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Photo © Benjamin Benschneider Photography
The atrium features a reclaimed wood-clad "treehouse," skylights, and a rock garden.


Esprit de Corps

ZGF Architects
Seattle, Washington

Esprit de Corps: Clad in reclaimed wood, a "treehouse" anchors a daylight-filled atrium at the heart of ZGF's gleaming U.S. Army Corps of Engineers Seattle headquarters.

BY James S. Russell
June 2014
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The Duwamish River flows next to the Seattle headquarters of the U.S. Army Corps of Engineers, in an industrial area south of downtown. Although the Corps is responsible for maintaining the nation's navigable waters, the river was essentially invisible to them since they shared a windowless warren of offices with other federal agencies in a former Ford Motor plant.

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All that changed about a year and a half ago when the Corps moved next door to a new 209,000-square-foot building with the ungainly official name of Federal Center South Building 1202. Designed by the Seattle office of ZGF Architects, it opens to generous views of the river and takes natural waterways as a theme. Visitors quickly become aware of the building's proximity to the Duwamish, since the entry lobby leads to a wide hallway culminating in the river view.

The General Services Administration (GSA) was able to proceed with the $74 million project quickly in 2010 thanks to American Recovery and Reinvestment Act funds and a design-build arrangement with Sellen Construction. As part of its Design Excellence program, the GSA set an energy-use intensity (EUI) goal of 27.6 Kbtu/sf per year compared to a regional average of 106. The agency made this ambitious target part of the design-build contract, requiring that the building achieve this EUI in the first year of operation.

After winning a competition for the project in early 2010, a brief 18-week design process by ZGF refined key elements of the LEED Platinum-aspiring project. Clad in stainless-steel shingles that were custom developed to install smoothly along the sinuous facade, the three-story office building curves in an oxbow around a central, wood-clad "treehouse," wrapped by a skylighted atrium. The treehouse is used for meetings and informal gatherings and includes a library presided over by a stuffed moose's head. Stairs and bridges that cross the atrium orchestrate movement and light and shadow.

The removal of a 1,000-foot-long warehouse on the property and remediation of localized areas within its footprint made room for the installation of lawns, meadows, rain gardens, and bio-retention ponds that filter and absorb all of the 4.6-acre site's runoff. "Essentially, everything had been paved," says Rick Thomas, GSA's project manager. A sunken bio-retention pond at the entrance does double duty as a security measure, with the ability to foil the approach of a bomb-carrying vehicle. Unfortunately, the security regime includes a chain-link fence along the water side of the building, preventing river access as well as impeding the construction of a riverside wetland, just the kind of green infrastructure tactic that is entering the Corps' flood-control arsenal.

Massive timbers salvaged from the warehouse support the treehouse, which is clad in reclaimed-wood sheathing. Paint was stripped from 300,000 square feet of timber, which was then further prepared for reuse. Steel plates incised into the hefty structural wood columns bolt into steel beams to form an earthquake-resistant composite structure.

The alluring atrium—with a rock garden that evokes the natural stream environments that the Army Corps increasingly restores to maintain the nation's navigable waters—enables serendipitous encounters. This common space also encourages people to use the open stairs, which advances fitness goals and reduces the need for elevators. (The building only has two elevators, and those are used less than expected.)

The skylights over the treehouse drench the atrium in natural light and help illuminate adjacent office areas. That daylight augments sunlight pouring into the offices from large exterior windows. Even in gray Seattle, solar protection increases efficiency, and tactics include exterior vertical and horizontal fins, tinted glazing, and internal roller blinds. The number of horizontal fins used depends on orientation, and some atrium-facing offices were retrofitted with manual roller blinds to remedy glare and hot spots. Automatically dimming fluorescent fixtures enhance the daylighting scheme.

Finned radiant panels deliver cooling to the mostly open-plan offices using water chilled primarily by geothermal loops integrated in the foundation's piles. The office spaces also depend on heat-recovery for tempering ventilation air, which is supplied at low velocity through floor vents. A thermal storage system using a phase-change material balances heating and cooling loads when needed. In addition to ensuring occupants' thermal comfort, these strategies helped the project team keep the exposed steel-deck ceilings free of ductwork, lending the office spaces an open and airy feel. The treehouse uses independent variable air volume (VAV) air-handling, a system that is more responsive to the varied loads of meeting rooms.

Although the several modes of heating and cooling "were hard to get to talk to each other," according to Thomas, the building, completed in 2012, is performing better than modeled, at an EUI of 25.7. Hitting that number meant getting users on board to reduce plug loads, including discouraging the use of personal coffee makers, microwaves, and portable heaters.

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