Lexus Website, Spring 2004

Higher Ground

Green roofs are germinating in the city.

For square-footage-starved city dwellers, gardens are few and far between — limited to the box of herbs on the kitchen windowsill. But the roofs right over their heads can also be fertile ground. The idea of growing plants on the roof, already popular in Northern Europe, is now germinating in U.S. cities.

From meadows of wildflowers to crops of vegetables, gardens are topping buildings from Seattle to Maryland. Today's green roofs are far more sophisticated than the sod huts the Vikings built centuries ago, and ecological soundness is becoming ever more crucial. Colin Cheney, the New York City-based director of Earth Pledge's Green Roofs Initiative (www.earthpledge.org/GreenRoof.html), likens them to the hanging gardens of Babylon in the Mesopotamian desert. "We're trying to create verdant garden patches in the midst of all this cement," says Cheney.

The structure is fairly simple: The entire roof surface is covered with soil, which the urban gardener sows. Beneath the plants, a system of layered components keeps roots from digging into the roof and collects rainwater. There are two different types of green roofs: extensive and intensive. Homeowners work with an engineer or architect to see what type of roof works best for their space and matches their level of commitment. The lower-maintenance extensive roof has a shallow layer of soil, about 2 to 4 inches deep, and is really more of a meadow than a garden. Intensive green roofs are designed for heavy-duty garden use. The soil is 8 to 12 inches deep, so it can host heartier plants and small trees, and it may require fertilizer and irrigation.

Like a lot of eco upgrades, green roofs initially cost more than regular ones. According to Cheney, conventional roofs, depending on the location and other variables, can cost $6 to $15 per square foot. Extensive green roofs, including the soil and plants, cost between $15 and $30 per square foot. "But they're worth it," says Cheney: "A normal roof system lasts 12 to 15 years. The green roof will last twice as long, so it's really an up-front investment that will pay off." Many homeowners are making the investment, knowing that they'll save on future utility bills and that they're doing the environment a kind turn. Susan Boyle and her husband, Benton Brown, did just that when they renovated the icehouse of an old brewery in Brooklyn, N.Y., for a living space. "We intend to use it as a yard one day," Boyle says. "But we're also trying to make the building as sustainable as possible. This will insulate in the winter and help us avoid air-conditioning in the summer."

Green roofs counter the "heat-island effect" that cities with more concrete than organic space suffer: Dark roofs and cement store the sun's heat and raise temperatures. "Plants can transform heat and soil moisture into humidity," explains Halsted Welles, owner of Halsted Welles Associates, Inc., a company that specializes in designing and installing rooftop gardens in New York City. "This is a natural cooling system." Green roofs cool both the building and the surrounding atmosphere. "Imagine how being in a forest feels, versus sitting on a rock in the sun," adds Welles. "That's the difference plants make."

Ed Snodgrass, owner of the 160-year-old family-founded farm and nursery Emory Knoll Farms (www.greenroofplants.com) in Street, Md., also notes the growing trend. Since 1999, his business has supplied plants exclusively for green roofs. Last year he helped create about 200,000 square feet of this country's green roofs; this year he's starting one project that alone equals 400,000 square feet. Snodgrass says more and more industrial buildings are installing green roofs in order to comply with storm-water regulations — and because some cities and municipalities are starting to offer incentives to install them. Individual green-roof enthusiasts have slightly different motivations. "Most people want to participate in ecology firsthand," says Snodgrass. "This way, any homeowner can help with environmental problems. They also create local habitat for birds and butterflies. It's as much for their own pleasure as anything."