Green roofs are extremely popular in Asia and Europe—particularly in Germany, where it's estimated that 10 percent of all flat roofs are green. They're also widely used in Switzerland, France, and Italy. Such is not the case in this country, however.
According to MSU's green roof research program, green roofs are less ubiquitous in the United States due to a general lack of awareness, limited quantifiable data about their benefits, and a lack of government incentives or tax breaks. “In Europe, [government officials] were able to apply public incentives and regulatory drivers to help stimulate the market,” Peck says, adding that the same has to happen here before green roofs will catch on.
To some extent, they already are. It's no accident that Chicago City Hall has a green roof: Mayor Richard M. Daley has vowed to make Chicago the leading U.S. city in the development of policies and programs that support green roof installation. Others—New York City, Washington, D.C., and Portland, Ore., for example—also have experienced an increase in green roof installations. In fact, a recent survey of GRHC members reported more than 80 percent growth in U.S. green roof square footage in 2004 and 2005.
Today green roofing systems are readily available from a number of manufacturers, including American Hydrotech in Chicago; Building Logics in Virginia Beach, Va.; and Weston Solutions, a Chicago-based company offering the GreenGrid roofing system for homes and smaller facilities. Despite their increased usability and ease of installation, Blau warns of one ongoing drawback: cost. Indeed, architects who are sold on green roofing and its benefits admit it's hard finding clients who can afford it.
The illustration (above) identifies the components of a traditional green roof.
“It's true a green roof costs significantly more than a traditional roof,” Peck acknowledges, “so there are barriers to use.” But if a builder is doing a subdivision, for example, there are obvious economies of scale, he adds. Some jurisdictions even offer public and private funding to promote green roofs, which he says can also lower the cost.weed whacking
As with most materials, green roofs bring their own unique challenges. Structural vapor considerations, for example, are important, especially if the roof will double as an outdoor space. “It's a little heavier, but it's easy to design [one] for a new house,” Blau says. “In a retrofit situation, there's more investigation involved.”
Design is important too. Alison Ewing, AIA, LEED AP, first designed green roof systems as a principal of William McDonough + Partners in Charlottesville, Va., so she's well-versed in the nuances of incorporating sod into elegant architecture. “The biggest concern for us is aesthetics,” says Ewing, now a principal at Hays + Ewing Design Studio, also in Charlottesville. “Integrating [the green roof] into the overall design idea is a challenge. It has to look seamless.”
Cobb agrees, noting that proper detailing will help a design maintain an appealing appearance. “I don't want to see scraggly weeds hanging off the sides, so the technical resolution of the edge of the roof is important to the overall appearance,” he explains.
Once such accommodations are made, the elegance and unlimited potential of green roofs become obvious. “It's important that we start constructing buildings that have a net positive impact on the environment,” Peck reasons. “A green roof is a way to do it.”