Green Roofs - Living Architecture Monitor - Winter 2009 - (Page 16) PROJECT he National Wildlife Federation® is a conservation organization founded in 1936, during U.S. President Franklin D. Roosevelt’s administration with a mission to inspire Americans to protect wildlife for their children’s future. When the NWF made the decision in the late 1990s to move the organization’s headquarters to a more affordable location in Fairfax, Virginia and into a more compact, environmentally friendly building, every effort was made to minimize the impact on local wildlife and wildlife habitat at the new site. A seven-acre site was chosen in a business park, with the thought the site was destined to be developed anyway. The site was in close proximity to a bus stop and a bicycle trail used by commuters. Most important, the site backed onto a 130-acre conservation area within a 475-acre county park. The architectural team of HOK (Hellmuth, Obata & Kassabaum) designed a building whose long elevations face north and south, to allow for maximum passive solar lighting and heating. The southern, entry-way elevation has large windows and a green wall trellis. The northern elevation has windows that are nearly floor to ceiling in height, affording excellent wildlife viewing in the woodlands behind the building. The shorter east and west elevations are T Initially, the two bioretention ponds were nearly level with the parking area, and they did not drain properly. A deeper trench was then dug, with pillars of sand in the center of each bioretention area. The bottom of each area is now approximately five feet below the parking area and each bioretention pond can hold as much water as a standard 25-meter swimming pool. Waterloving native trees, shrubs and herbaceous plants such as River Birch (Betula nigra) , Spicebush (Lindera benzoin) and Buttonbush (Cephalanthus occidentalis) were placed at the bottom of and on the slopes of the bioretention areas and they offer food, cover and places to raise young to native insects, birds and mammals. Oils and other contaminants from the parking lot and the roof flow into the ponds and percolate through the soil in the bioretention areas, and therefore do not enter local streams. However, county regulations state that the bioretention area may have to be excavated and replaced every 10 years in order to dispose of the contaminants that have accumulated in the soil. As mentioned,every effort was made to preserve,restore or enhance the wildlife habitat value of the site.Meadow areas surrounding the building were created by removing the invasive plants that were present and then sowing the GENERAL BUILDING Architect: HOK Project Consultants: William McDonough & Partners General Contractor: James G. Davis Construction Built: 2000 Occupied: Feb. 2001 Size: 95,000-square-feet GREEN WALL Manufacturer: Greenscreen® Size: Main trellis is 192' long & 38' tall; secondary trellis on balconies of the east end of the building is 12' wide & 38' tall Structural support system: Custom steel structural frame with 147 greenscreen® panels (various sizes), #5132 clips, u.h.m.w. plastic spacers Cost: usd $42,500 opaque. Although much of the property was initially covered with invasive plants, the northeast corner contained many mature trees of over 30 inches in diameter. Placement of the building allowed for the preservation of threequarters-of-an-acre of this mature forest area. In order to minimize impervious surfaces, nwf decided to develop only 2.6 parking spaces per 1,000 gross square feet the minimum allowed by Fairfax County in the year 2000. Typically, a large stormwater retention pond (dry pond) is built to catch the runoff from the parking areas. nwf was reluctant to pursue this course because these ponds have steep sides and provide poor habitat for wildlife. Instead, two bioretention ponds were placed in between the parking areas. This allowed for a much smaller dry pond to be built. Vshaped cut-outs from the parking spaces allow storm water to flow into the ponds. In addition, stormwater runoff from the building’s roof surfaces is piped into the larger of the two ponds. Overflow from the larger pond is piped into the smaller pond. During heavy storms, overflow from the smaller pond is piped into the small dry pond, which has retained as much as six feet of water, but is usually dry. 16 LIVING ARCHITECTURE MONITOR WINTER area with a native plant seed mix.Native herbaceous plants that offer nectar,seeds, foliage,or fruits used by native wildlife were chosen.The area is mowed only twice a year,thus lowering maintenance costs and the emission of greenhouse gases. A multi-level, recirculating-water wildlife pond was created at the entry way, and entrance into the building is achieved by crossing a bridge over the pond. Raccoon footprints of Ranger Rick®, nwf’s famous children’s magazine character, lead across the bridge and into the building. Nesting waterfowl, songbirds, turtles, frogs, snakes and toads have all made their homes in or near the pond. There have been some problems with algal blooms, but it is hoped that the pond will find its own natural balance as aquatic plants start shading the lower pond and decrease the sunlight available to the algae. Perhaps the most innovative habitat-related design of the building is the green wall trellis placed six feet in front of the southern elevation. Seven different species of native, deciduous vines were planted at the base of the trellis. Trumpet honeysuckle (Lonicera sempervirens) was chosen because it is a nectar source for hummingbirds and butterflies. It is also a food plant for the caterpillar stage of the Spring Azure butterfly and the Snowberry Clearwing Moth.
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