When it rains on the Yorktowne Square Condominiums in Falls Church, VA, one of its buildings doesn’t pour as much runoff into local waterways as it did in previous years—nor is there as much of the sediment and nutrient pollution that travels with it.

The reason is a new layer of rooftop greenery.

The roof now sports a living carpet of approximately 8,000 sedums—small, succulent plants that tolerate a wide range of temperatures and drought—on a flat expanse of 4,700 square feet. The Yorktowne “green roof” uses a lightweight design, retrofitted to a conventional rooftop on a 30-year-old residential building.

It recently garnered a 2005 award for North American Green Roofs of Excellence, presented by the nonprofit industry association, Green Roofs for Healthy Cities.

Steven Peck, executive director of the association, said the reasons for Yorktowne’s success reach beyond successful design.

“The project included lots of owner participation and consultation with the community to integrate the green roof with a holistic approach to stormwater management,” Peck said. “Green roofs are not like a coat of paint that you slap on at the end. They provide multiple benefits for the building and the community, and this project did a great job of maximizing those benefits.”

Jeanette Stewart, president of the Yorktowne Condominium Association and director of EcoStewards Alliance, is especially pleased with the roof’s contribution to stormwater management.

“I consider green roofs a wonderful fix for some of our stormwater problems,” she said “There’s very little maintenance, and they do a spectacular job cleaning stormwater and reducing runoff.”

Normally, impervious surfaces such as roads and roofs—especially those built before stormwater regulations were enacted—quickly flush water into local streams, along with any pollution picked up along the way. The rapid rush of water also dramatically alters natural stream hydrology, causing extensive erosion. As a result, urban streams are often the most degraded in a watershed.

Because of its impact on local waterways, and the Chesapeake, finding ways to control stormwater runoff in older developments has been a goal of the Bay Program. Green roofs, which can provide benefits to property owners and water quality, are a stormwater control technique that has been gaining increased interest in recent year.

Monitoring results from the Yorktowne project illustrate why a touch of rooftop green can help. “So far, we’ve seen runoff reductions as high as 70 to 80 percent during a 1-inch rain event,” Stewart said.

Those are normal stormwater reduction figures for green roofs during summer months, according to Green Roofs for Healthy Cities. During the winter, green roofs reduce runoff by approximately 25 to 40 percent.

These reductions can be achieved through either deeper plantings, designed as rooftop gardens with public access and additional structural support, or relatively shallow plant beds designed for minimal human traffic that add little or no additional weight to the roof.

“With green roofs, people usually think of trees and a lot of weight,” Stewart said. “But many green roofs aren’t any heavier than a conventional roof.”

In the residential setting of Yorktowne Condominiums, planners hired a structural engineer to determine the weight-bearing capacity of the roof. “We found that we could max out at 15 pounds per square feet of dead load,” Stewart said.

Then, as the Yorktowne work crew prepared for the green roof by removing and replacing the old sheathing, they found a surprise.

“Lo and behold there was a second, older roof underneath it,” he said. “We had no idea. We’d been over the weight capacity for years.”

The new lightweight green roof corrects those issues. It also provides protective covering for roofing materials, extending the life of the roof by two or three times that of a conventional roof.

Durability is one of the direct ways that owners recoup installation costs, which often run between $12 and $24 per square foot. The Yorktowne green roof is expected to last approximately 40 years.

“It’s under warranty, like any roof,” Stewart said. “But we are handling all of the maintenance ourselves, because there’s so little of it. We weed once a year, but there’s not much to pull. And as it fills up with sedum, there’s less and less. We also keep the drains clean, but there’s no maintenance other than that. I’ve never fertilized the roof, or irrigated it.”

The Yorktowne green roof is also helping to heat and cool the building, which reduces energy costs. Rooms under a green roof are significantly cooler than those under conventional roofs during the summer. This is a big benefit for property owners in urban areas where summer temperatures—and cooling costs—skyrocket.

Collectively, green roofs help to offset the urban “heat island” effect in cities, where paved and reflective surfaces absorb and radiate heat. Urban green roofs also soften street noise and provide green retreats that are often considered safer than their street-level counterparts.

“Green roofs are truly outstanding in terms of the scale and scope of the benefits that are possible,” Peck said. “And those benefits really do meet pressing needs in our communities, like the need to preserve our waterbodies, the need for cool cities that we can live in in the summer and the need for enhanced green space.”

Green roofs are also sprouting in rural locations, often driven by residential and commercial property owners interested in environmental stewardship.

The Life Expressions Wellness Center, nestled in a mountain valley of central Pennsylvania, is another example of rural green roof architecture in the Chesapeake watershed. It received a Green Roofs of Excellence Award in 2004. This green roof was designed for an unusually steep pitch, with great sensitivity to the aesthetics of the entire building. The result is a carpet of plants on a uniquely arched rooftop that echoes the curves of its mountain valley skyline.

“The shape and structure reflect the philosophy of the owners,” said Charlie Miller, of Roofscapes Inc., which designed the green roof. “Their primary interest was in having the building be alive, efficient and sustainable.”

Rainwater drains along the full length of the eaves, dripping from tendrils of overhanging plants and creating a “curtain effect” during rainfalls. This enhances the roof’s ability to reduce runoff by prolonging the duration of runoff that occurs.

Green roofs are gaining momentum across the nation, especially in Portland, OR, and Chicago. In the Chesapeake Bay watershed, the District of Columbia is the center of green roof activity, where at least 200,000 square feet of the roofs are slated for installation in the next two years.

Emory Knoll Farms, a leading supplier of green roof plants for the East Coast, bears witness to this increased activity. Co-owner John Shepley reported that business has doubled in the last three years, and he expects it to double again next year, without advertising. The average size of the projects is also increasing, and most of them are in the Bay watershed.

Green roof coverage lags far behind European communities, where green roofs have been a vital urban planning tool for decades.

Germany, in particular, is a leader in green roof design and installation. According Penn State University researchers, German roofing companies installed nearly 350 million square feet of green roofs between 1989 and 1999 alone, and the rate has continued to increase.

Green roofs flourish in Germany and other European countries because governments recognize the public benefits and provide both legislative and financial support for their installation.

In the Chesapeake watershed, demonstration sites and incentive programs are boosting the presence of green roofs, especially in urban settings and locations that serve as demonstration sites.

The Yorktowne Condominium association, for example, offset costs with $80,000 in combined grant funding from Chesapeake Bay Program sources, including the Virginia Department of Conservation and Natural Resources and the National Fish and Wildlife Foundation Small Watershed Grants Program.

In Richmond, VA, the SunTrust Mid-Atlantic Bank received $28,000 from the Alliance for the Chesapeake Bay to help create the largest completed green roof in Virginia. SunTrust installed a 12,000-square-foot green roof at their company headquarters in a high-visibility location near the James River.

Stacey Moulds, senior program coordinator for the Alliance, said that public demonstration elements were critical in the selection process because the only existing green roof in the Richmond area is on a private residence.

“Ultimately, SunTrust won the grant because of the high amount of square footage, and because it is such a well-known entity, close to the river and in a prominent location,” Moulds said.

Kevin Kolda, vice president of SunTrust facilities management, said that the company had been evaluating green roof options when the Alliance grant program was announced.

“The grant program was the deciding factor, making the green roof possible from a financial standpoint,” he said. “I felt that this was an ideal opportunity for SunTrust to tie in our roof replacement with something good for the environment. Hopefully, it will inspire others to do the same in the future.”

Moulds said that SunTrust’s example is doing just that. The project was completed in August and has already generated several calls to the Alliance from individuals and corporations interested in green roofs.

The SunTrust green roof will be completed in September, celebrated with a ribbon-cutting, signs, a viewing platform and a series of public tours.

In the District of Columbia, the Chesapeake Bay Foundation has provided more than $300,000 for nine projects that will add more than 100,000 square feet of green roofs to the city.

Doug Siglin, who manages the CBF’s green roof grant program, said the program targets commercial properties because stormwater issues are so urgent, and commercial rooftops provide the greatest amount of space to work with.

“There isn’t a whole lot you can do in a built-out city to manage stormwater, because so much of the land is covered by rooftops,” Siglin said. “You can’t do ponds and other techniques used in suburban areas. One of most powerful techniques that you can do is green roofs.”

Green roofs are especially important for areas like the District of Columbia, which use a “combined” sewage system to carry both human waste and surface runoff through one set of pipes. Because the system was built for an earlier era, it often can’t handle the surge from storm events. The system overflows and carries everything directly into the river. Green roofs prevent overflows by keeping a lot of water from entering the outdated sewer system.

To encourage coverage in the Anacostia watershed, the CBF has provided commercial property owners with 20 percent of the cost difference between a green roof and a conventional roof.

“We felt that 20 percent was enough to attract people, with the owner still putting in 80 percent of the cost toward achieving a public goal,” Siglin said.

Their signature project will cover 68,000 square feet atop the new building that will house the federal Department of Transportation and may be the largest green roof on the East Coast.

Nevertheless, Siglin said, “Scale matters. It’s a great step forward, but it still won’t save the river. We’d need a lot more coverage than we have now.”

Many green roof advocates would like to see governments at all levels provide support that is more in line with their European counterparts.

“The next frontier is to mainstream this stuff,” Siglin said. “The states could encourage these things more than they do right now. They won’t stand in your way, but that’s different from actively encouraging it.”

Charlie Miller, of Roofscapes Inc., made similar observations about the green roof project he designed for the Life Expressions Wellness Center.

“The township was aware of all of the environmental and energy benefits, but didn’t give them any credit for the fact that their roof sheds very little rainwater. They still had to build a retention area,” Miller said. “It’s really a frustration that current regulations don’t recognize the benefits and give people the credit they deserve.”

Even at the community level, there is work to be done. People who will live or work under green roofs often need informed introductions that put them at ease with the concept.

At Yorktowne Condominiums, Jeanette Stewart said that, in retrospect, she would put more emphasis on outreach and education. The green roof was helped along by a progressive board of directors, but there were still concerns to allay about structural soundness. And there were no local examples of green roofs available.

“A lot of people are afraid of stepping out and taking a risk,” Stewart said, “but with the track record of green roofs in Europe, I didn’t feel like I was going out on a limb.”

The Richmond office of the Alliance for the Chesapeake Bay will be conducting tours of the SunTrust Mid-Atlantic Bank’s green roof Sept. 13-16. Group tours after this period will be available upon request. For information, contact Stacey Moulds at mailto:smoulds@acb-online.org or 804-775-0951 or visit www.acb-online.org/project.cfm.