September 1, 2006
Green-roof technology now offers a host of options—from the humble patch of grass to sophisticated feats of structural engineering.
FOX RESIDENCE: Chicago: Box Design
As green-roof technology improves, the front yard—that symbol of sprawl and plentitude—may be poised to move from the suburbs to a more energy-efficient spot atop inner-city buildings. Recently, Chicago designer Kevin Fox added a lawn to the roof of the two-story building he occupies near the Sears Tower.
Fox made the $60,000 investment because his supplier, American Hydrotech, warranted a special plastic to keep the water that feeds the grass from dripping into his living space. “You coat the deck with the membrane using a squeegee,” landscaper Kurt Horvath says. “It’s so hot that it touches the other membrane that was laid down beforehand and fuses to become one solid membrane.”
To deal with the increased load, Fox refitted the roof with steel joists and decking that supports the required seven to ten inches of soil. While grass is not an ideal plant for green roofs, it can still provide environmental and economic benefits. “Upkeep?” he says. “I mow the lawn here among all the high-rises. People look out their window and get a giggle out of it.” —Alec Appelbaum
ASLA HEADQUARTERS: Washington, D.C.: Michael Van Valkenburgh Associates
When the American Society of Landscape Architects decided to build a green roof on its Washington, D.C., headquarters, Michael Van Valkenburgh immediately understood the implications. “If ASLA was going to hire a landscaper,” he says, “the reason would be to show publicly that it could be an operating garden.”
For the 3,300-square-foot roof of the Chinatown building, Michael Van Valkenburgh Associates (MVVA) extruded the elevator shaft to support multiple layers of insulation filler, preexisting mechanicals, a wood deck, and steel grating for visitors to provide cover for some plants. Then the firm created two “waves” with 4.5-inch and 6.5-inch soil slopes to maximize visibility from the street. Since public outreach was a priority, MVVA designed a dramatic stairway that opens to a shelter with a skylight.
Van Valkenburgh hopes the project provides a useful case study: “We tried a regional pattern with more than twenty species to see what would do well up there.” Sadly the project’s $900,000 budget didn’t allow ADA-accessible ramps amid the rooftop mechanicals. “Much of the roofscapes of cities are made of smaller roofs that are difficult to retrofit,” he says. The firm is now tackling a similar challenge at the Boston Architectural College. —A.A.
MASS GENERAL HOSPITAL: Boston: Cambridge Seven Associates and Halvorson Design Partnership
Like most health-care institutions, Massachusetts General Hospital serves its patients first. But in planting a 6,500-square-foot healing garden on top of its Yawkey Center—a new outpatient facility designed by Cambridge Seven Associates—the hospital was able to give cancer patients a long sought-after amenity and conserve energy in the process.
Rob Adams of Halvorson Design Partnership, the roof’s landscape architects, says the healing garden offers all the benefits of a green roof without the science-experiment gadgetry typical of many projects. The firm instead concentrated on the patient experience, setting teak benches in clusters around mostly native perennials like paperbark maple, river birch, and blueberry. The environmental benefits have largely taken care of themselves. With a soil depth of eight to 36 inches, the roof is four times more efficient as insulation than a conventional roof and has attracted a range of butterflies and birds. —Michael Silverberg
ROOFTOP FARMS: Liuzhou, China: William McDonough + Partners
William McDonough has been at the forefront of green roofs for almost a decade now. Recently his firm unveiled a conceptual proposal to bring rooftop farms
to Chinese cities that are losing cropland at an alarming rate.
For example, the city of Liuzhou—a former agricultural center in southern China with an oxbow river on its border and a surging population—is rapidly running out of places to plant soybeans and sugarcane.
With help from the China-US Center for Sustainable Development, McDonough has envisioned a series of buildings with bridges connecting soil-bed roofs. German green-roof manufacturer Xeroflor will analyze how much weight in tree roots and rice-paddy water the roofs can handle.
“The premier of China has said that if the country continues its current pace it will lose twenty-five percent of its farmland by 2020,” McDonough says. “The current urbanization puts pressure on the good farmland, which is around the cities—and that pressure will then transfer itself to the perimeter, where the marginal lands are. Those lands are typically the last reserves of the natural world.” —A.A.
CALIFORNIA ACADEMY OF SCIENCES: San Francisco: Renzo Piano Building Workshop
Renzo Piano’s design for the California Academy of Sciences, in San Francisco, possesses a stunning gesture of apparent simplicity: the 370,000-square-foot building features a rolling 2.5-acre “living roof” that—after completion next year—will stitch the structure back into its bucolic Golden Gate Park site. Centerpiece to a comprehensive environmental effort that the academy hopes will merit a LEED Platinum rating, the living roof is an intense feat of structural engineering and horticultural know-how.
“We’ve got slopes up to sixty degrees on these hills,” says Jean Rogers, an environmental engineer with Arup’s San Francisco office. “Trying to keep the structural integrity of that soil bed—which is about a foot thick—while punctuating the roof with skylights was a challenge.” The structural steel system supports a drainage layer, a filter sheet, a growing medium, and up to 1.7 million native California plants. Prior to construction, a full-scale roof mock- up was built in Hayward.
Plant selection has been equally rigorous. A team of landscape specialists and the academy’s in-house botanists tested 36 native California plant species, and ultimately selected a total of eight. “Before we moved, we tested a variety of species on the roof of the old building,” says Frank Almeda, a senior curator at the academy’s botany department. The living roof is currently being grown off-site, in Marin County. —Martin C. Pedersen