Photo credit: Clark Construction

The Department of Homeland Security is consolidating its headquarters to a new complex in southeast Washington, D.C. In addition to being more efficient for logistical reasons, the 40-building campus is likely to be one of the most sustainable in the nation.

Deliberate measures are being taken for both new and renovated buildings to meet government mandates on building operation and LEED energy requirements. Phase 1 of the project, to be delivered in 2013, includes a new U. S. Coast Guard Headquarters complete with 400,000 square feet of green roofing.

Built into a hillside, the Coast Guard project includes an 11-story office building which will provide 1.2 million square feet for 3,860 employees, a separate central utility plant and two seven-story parking garages. Incorporating a green roof for all 20 structures helps to maintain more of the site’s natural contour, as well as conserving energy and reducing storm water runoff.

Coast-Guard-Green-RoofPhoto credit: Clark Construction

Covering hundreds of thousands of square feet of federal rooftop with living plants is no DIY weekend task. Construction and design teams were challenged to find plants that could withstand the hot, sticky D.C. summers without requiring a massive amount of water. The DHS consulted with Ed Snodgrass of Emory Knoll Farms and HOK Inc. to select plants that could be grown and supplied to such an extensive roof. Ultimately, the group decided on variety of plants ranging from shrubs to grasses, as well as pre-vegetated sedum mats from Sempergreen.

To prepare the rooftops for planting, construction crews first applied a waterproof layer of hot rubberized asphalt. They then installed a customized drip irrigation system that utilizes gray water from an on-site stormwater wet pond to provide long-term hydration for the plants. An overhead sprinkler system was also installed, but will only be used temporarily to provide while the plants are taking root. It will later be removed because it uses potable water and violates the LEED standards for irrigation. Lastly, soil was hoisted by crane or pneumatically conveyed and blown on the roof.

Once complete, the green roof will not only look great, but also retain storm water that would otherwise combine with waste water that may bypass the Blue Plains Wastewater Treatment Plant, just downstream from the site.