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green@work : Magazine : Back Issues : Mar/Apr 2007 : Case Study

Case Study: Joining Together for Gold
It took hundreds of professionals and a lot of teamwork, but the mixed-use One and Two Potomac Yard in Washington, D.C., has achieved the USGBC's LEED Gold certification.

by Douglas Carter, AIA


 

Bold is not an element, but a compound, when it comes to sustainable design. A LEED Gold-level certified building is designed and constructed from literally hundreds of integral components. Moreover, turning bricks and mortar into Gold requires the combined work of a large team of specialized professionals working together from the conceptual stage of a project through its completion.

One and Two Potomac Yard in Washington, D.C., is a case in point. Opened in May 2006, the project earned the Leadership in Energy and Environmental Design (LEED) Gold level of certification for new construction or major renovation by the U.S. Green Building Council (USGBC). The project is one of the largest LEED Gold-certified office buildings on the east coast.

The Energy Star-rated building is designed to use 20 percent less energy and 40 percent less water than comparable new buildings. Buildings are oriented to take maximum advantage of the sun and expansive views of the Washington, D.C., area. Thermopane-glazed floor-to-ceiling windows combined with an open-plan interior admits abundant natural light and affords a direct line of sight to the exterior for 97 percent of all the spaces in the buildings. Sustainable mechanical and electrical systems, regional and recycled materials, and “eco-friendly commuting” amenities—including parking for 100 bicycles, adjacency to mass transit and 30 electric-vehicle charging stations—are integral components of the project. In fact, attention to the environment made One and Two Potomac Yard a natural fit for the Environmental Protection Agency (EPA), which leases 405,000 square feet of office space in the two buildings. Altogether, One and Two Potomac Yard provides 654,000 square feet of office space.

Situated next to Reagan National Airport and the Virginia Railway, the project is made up of two adjacent 12-story buildings with sweeping views of the airport, the Potomac River and the U.S. Capitol. The two buildings are connected via a green-roofed pedestrian walkway and provide six levels of parking, with three below grade. Amenities include ground-floor retail space and a fitness center for the exclusive use of tenants. The buildings are mirrored in design, projecting a strong and dignified appearance that is both professional yet welcoming.

A Sustainable Site
Attaining any one of the five LEED certifications requires excellence in six categories: Sustainable Sites, Water Efficiency, Energy and Atmosphere, Materials and Resources, Indoor Environmental Quality, and Innovation and Design Process.

Ideally, the project begins with a sustainable site. In this case, the developer, Arlington, Va.-based Crescent Resources, LLC, acquired the old Richmond, Fredericksburg and Potomac Railroad yard, which had been declared a Brownfields Redevelopment site due to years of hazardous contamination from the railway. Following several years of extensive environmental remediation, construction began on One and Two Potomac Yard. Originally designed as conventional office buildings, the developer made the commitment to redesign and build an environmentally sustainable building. Crescent promotes strong environmental guidelines for all of its projects.

One and Two Potomac Yard is also designed to meet the emerging needs of transit-oriented development in this area. The development is near a Washington Metro station, and a new bus stop was developed for this project. Additionally, a new rapid transit bus line is planned.

Architectural firm Davis, Carter, Scott’s knowledge of LEED design and practices was integral in making the conversion from a conventional building to a certified one. As architect of record, Davis Carter Scott worked closely with the design architect, Pickard Chilton Architects, Inc. of New Haven, Conn., as well as Crescent Resources to ensure the project would meet LEED and Arlington County requirements. Like many municipalities, Arlington County is committed to sustainability and offers incentives to achieve it. In Arlington, a design that is capable of achieving a LEED Silver certification may be granted a 0.25-increase in density. Indeed, if a project is subject to design approval, the county requires that the project be LEED-certifiable at a minimum. In this case, when the General Services Administration (GSA) indicated interest in leasing space for the EPA, Crescent Resources made the commitment to attaining Silver certification. When the EPA committed to becoming a tenant, in turn, the developer committed to attaining Gold.

Up-front involvement by all these stakeholders allowed the project team to balance the needs of the tenant, owner and county. This is an example of the need for early participation and communication to bring such a project to fruition.

Daylight, Views and Energy Efficiency
To achieve optimum daylight and views, it is important to orient the building effectively. At Potomac Yard, Center Park runs north to south in the midst of all of the buildings, so all buildings can afford views over the broad expanse of the Potomac River, over Center Park, or over a wide stretch of the Route One corridor.

Then the design focus shifts to bringing daylight into the building. There are a couple of strategies normally used on the exterior of the building, including light shelves, which is a well-accepted technique that bounces light into the building. However, use of light shelves tends to require greater ceiling heights, and this project was subject to strict height limitations. Moreover, Arlington County’s design guidelines encourage punched windows rather than a ribbon-window approach. The solution: floor-to-ceiling windows in combination with an open-plan interior, which admits abundant natural light and affords a direct line of sight to the exterior for virtually all of the spaces in the two buildings.

Maximizing penetration of daylight also allowed the use of light fixtures with daylight sensors, which reduce wattage when natural light levels permit. In turn, this reduced the amount of energy required to cool the building year-round. Moreover, precise load calculations of lighting and office devices were crucial to optimizing the design of the HVAC system. As a result, in this project the design team was able to reduce energy use 20 percent compared with the accepted performance criterion of ASHRAE 90.1 for comparable new buildings. Designed with energy-efficient mechanical system components, the system comprises a central chilled-water cooling system, carbon dioxide monitoring system—contributing to good indoor air quality (IAQ) by optimizing ventilation—and thermal comfort system with additional humidity control. Moreover, the mechanical systems contain no chlorofluorocarbons (CFCs).

In addition to the carbon dioxide monitoring system, use of materials low in volatile organic compounds (VOCs) is another integral component to IAQ. In this project, all paints, adhesives, sealants, floor coverings and composite wood products are composed of low or no VOC-emitting materials.

From Design through Construction

The use of sustainable new and recycled materials creates a more sustainable and efficient building, but can be challenging to implement. The general contractor must be both responsive and responsible in order for the project team to maximize points in this LEED category. The general contractor is responsible for a lot of the documentation that is submitted to the USGBC, and as he procures the materials, he needs to be sure that what is delivered meets the project team’s specifications, and then document this in detail. It takes a very diligent contractor to accomplish this. In this case, the transition from design to construction was made seamless by the early involvement of the general contractor, James G. Davis Construction of Rockville, Md., in the design of the building, which enabled the general contractor’s team to fully comprehend all of the LEED design issues. The general contractor’s implementation of an IAQ construction-management plan also contributed to achievement of points in that category. Overall, the general contractor was able to fully deliver a high-performance building without project schedule delay, while minimizing the cost of sustainable measures for the client.

Sustainable Materials
Use of sustainable materials in the structure, finishes and furnishings is another key LEED engineering and design strategy, and the building structure itself can make a significant contribution. In this project, the post-tensioned concrete structure contains as much fly-ash (a byproduct of coal combustion at power plants) as possible within the constraints imposed by air temperature during construction, and the reinforcement bars contain recycled steel.

With economy and construction efficiency in mind, the architects designed an exterior finish composed of precast concrete panels with a cast-in brick exterior. The bases of the buildings are also composed of a precast base with a granite finish material. Another benefit of precast concrete is its regional availability; in this case, the precast plant is located in Virginia. Interior finishes and furnishings were also specified for sustainability—right down to the workstations, which feature approximately 40 percent recycled materials and corn-based fabrics.

Finally, employing LEED-accredited professionals with knowledge of environmentally sustainable design, materials and construction methods facilitates certification and earns credit under the Innovation and Design process category. Crescent Resources; Davis, Carter, Scott; and Davis Construction employed LEED-accredited professionals on this project.

Literally hundreds of individual components and the work of a team of knowledgeable professionals are required to make LEED Gold. One and Two Potomac Yard is an example for future development, addressing the issues of growing traffic congestion and pollution in the Washington, D.C. region. It is also an example of the significant strides that can be made toward preserving the Earth’s finite resources when a team with a single-minded commitment to sustainable design and construction comes together at the early stage of a project.

Douglas Carter, AIA, is a founding principal of Davis, Carter, Scott Ltd., one of the largest locally owned architectural and interior architectural firms in the D.C. metropolitan area. He can be reached at (703) 556-9275.


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