NWF Headquarters

Site Description

Site

Prior to the outset of design, NWF staff from several departments formed a site inventory team to prepare an inventory of the natural features and wildlife on the wooded site and adjacent land.

During design, the design team kept in regular contact with the site inventory team. As the site design progressed and plant selections were made, the design team could draw on the results of the site survey to select supplementary plantings that already exist on the site and those that would be complementary. As work progressed on the "backyard habitats," the team knew what wildlife was already resident on-site and so could design to accommodate it.

Site Design

The site inventory had determined that much of the site vegetation was low quality because of the dominance of invasive exotic plants (e.g., wisteria); however, the northeastern corner contained a flourishing ecosystem with mature high-value vegetation that will be preserved to the greatest extent possible. A half-acre (0.2 ha) tree-save area in the property's northeast corner will prevent at least 30 mature trees—over 30-in. (760 mm) caliper—and associated understory vegetation from being removed.

The team carefully located the building to create the best orientation for daylighting and energy conservation while also fitting with the natural topography and preserving the most valuable trees. The building steps with the steeply sloping terrain, nestling into the topography to minimize the need for excavation and fill.

Parking Reduction

The market standard for parking calls for at least four spaces per 1,000 gross square feet (GSF) (90 m) of a building. After confirming that a future owner could add parking to meet that requirement, NWF opted to develop only 2.6 parking spaces per 1,000 GSF (90 m), the minimum required by the county. The reduction in parking greatly reduces the impervious surface area and protects open space.

Bioretention

Stormwater runoff can pose water quality problems from the release of excess nutrients and sediment from landscaped areas, as well as hydrocarbons from roadways and parking areas. County regulations require that new development include measures to retain stormwater on-site and to improve water quality before it is released. Typical dry ponds often do not integrate well with natural environments because of steep grading necessary to fit them into the site and because plantings are not allowed in the embankment areas, which are actually designed to prevent infiltration. The bioretention area at NWF reduces the need for a larger stormwater retention area, or dry pond.

NWF chose to develop a natural stormwater management system that improves water quality, increases groundwater recharge, and nourishes adjacent Colvin Run, part of the Chesapeake Bay watershed. The natural system provides a diverse environment rich with habitat for wildlife.

Native trees, shrubs, and groundcovers that can handle the ebb and flow of water were used in combinations found naturally in the region, to create a living water filtration system. The low areas will be augmented with seasonal color such as yellow flag iris (Iris versicolor), spicebush (Lindera benzoin), river birch (Betula nigra), and button bush (Cephalanthus occidentalis). To address concerns about employee safety and visibility, taller shrubs will be concentrated at the bottom of the swales.

The parking areas will be lined with curbs with V-shaped cutouts, allowing runoff from the parking lot to flow into two large medians that have been designed as bioretention areas. Runoff from the building roof surfaces will be piped into the bioretention areas. Contaminants suspended in the runoff will be filtered naturally as the water percolates through the soil. In contrast to sand and gravel filtration systems, these living systems will not need periodic replacement.

A dry pond at the low end of the site is designed to control water quantities that exceed what the bioretention areas can manage; water will be retained in the pond and released slowly into a nearby stream. Water flows in the bioretention areas that cannot infiltrate fast enough will flow through underground pipes to the dry pond at the site's lower end. The dry pond will fluctuate with the seasons, retaining as much as 6 feet (2 m) of water during rainy periods and remaining dry at other times.

Backyard Habitats

Well known for its Backyard Wildlife Habitat program, NWF viewed this headquarters project as an excellent opportunity to showcase habitat demonstration areas. The team developed the site to accommodate a diverse range of meadow, woodland, and aquatic wildlife habitats. NWF's objective is for the entire site, even the building's patios and parking lots, to serve as demonstration wildlife habitats.

Landscape architects paid special attention to providing shelter, food, and water for wildlife in each habitat area. The landscape design includes fruit-bearing plants for food, and logs and brush piles for shelter, while the ponds provide water.

The dry pond area and open space in front of the building create meadow habitats, and the park edge on the site's north side is a forest habitat. An aquatic wildlife habitat is located at the building entry; visitors entering the building cross over this habitat on a bridge for a close look. The bioretention area is a habitat that will change over time through natural succession. It started as a meadow and, as the plantings mature, will develop into a forest habitat.

A variety of deciduous native vines that are popular with wildlife, such as Virginia creeper (Parthenocissus quinquefolia), Dutchman's pipe (Aristolochia macrophylla), and trumpet vine (Campsis radicans), climb the trellis structure, providing shade in the spring, summer, and fall. The trellis also promotes NWF's Backyard Wildlife Habitat program by providing a "vertical habitat."

Low-Maintenance Landscaping

The landscaping minimizes the need for irrigation by including only native species and emphasizing those that originally existed on the site. The only water used for irrigation is a drip irrigation system for the vines on the trellis.

The team selected grasses and ground covers that are about 24 in. high (600 mm) and will be mowed only twice per year. Because of safety concerns, an option has been developed that provides a limited mowing zone along walkways and parking lots.

Water

Water-conserving plumbing fixtures are used throughout. Lavatories use aerators and water-metering faucets, while water closets use manually operated flush valves.

Rainwater collected on rooftops and condensate from cooling are routed through the roof drains to the bioretention areas in the parking lots, thereby reducing the quantity of water requiring treatment.

• Lot size: 7 acres
• Previously undeveloped land

Green Strategies

• Development Impacts
  • Limit parking area
• Landscape Plantings
  • Landscape with indigenous vegetation
  • Landscape with plants that provide wildlife forage or habitat
• Managing Stormwater
  • Disconnect roof leaders and storm drains from conventional infrastructure
• Construction Impacts
  • Establish long-term relationship with responsible excavation and sitework contractor
• Siting Analysis
  • Hire a landscape architect to help with siting of buildings and infrastructure
  • Create a map of vegetation on site, including notation of significant specimens
  • Create a wildlife/habitat survey, including links to offsite habitat corridors
• Site Planning
  • Protect and celebrate a site’s uniqueness
  • Site buildings so as to help occupants celebrate the natural beauty

previous topic: Land Use

next topic: Energy

Our thanks to the ENERGY STAR program of the U.S. Environmental Protection Agency, and to the U.S. Department of Energy, and to BuildingGreen, Inc. for hosting the submission and judging forms.

For more information about the AIA/COTE Top Ten Green Projects, contact AIA/COTE. For help on how to use this Web site, contact .