• Credit: Brent Bingham dba Foto Fx 

Green roofs may only represent a very small part of the total U.S. residential market, but the industry still saw triple-digit growth last year.

“The green roof industry grew by 115 percent over the course of 2011, up significantly from 28.5 percent growth recorded in 2010,” says Steven W. Peck, president of Green Roofs for Healthy Cities (GRHC), an association that promotes the development of green roofs and walls in North America.

The association has a theory for the strong growth over the last year. “We are definitely beginning to see results from policy support that has increased over the past few years,” says Jeffrey L. Bruce, chair of GRHC. “The industry is also benefiting from the more than 500 accredited green roof professionals (GRPs) in the market, who are committed to driving future industry growth.”

At the same time the group released it numbers, it announced that Washington, D.C., for the first time jumped to top of the metro rankings with more than 800,000 square feet of green roofs installed in 2011. Washington, D.C., Mayor Vincent C. Gray says it shows that the city’s aggressive adoption of green infrastructure continues to pay off.

“This is evidence that the District is moving toward my vision for a sustainable D.C. and will lead the nation in implementing green practices and growing a green economy,” the D.C. mayor says. “We are fully committed to being No. 1 again next year.”

Chicago is still the green roof leader among metro areas over the past decade, the association adds. “With a total of over five million square feet of installed green roofs, it is one million square feet ahead of any other metro region since the survey started in 2004,” the GRHC says.

A green roof is one that consists of several layers of protected membranes and soil medium, and planted with any type of vegetation, including succulents, grasses, and other plants. Green roof advocates say the system offers a tremendous amount of benefits, including increased insulation for the building, added energy efficiency, and stormwater management.

In urban applications, green roofs help clean the air, reduce the stress off sewer systems through stormwater retention, and help reduce the heat island effect that makes urban temperatures climb in the summer.

Paul Erlichman, membership coordinator for the association, says the institutional sector of the market saw the biggest green roof gains, but he says commercial, multi-unit residential, industrial, and single-family residential also saw strong growth. “This is based on total square footage, and institutional projects tend to be largest,” he adds.

Green roofs are ideal on commercial, institutional, and civic buildings that are flat, but they can also be installed on low-sloped houses. Erlichman estimates that residential installations make up about 20 percent of the green roof market and offers a theory how the technology can grow in the single-family market.

“As awareness grows on the multiple benefits of green roofs and the success of the industry, more homeowners will recognize green roofs as investments that will pay financial and environmental dividends,” he says. “At a larger scale, an increasing amount of policies such as Toronto's Green Roof Bylaw will require that developers use green infrastructure principles in their projects. Certainly, the further development of these policies will make our cities greener and drive the residential green roof market.”

Nigel F. Maynard is a senior editor for Builder magazine.