Also, this year, more green roof square footage was installed on public projects vs. private projects, whereas in previous years this has been more equal.

"We are pleased to see the continued expansion of the green roof market," points out Steven Peck, GRHC founder and president. "The industry's continued growth is fueled by the multiple public and private benefits green roofs bring, such as stormwater management, reducing the urban heat island, energy savings and green jobs."

The Washington, D.C., metropolitan region saw the installation of 2,164,926 sq. ft. of green roofs in 2013—the highest among all the other regions, far surpassing the next four metropolitan regions on the list: Chicago, New York, Philadelphia and Boston, respectively.

Washington has adopted public policies and programs that support green roof investment, including rebates of $7 to $15 per square foot of green roof installed and credits that reduce stormwater fees.

"The fact that the District once again leads the nation in installation of green roofs is another example of how our government, private organizations and individual residents are working together to ensure that we are the most sustainable city in the nation," says Mayor Vincent C. Gray. "Green roofs are part of the solution for capturing stormwater and cleaning up our local rivers, and I am proud of the work of everyone who has helped us achieve this honor once again."

"With supportive public policies like those in Washington, D.C.," Peck adds, "we will make progress toward achieving the industry goal of 1 billion square feet of green roofs installed by 2022."