Green roofs popping up in big cities

Most green roofs still feature sedum and ice plant succulents, which can tolerate harsh growing conditions and are ideally suited for low-maintenance rooftops. These “extensive” roofs, as they’re known, require only a few inches of growing medium, reducing overall weight and cost.

John Shepley, co-owner of Maryland’s Emory Knoll Farms with industry leader Ed Snodgrass, said business is booming at their green roof plant nursery, based on a former dairy farm. “We’re probably growing 50 percent annually without trying,” Shepley said. Although Washington, D.C., and New York City remain big markets,  he said, the federal government has been coming on strong with new mandates for green buildings.

In mid-March, Shepley delivered pregrown sedum plugs to cover a concessions area at the new Washington Nationals baseball stadium. Two years ago, the business helped install thousands more grass plugs on a massive green roof for a Library of Congress facility in Culpepper, Va.

As green roof technology matures, new projects have begun unveiling increasingly varied designs, including “intensive” roofs that require deeper growing depths and considerably more investment but can deliver more aesthetic, conservation and other benefits. Chicago’s $480 million Millennium Park, a 24.5-acre cap over rail yards and a parking garage, is one of the world’s largest intensive green roofs to date. An award winner from Green Roofs for Healthy Cities, the project has all the advantages of a major urban park, Peck maintains.

Photo courtesy of Green Roofs for Healthy Cities Ford’s Dearborn, Mich., Truck Assembly Plant features one of the largest green roofs in the eastern United States, an award-winning system that covers an area of about 10.4 acres with nine varieties of hardy Sedum grass.

Considered the industry frontrunner among North American cities, Chicago used a mix of intensive and extensive vegetation to cover 20,000 square feet atop its City Hall in 2001. In August of that year, researchers recorded a rooftop temperature of 119 degrees in the planted area, compared with a blistering 169 degrees on an adjoining black tar roof. Since then, the green roof has saved the city an estimated $3,600 in annual cooling and heating costs. If all Chicago roofs were similarly clad, city officials believe peak energy demand could be cut by 720 megawatts, or enough electricity for 750,000 consumers. Similarly, the load on the city’s storm sewer system could be slashed by roughly 70 percent.

Chicago is now adding green roofs to everything from office buildings to fire stations, and city governments in Toronto, Minneapolis and Seattle are following suit.

Other city-based incentives, popular in Chicago and Portland, give developers extra floor space if they add green roofs, and fast-track programs are rewarding environmentally conscious projects with a front-of-the-line approval process.

Washington, D.C., which has long struggled to control storm-water overflows into the Potomac and Anacostia Rivers, is moving toward a system that will account for impervious building surfaces that increase runoff when assessing water consumption fees. Adding more water-retaining surfaces, including green roofs, will effectively lower a building owner's city fees. Beyond relieving the impact of development, the measure is designed to encourage both public and private-sector investment into runoff-reduction technology.

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