Visitors to the U.S. Coast Guard headquarters won’t see the ocean blue but can enjoy a sea of green across the rooftops.
One of the Federally mandated sustainability requirements for the 11-level, 1.2 million square foot headquarters located in Washington D.C. was a 300,000-plus square-foot Vegetative Roof Assembly (VRA). The project is the second largest green roof in the nation.
Because the U.S. Coast Guard Headquarters structure is terraced into the hillside with elevation changes of 120 feet, two levels were above ground while the remaining nine were built into the hillside. Given the unique lay of the land, architectural design and construction team navigated a range of design considerations to ultimately receive LEED Gold certification from the U.S. Green Building Council.
A cross-functional team collaborated throughout the three-phased VRA construction. Under the direction of WDG Architecture, the architect of record for the roofing, and HOK, the lead for vegetative roof components, Gordon Contracting served as the roofing contractor and Tilson Group supplied and installed the hundreds of thousands of individual vegetative roof plants.
The designers said the system reflects five local eco-regions, from the Piedmont uplands down to the coastal plain. The project included more than 200,000 plants, 300 native trees, and about 100 varieties of sedum. One courtyard even features a “dry river bed” that mimics the bends of the Potomac as it winds toward Washington from the Chesapeake Bay.
From the outset of the project, the integrated roofing team was tasked with designing a VRA that would help decrease the building’s heating and cooling energy usage, reduce and filter stormwater runoff, lower long-term maintenance and extend the life of the roof. The unique roof would also serve to integrate the 176-acre campus with the building and its 4,000 occupants.
Given the sheer scope and size of the VRA project, the team had to make some adjustments. The team adjusted the engineered soil specification to reduce the loads within the structural tolerances for the roof structure and carefully addressed a range of pH, moisture, organic matter and nutrient levels to support the variety of plants.
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