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Green Roofs Sprouted 25 Percent More in 2006


This article was produced by BuildingGreen, Inc.- www.buildinggreen.com

Green Roofs

Photo: Green Roofs for Healthy Cities

The Mashantucket Pequot Museum and Research Center, in Mashantucket, Connecticut, features a 65,000-square-foot green roof over the museum’s exhibition space.

North America saw the installation of more than three million square feet of new green roofs in 2006, 25 percent more than in 2005, according to the industry association Green Roofs for Healthy Cities (GRHC). Steven Peck, president of GRHC, attributes the growth to an increased understanding of the benefits of green roofs, which has placed them at the fore of the current green building boom. “Green roofs have more benefits than any other green building technology in existence today,” he says.

Designers distinguish green roofs with two types. Extensive green roofs include less than six inches of growing medium and generally support only groundcover, such as grass, moss, and sedum. They are typically not accessible to building occupants. Intensive green roofs, on the other hand, include more planting medium—sometimes several feet—and can support a wide range of plants, creating a more park-like setting that is often accessible. Although about three square feet of extensive area was installed for every two square feet of intensive area in 2006, intensive green roofs are on a steep growth curve; extensive area grew 10 percent faster in 2006 than in 2005, according to GRHC, but intensive area grew 112 percent faster.

Regardless of type, green roofs offer significant benefits to a building and site. Since they absorb rainwater, green roofs reduce stormwater runoff. They don’t get as hot as conventional roofs, lowering internal cooling loads, saving energy, and mitigating the urban heat-island effect. Plants filter some pollutants from the air, so green roofs can improve air quality. Green roofs shield roof membranes from weathering while increasing thermal and acoustic insulation. Green roofs also offer aesthetic benefits while providing habitat for butterflies, birds, and other wildlife.

Green roofs contribute to several points in the U.S. Green Building Council’s LEED rating system. Sandra Liebowitz Earley, AIA, principal at Sustainable Design Consulting, based in Richmond, Virginia, says her firm includes green roofs in “a healthy percentage” of its commercial green building consulting projects, largely thanks to their LEED benefits. Also, she says, “they provide a great way for owners to ‘tell the story’ about their buildings’ green goals.”
Green roofs also have some drawbacks. “They add first cost to the building no matter how you slice it,” says Leibowitz Earley. She notes, however, that the cost premium can be reduced if green roofs replace other stormwater management devices. “A smaller challenge is that not all green roofs are visible or accessible,” she adds, and some owners “feel that the investment would be wasted without user appreciation.”

Peck says that effectively merging the nonliving parts of the building with the living roof is more complicated than people often assume. “Very few people have the multidisciplinary knowledge it takes,” he says. GRHC offers programs to build this knowledge in the design and engineering community, and the organization hopes to complete an accreditation program by the end of 2009. The availability of non-structural forms, often just simple plastic tray systems, for planting green roofs has also made it easier for architects to incorporate the technology into a roof with less need for unique details.

Despite the increasing popularity of green roofs, some misconceptions die hard. They don’t necessarily require additional structural support, for example. “Most green roofs in the Washington, D.C., area are only four inches deep, and I have never heard of one of those requiring added structural capacity,” says Leibowitz Earley.

Depending on the look the owner desires, green roofs don’t have to be irrigated or heavily maintained. Additionally, Leibowitz Earley notes, while leaks under green roofs can be especially problematic, it’s a misconception that green roofs are prone to leaking. And “yes, you can install them on sloped and curved roofs,” she says, noting that a 2:12 or 3:12 pitch is perfectly reasonable. “After all,” she notes, “in nature we call this a hill.”

– Jessica Boehland


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