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All-Aboard the Greenroof Ship at the U.S. Coast Guard Headquarters
By Todd Skopic
Northeast Regional Building Science Specialist
All Photos and Graphics Courtesy of Todd Skopic Unless Otherwise Noted
Greenroofs are sprouting up all over the United States and this 400,000 square foot government complex in Washington, DC, is a prime example.
|The partially completed U. S. Coast Guard Headquarters at|
DHS St. Elizabeths Campus.
In an effort to provide a more unified, secure campus that brings together its executive leadership and operational management, the Department of Homeland Security (DHS) is consolidating its headquarters in the National Capital Region at St. Elizabeths Campus. Formerly a government-run hospital for the insane, the St. Elizabeths Hospital site is a National Historic Landmark. Located in the Anacostia neighborhood of southeast Washington, DC, the new complex will unite more than 40 buildings spread out within the area.
Phase 1 is scheduled to deliver in 2013, Phase 2 in 2014, and Phase 3 has a projected completion date of Q4 2016.
The DHS St. Elizabeths campus will utilize various sustainable design measures to reduce its environmental impacts and long term operating costs. These measures meet or exceed government mandates on building operation and LEED energy requirements:
• Majority of buildings are pursuing LEED® 2009 Gold certification
• The site is located near public transportation and has been designed as a pedestrian and shuttle campus reducing vehicular traffic
• Majority of existing structures designed for reuse reducing the new construction footprint
• Concrete material from demolished structures was crushed and recycled for use as site access road material
• Onsite utility cogeneration plant Sustainability in Design
• Onsite storm water runoff will be reduced by 47% through the use of multiple infiltration pits and a staggered release system as not to overwhelm existing utilities
• Several native trees located in construction areas were relocated to holding areas to be replanted after construction
• Use of recycled and regional building materials was specified where available
• Strict recycling guidelines have been established for all construction debris
• Reduction in heat island effect by use of underground parking
The United States Coast Guard Headquarters is the first project at the new DHS St. Elizabeths Campus. While the U.S. Coast Guard is one of the five armed forces of the United States, it is the only military organization within the Department of Homeland Security.
Currently under construction, the Phase 1 U. S. Coast Guard Headquarters will feature several construction and operating measures in accordance with its proposed LEED v2.2 Gold certification, including:
• Over 400,000 square feet of green roof used for storm water management and energy efficiency
• Storm water management system including wet ponds, bio-swales and step pools to handle storm water runoff for entire campus
• Enhanced commissioning of all building systems for maximum efficiency
• Use of green housekeeping measures after completion and occupancy
• Use of low-emitting construction materials and furnishings
In all, 18 roofs and two parking garages will be covered with living roofs.
|DHS St. Elizabeths Campus living rooftops. Graphic by Perkins + Will.|
Source: Clark Construction.
Clark Construction is leading the design/build effort in conjunction with Perkins + Will designing the buildings, WDG Architecture as the architect of record for the roofing, and HOK for the vegetative components on the roof. The 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 2 seven-story parking garages. The whole project is built into a hillside and the elevation changes 120 feet on the 176 acre site. The project is targeting a LEED Gold certification.
The waterproofing/roofing system is 215 mils of the Henry Companies, 790-11, hot rubberized asphalt. According to William Pegues of WDG, “Hot rubberized asphalt is our preferred roofing membrane; it is a tried and true system that we did not have to think twice about.”
The original spec for the Vegetative Roof Assemblies® (VRA) included a single-source warranty by the primary waterproofing/roofing manufacturer. The project team decided to have the primary waterproofing/roofing manufacturer be responsible for the waterproofing system, and the roofing contractor be responsible for the vegetative components.
|Waterproofing one of the Vegetative Roof Assemblies®.|
Gordon Contracting of Capitol Heights, MD is roofing contractor on the project. In the picture above, Gordon’s crew is installing the hot rubberized asphalt. Gordon Contracting has experience in self-performing the installation of the vegetative components on several other large projects, but on this project, they sub-contracted the supply and installation of the vegetative roof plants to the Tilson Group of Vienna, VA.
The VRAs are being constructed in three phases - the first phase began in January, 2010 and was completed in late fall of 2011. The U.S. Coast Guard project is well underway - roofs 1 through 5 are done, starting from the lowest point of the site.
Due to the variety of plants ranging from shrubs to grasses to Sedum mats, there are four different soil blends on the project. The growing media or “engineered soil” specification was adjusted in order to reduce the loads to within the structural tolerances for the roof structure.
Roofmeadow® provided assistance in modifying the specification. While maintaining the intent of the design to support plants that demand a range of pH, moisture, organic matter and nutrient levels, Roofmeadow® influenced the specification in order to conform with materials and methods familiar to the green roof industry.
Rooflite® growing media was specified. To date, approximately 2,000 yards of growing media have been installed already, yet the project will take some 10,000 yards of various rooflite® blends by the time it's done next year.
|Crews working with the rooflite® growing media;|
photo courtesy of rooflite®.
Most of the growing media is being hoisted by crane. Due to some of Gordon’s own crane schedule conflicts, the media was pneumatically conveyed and blown on the roof for the first phase, as show below:
|Spraying the rooflite® growing media|
atop the new U.S. Coast Guard HQ.
The plants themselves provided two separate challenges. First, due to the large areas that need to be covered, it is difficult to complete the installation due to the prescribed planting installation seasons. Ed Snodgrass of Emory Knoll Farms was an instrumental consultant to HOK with the plant selection. Brandon Hartz of HOK explained that Ed’s expertise helped in two ways.
First, Ed provided recommendations and insight to the vast plant list from the initial RFP. In doing so, HOK reduced the plant list by 1/3, removing plants that would not thrive on the roof. Secondly, with Ed’s knowledge of nurseries and nurserymen, HOK was able to select plants that could actually be grown and supplied to such an extensive roof. Actually the roof is more “semi-intensive,” but that’s just semantics.
The second challenge was the hot DC summers and ensuring the plants receive sufficient water during their establishment period. Gordon hired an irrigation contractor to install the specified drip irrigation and a comprehensive overhead irrigation system, of their own design. Gordon did not feel that the drip system would be sufficient to protect the plants during the summer heat. The drip system utilizes gray water from a stormwater wet pond, which, according to Brandon Hartz, was primarily intended to provide long-term water for the grasses and shrubs planted in the deeper soils (12”-18”).
Brandon explained further that the overhead sprinkler system is only intended to be used during the plants’ establishment period and will be removed twelve months after substantial completion in order to be in compliance with LEED, since it uses potable water.
Since the building is terraced into the hillside, the site provided unique challenges and appealing solutions. HOK’s landscape design intent was to allow all the offices that look over the DC skyline to enjoy this view unobstructed by distractions such as mechanical equipment and to be able to enjoy the vegetative roof.
Hardy Sedum mats are planted around the perimeter of most of the roofs. The effect of the Sedum mats at the roof perimeter provides a neat and tidy edge to the wilder grasses and shrubs in the mounded areas in the middle. You can start to see this coming together in the photo below:
|Vegetated mats and herbaceous grasses and shrubs.|
To provide an idea of the order of magnitude of the project, the list of plants is as follows: 430,000+ 3" square by 5” deep plugs, 78,000+ square feet of Sedum mats, and 2,000 shrubs in 1 gallon sizes of multiple species.
The long-term maintenance was given considerable thought, as it should be on every VRA. In addition to the very sustainable drip irrigation system utilizing on-site water, HOK worked with Clark to determine which of the roofs would be the least accessible, and thus most difficult to maintain. These roofs were then planted exclusively with pre-grown sedum mats supplied by Sempergreen of Stevensburg, VA, and are pictured here:
|Pre-vegetated Sedum mats over this VRA.|
The United States Coast Guard Headquarters DHS St. Elizabeths Campus project is scheduled to be completed in Q1 of 2013. Once complete, the total VRA area of 400,000 square feet will not only look great, but also retain stormwater that would otherwise combine with waste water that may bypass the Blue Plains Wastewater Treatment Plant, just downstream from the site. In DC, the CSO is breached with any rain event over ¾” and untreated sewage bypasses Blue Plains.
|DHS St. Elizabeths Master Plan.|
Landscape architecture and graphic source: SmithGroup JJR.
In June 2011 it was awarded the James D.P. Farrell Brownfields Project of the Year Award. Additionally, this campus of VRAs will help the project reach a LEED Gold certification status.
|Panoramic view of the DHS St. Elizabeths Campus progress in December, 2011.|
Photo source: Clark Construction
The Coast Guard says its presence and impact is local, regional, national and international and that they are "a unique instrument of maritime safety, security and environmental stewardship.” Greenroofs’ or VRAs’ ecological impact can also be appreciated at multiple levels, and the Coast Guard’s commitment to the environment is clear with the many eco-friendly attributes of their new headquarters complex.
VRAs have become a permanent part of the landscape here and are certainly a growth niche in the industry (pun intended). You can see more on this unique project at: http://www.uscgproject.com/ and click here for the full Sustainability Summary PDF.
|The U.S. Coast Guard HQ at the DHS St. Elizabeths Campus.|
Graphic by Perkins + Will. Source: Clark Construction.
Publisher's Note: See the U.S. Coast Guard HQ at the DHS St. Elizabeths Campus project profile in The Greenroof & Greenwall Projects Database here.
Northeast Regional Building Science Specialist
Todd C. Skopic, CSI, CDT, LEED AP, is the Northeast Regional Building Science Specialist with the Henry Company. Todd has been involved in the design and construction industry for 26 years. Todd has specialized in water, moisture and air intrusion prevention into the building envelope. Additionally, Todd has become an industry expert in vegetative roofing and has personally been involved in the design, specification and installation of many vegetative roofs. Todd has given hundreds of presentations to owners, architects, consulting engineering firms, and general contractors over his career.
Between this project and the City Center project, also in DC, the Henry Company has close to one million square feet of VRAs under construction in the DC market alone.
Contact Todd at: firstname.lastname@example.org and 410.960.3059.
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