reduced heating and cooling costs

It's intended for buildings, sure, but there are plenty of other places that could be converted to green spaces. How much stormwater pollution and energy costs could they prevent? Let's look at the parking lot of that Walmart.

The parking lot of the Walmart SuperCenter in Bentonville, Arkansas


5.3 million gallons of stormwater runoff prevented from polluting nearby water sources each year
$359,795 in reduced heating and cooling costs

It's not exactly clear how much actual precipitation factors into these calculations, though the site claims that estimates are based on averages in nine regions in the U.S. The estimates, simply, are estimates. So while they shouldn't be swallowed outright, they do give an idea about what a green roof installation could do to help cut both energy costs and water pollution.

Images via: American Rivers; Google. Lede image courtesy Flickr/Arlington County

About the Author

Nate Berg

Nate Berg is a freelance reporter and a former staff writer for CityLab. He lives in Los Angeles.

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