A large green roof in Washington, D.C., and one of the largest on the East Coast is on the new headquarters building for the U.S. Department of Transportation (DOT).
Installing a green roof on the building is part of a current movement in Washington, D.C., says Paul Elias, managing director for The JBG Cos., Chevy Chase, Md., the company that owns the building.
"The southeast Washington area is going through revitalization," Elias says. "We believed the green roof would set a good example and be good for the area."
Gordon Contractors Inc., Capitol Heights, Md., was asked to perform the green roof system installation, including roof membranes and waterproofing for the project. With previous experience, the company was prepared.
"We've been installing green roofs for a long time, but they weren't called green roofs back then—they used to be called courtyards," says Steve Wilt, vice president of Gordon Contractors. "Before this project, we probably had installed about 10 'green roofs.'"
One of the main reasons The JBG Cos. chose a green roof system for the new building was for stormwater management.
"Because of the building's size, we would have had to put sand filters around the site for stormwater management, which would have been difficult," Elias says. "So we chose a green roof instead."
The roof system is 160,000 square feet of which 69,000 square feet is a green roof system.
Gordon Contractors installed an American PermaQuik roof system consisting of 215-mil-thick PQ 6100—a hot fluid-applied rubberized asphalt roof system—on all roof areas. A PermaFlex 30 protection layer was installed on the nongreen roof area, and PQ 2171 Root Barrier was installed on the green roof area.
Dow Plazamate insulation was installed on all roof areas, and the green roof area received PQ 7609 composite filter fabric, PQ 7610 reservoir board and PQ 7611 moisture-retention mat.
Finally, Gordon Contractors installed 3-inch-thick engineered soil and sedums on the green roof area; 12-foot-wide, 2-inch-thick precast concrete paver border at the roof perimeter; and stone ballast on the remaining roof areas.
With regard to safety, the company used stanchions and safety cables mounted on concrete davit curbs.
The company used a 70-ton crane to hoist all the materials 138 feet.
"The most challenging aspect of the project was the amount of product that had to be hoisted to the roof," Wilt says. "We used cranes to hoist all the materials, and for safety reasons, there were concrete bollards installed around the building to keep vehicles back. But this limited the crane's access to the building, which meant we had to use more manpower to move material around the various roof areas. We had to hoist soil, as well as concrete roof pavers that were installed around the perimeter of the roof."
The JBG Cos. was happy with the results of the green roof installation.
"It looks great," Elias says. "Everything's planted, and now we just have to see how it functions."
The JBG Cos. often works with the Chesapeake Bay Foundation and is part of the foundation's Green Roof Incentive Grant Program, which, according to the foundation's Web site, www.cbf.org, exists to create green roofs that will benefit the water quality of the Chesapeake Bay and Anacostia River.
"We're going to continue to work with the Chesapeake Bay Foundation to see how green roof systems are functioning," Elias says.
Wilt also is satisfied with the green roof installation and its potential benefits.
"It was rewarding to install a high-end green roof system that will help with the city's stormwater management," Wilt says. "Also, there will be significant prestige associated with this structure because it will be occupied by DOT."
Krista Reisdorf is managing editor of Professional Roofing magazine
Project name: U.S. Department of Transportation Headquarters
Project location: Washington, D.C.
Project duration: March 2006-September 2006
Roof system type: Green roof
Roofing contractor: Gordon Contractors Inc., Capitol Heights, Md.
Roofing manufacturer: American PermaQuik, Williamsville, N.Y.