When DC Mayor Vincent Gray said his city boasts the most square footage of green roofs in the nation, he was almost right.

The District installed more green roofs in 2012 than any other city in North America, according to an industry survey by Green Roofs for Healthy Cities. But the city trails Chicago in the competition for the most green rooftop real estate.

That said, the District’s leadership in the field of green roofs — also known as living, vegetated or eco roofs — is nothing to scoff at. Green roofs include alternative surfaces like growing media that support plant life and help store and filter stormwater, thus reducing pollution to local waterways.

Federal and local players in the District, which is situated at the confluence of the Potomac and Anacostia rivers, have embraced green roofs as one of many measures to reduce polluted stormwater runoff to the Chesapeake Bay. Their growth here can be linked in part to Gray’s Sustainable DC initiative, launched in 2011 to make the city the “greenest, healthiest and most livable” in the nation over the next 20 years.

Included in his plan is a goal to make all of the District’s waterways swimmable and fishable by 2032 and to use 75 percent of the city’s landscape to capture rainwater for filtration or reuse.

Green roofs, which have gained popularity over the last five years, have begun to take root in this city as developers adapt to meet new environmental standards and more residents come to embrace the technology.

In other regions of the watershed, green roofs are still at more of an early adapter stage. They are promoted by Bay organizations as a way to improve the environment, conserve energy and even save money in the long run. But few areas offer the incentives that the District does to residents and businesses interested in implementation.

Also to the District’s advantage is the fact that, when a federal building adds a green roof, it’s usually big. The city’s 2012 numbers got a boost from the construction of a new, 1.2-million-square-foot U.S. Coast Guard Headquarters near the Anacostia, which features so much green roofing it almost looks like a golf course from above.

The U.S. General Services Administration alone maintains more than 45 football fields’ worth of green roofs on federal buildings in the city. And the District government and its residents have been pulling their weight on green roofs as well.

Rebecca Stack, a Low Impact Development specialist with the District Department of the Environment, said a number of factors have converged to make DC a leader on green roof turf.

She said the total number of green roofs is dispersed somewhat evenly among federal, commercial, municipal and residential buildings in the city, though some sectors see more growth in a given year. The District has been installing and recognizing the benefits of green roofs since about 2004.

The Chesapeake Bay Foundation began building green roof demonstration projects in the District in 2003 as part of a consent decree settlement with the DC Water and Sewer Authority. The CBF issued grants for the installation and maintenance of eight demonstration roofs in the Anacostia watershed to show that such projects were feasible and economical for commercial buildings in the city.

But how did the nation’s capital grow its green roof portfolio faster than some of the nation’s greenest cities? Stack says cities like Portland, OR, have about the same number of green roofs as DC does but took a different approach in implementing them.

Portland, for example, has added a great number of small green roofs that were mostly driven by residential demand. While several DC residents have added green roofs of their own volition, many more green roofs have been installed to meet requirements to help the federal government — which owns about a third of rooftop area in the city — reduce its stormwater footprint.

The Energy Independence and Security Act of 2007, for example, demands that any new federal construction meet stringent stormwater standards. Green roofs quickly became one of the easiest retrofits and additions to new buildings to help developers meet these requirements.

“People have been using green roofs to meet regulatory obligations,” Stack said. “And the District has had stormwater regulations since 1987.”

Private developers in the city have also made commitments to reducing stormwater runoff, in part because they can’t lease space to the federal government unless they are compliant with certain green building measures.

Along with these factors, perhaps the biggest driver for the District and nearby municipalities to embrace innovative stormwater solutions is the pressing need to do so. The CBF released a report in January urging municipalities and legislators to do more to address stormwater runoff, the only major source of pollution to the Bay that continues to grow.

“I think the Chesapeake Bay is a good incubator for innovation in stormwater,” Stack said. “The fact that there are problems clearly linked to stormwater runoff has helped to make the region one of the important places for it.”

Maryland’s Prince George’s County also has proven a leader in stormwater innovation. Rain gardens to absorb excess water with plants and bioretention ponds to foster water filtration were first floated there, Stack said.

Since 2007, DC residents also have had a financial incentive to consider green roofs. The District began that year offering residents $3 per square foot for implementing green roofs, an incentive that has since grown to $7 per square foot. Residents within the Anacostia watershed can now receive $10 per square foot.

Prince George’s County is following suit, and is beginning to offer a similar incentives program. When the District first launched the program, only New York City offered an incentive for green roofs but in the form of a tax credit, Stack said.

Michael Lucy, who administers the District’s green roof rebate program through the Anacostia Watershed Society, says participants in the program quickly become ambassadors for it to their neighbors and friends.

“People install green roofs because they’re wonderful,” Lucy said. “They want their building to be more environmentally responsible and integrated with the great outdoors. They want to manage stormwater or they love the look and want to provide more habitat.”

Graeme King, who lives in D.C.’s Petworth neighborhood, said he first stumbled across green roofs in a library book. He and his wife had already invested time in raised garden beds and rain barrels, so they gave green roofs a closer look. “I thought it was a cool idea to turn dead space into something living,” he said.

The Kings ended up contracting with DC Greenworks to install the roof and help with its permitting and rebating. The couple remained involved in its installation and design, which included landscaping the roof to look like the confluence of the Anacostia and Potomac rivers from above, with branches of gravel pathways that mimic the shapes of the rivers snaking through its center.

Like most green roofs, theirs was planted with a mix of plants that grow in shallow soil and require little maintenance. The roof provides additional habitat for birds and insects, including bees that live in a beehive on the roof.

King said the 300-square-foot roof cost them about $10,000 before they received a rebate from the District. He says it has added value to the house, extended the life of their roof and provided a pretty second-floor view for their neighbors.

Susan Benesch, who lives near DC’s Logan Circle, said she was able to save money by installing a green roof herself — one that now grows food as well as stormwater-retaining plants.

Installed in August, Benesch’s rooftop garden flourished with blueberry and raspberry bushes, lettuce, kale and radishes as well as herbs like lavender and rosemary. She installed cedar planters that provided space for more gardening on three sides of the roof.

She dug into library books for the project and enlisted the help of others. At one point, a master’s student in urban ecology used the roof to test her hypothesis that vegetables grown on a roof are purer than those grown on the ground in a city.

Benesch grew up with a green roof of sorts in the Bronx of New York and has loved implementing her own creative version in DC.

“I have been renovating my house since I bought it three years ago, in as ‘green’ and sustainable way as I can,” Benesch wrote in an e-mail. “It has been such an amazing experience to create a new sunny, breezy green space up there.”

Residents interested in learning more about the city’s rebate program can visit the green roofs page at Anacostiaws.org. To see a green roof in action, visit the American Society of Landscape Architects in DC, which offers in-person or online tours of its rooftop gardens.