Green Roofs Playing a Greater Role in American Cities

Green roofs are originally a phenomenon of Europe, but have been playing an increasingly greater role in the US since 1997, according to research published in the June issue of Environmental Health Perspectives (EHP).

According to the study, green roofs are "rooftops that are partially or completely covered with vegetation growing in soil medium over a waterproof membrane." They are important because they boost energy efficiency and reduce ecological harm by controlling stormwater runoff. Green roofs are in the limelight because the EPA, design and development consultancy and advocacy groups, and prominent cities are accelerating the installation of green roof projects and the implementation of green roof policies and practices.

The study says the EPA is currently working on a report detailing national policies and practices relevant to green roof projects and incentives. It has been suggested by consultancy and advocacy groups that the EPA might include green roof incentives as part of the Clean Water Act.

Facts Favoring Green Roofs

Rivers, estuaries, and bays are being harmed by silt, which settles over natural sediment. This causes ecosystem deterioration and water turbidity. Most of the erosion that produces silt occurs because of rainwater and other stormwater runoff, the EHP study said.

Finding a way to decrease runoff will aid in restoring waterway health. The Potomac River, the Anacostia River and the Chesapeake Bay have increased turbidity from an increase of silt from runoff. The study said that Doug Siglin, who directs the Washington, D.C., area Chesapeake Bay Foundation, explains that green roofs reduce runoff by redirecting stormwaters.

A March 2007 report by the non-profit consultancy group RESOLV gave major emphasis watershed health, with sub-watersheds as an additional priority. A watershed is all the tributary and other sources of runoff being fed into a river. Sub-watershed areas are those secondary areas bordering the watershed.

A more immediately pressing problem is that of the "heat island" effect. According to the EHP study, the heat island effect describes the phenomenon that cities can have temperatures 10 degrees Fahrenheit higher than populated outlaying areas. Chicago has had serious heat-waves in recent years that were amplified because of the heat island effect. Chicago's commissioner for the environment, Sadhu Johnston, explains that green roofs make buildings up to 31 percent cooler than conventional roofs. EHP cites Johnston as saying that green roofs can "help avert heat-wave-related deaths."

Benefits of Green Roofs

Because of the heat island effect, many benefits are realized when cities change from conventional roofs to green roofs. As Johnston explained to EHP, because buildings with green roofs stay cooler, energy consumption and costs stay down.

This avoids consumption demands that spike in the worst of the summer months. The air pollution levels that also spike are similarly moderated. These benefits are of paramount importance, but of even greater importance is the public health benefit.

The EHP study quoted Johnson as saying that green roofing would help to avert heat-related illnesses. The study lists these illnesses as heat exhaustion and heat-stroke, with the worst being heat wave-related deaths. Cooler buildings and a cooler neighborhood with many green roofs would make a quantifiable significant difference in public health. This is particularly true as hotter summers result from global warming.

History of Current Green Roof Practices

While there was some talk of "garden rooftops" in the 1970s during the energy crisis, nothing in particular came of it. It went the same way as all the other U.S. innovations accommodating limited fossil fuels, like smaller gas efficient cars and alternate energy cars. But beginning in the late 1990s, new interest brought back the idea of "garden rooftops." This time they are called "green roofs" and are inspired by European practices.

The EHP study says that Tom Lipton of Portland, Ore., who is an environmental specialist, is the first to re-invent the American green roof. He did so after a trip to Europe. He converted his garage roof to a green roof and for two years measured rainwater runoff. He did this with an eye to addressing Portland's stormwater runoff erosion and control problem. As a result, Portland added green roofs to its list of favored building development practices.

In 1999 Chicago's mayor Richard Daley, Jr. returned from a trip to Europe inspired by the green roof practices he also saw there. He re-roofed City Hall with a green roof. Now, Chicago has 300 buildings with green roofs. In 2004 the nonprofit group DC Dreamworks installed a green roof demonstration model in Washington, DC that has drawn more than 3,000 visitors and inspired green roof projects throughout D.C.

Most significantly, a Washington, D.C. court ordered a settlement payment by the D.C. Water and Sewer Authority for the sum of $300,000 to D.C.'s District Department of the Environment (DDOE). This settlement marked the beginning of the DDOE's serious consideration of green roofs for rainwater and stormwater runoff control. This money was issued in grants, along with an incentive package, to developers for designing and implementing green roof projects.

Now, cities and counties like York City, Bronx, Brooklyn, and Harlem, Minneapolis, Los Angeles, Atlanta, and Montgomery County, Maryland, have or are beginning to have green roof projects and incentive packages. Taylor reports that the city project developers say they are spurred on by the competition between the cities. Each of these cities wants to be the greenest city in America, including the nation's capitol, Washington, D.C.

David A. Taylor, "Growing Green Roofs, City by City". Environmental Health Perspectives. URL: http://www.ehponline.org/