Green Roofs: Building for the Future

From the U.S. Food and Drug Administration building in Washington D.C., to Heinz Corporate headquarters in Pittsburgh, an increasing number of buildings are swapping shingles for sedums. The movement is called green roofing, but far from an industrial paint job, it evolves around technology that's ecologically sound -- and proving so useful that cities like Portland, Ore., Chicago, Boston, Seattle and the entire state of Maryland are eagerly exploiting the potential of this once-forgotten façade.

"This technology offers us an opportunity to significantly improve not only the way our buildings operate, but to utilize wasted spaces -- there are millions of square miles," says Steven Peck, founder and president of Green Roofs for Healthy Cities, an organization established to increase awareness of green roof benefits. GRHC also hopes to advance the market in North America. "The roofing industry is just at the beginning of a process of transformation. Nothing can match the range of social, economic and environmental benefits green roofs provide."

As the name implies, green roofs are roofs made of plants. They're comprised of a waterproof membrane followed by a root barrier, a drainage layer and finally the growing medium and a variety of plants, grasses, sedums, cactus or shrubs -- hence, the green. The technology, of course, isn't entirely new. For millennia, the natives of Scandinavia and Iceland, particularly barren environments with limited building materials, used sod on their roofs as insulation; in Tanzania, mud huts with grass roofs are common; and closer to home, many early settlers used sod to insulate their walls and prairie grass to cover their roofs.

Green roofs today

In more recent years, Germany spearheaded the modern movement back to grassy rooftops, but this time with an urban twist. During the 1970s, the densely populated country began installing green roofs to prevent storm water from surging into its aging sewer systems, and the industry has since boomed, experiencing rapid and sustained growth. Today, roughly 14 percent of the country's total roofs are greened, the industry continues to grow 10 percent per year and some German cities actually levy a "rain tax" on nongreened asphalt rooftops.

Germany's pioneering work has encouraged other countries such as Australia, Japan, Mexico, the Netherlands, the United Kingdom and Switzerland to actively embrace the concept. But there's more to the mounting buzz than sheer novelty. In an era when global warming, catastrophic weather patterns, flooding, sustainability issues, and man's very tangible impact on the planet's health grab daily headlines, green roofing offers positive solutions.

"If you pick up a newspaper every day, sometimes you don't want to lift your head out of bed. Good news doesn't always make the news. But green roofs -- it's encouraging stuff," says Ed Snodgrass, a horticultural consultant who owns and operates Emory Knoll Farms, a nursery specializing in green roof plants. Snodgrass recently covered the Library of Congress' 100,000-square-foot top. "In the cities there's not much opportunity to do things down below, so now we're trying to do it up above!"

Why it works

The benefits of green roofs are extensive. The primary advantage, and what initially spurred German research, is that it helps mitigate storm water runoff, a problem that costs millions every year. In cities, with thousands of square meters of solid, impermeable asphalt and concrete surfaces, when it rains, it literally pours -- straight into drainage pipes, which then empty into the sewage system. Too much water too fast, the system can explode, leaking raw sewage.

But green roofs retain or absorb rainwater much like a sponge, slowing its flow, and according to Brad Rowe, associate professor of horticulture at Michigan State University, which boasts its own green roof research program, retain between 60 and 100 percent of rainfall, depending on its intensity and duration. "Sixty percent is a surprising average. The normal roof might hold only five percent," he says.