Second Skin
The Big Green Screen
Like the Liverpool Department Store’s skin, the new facade of the Edith Green/Wendell Wyatt Federal Building in Portland, Oregon, encases a conventional structure in an embellished exterior. But instead of the solid armor of the Mexican store, the Portland project has a metallic veil. The facade, now almost completely installed, is part of a $133 million renovation, slated for completion in 2014. The overhaul is expected to earn the 18-story, 1976 precast-concrete office tower a LEED Platinum certification and help it comply with current security standards.
The revamp, designed by a pair of Pacific Northwest firms—Portland-based SERA Architects and Bainbridge Island, Washington–based Cutler Anderson Architects—encases the structure in a high-performance double-glazed glass curtain wall that is both energy-efficient and blast-resistant. The scheme also includes a shading screen for the building’s west elevation. By adding the screen, the project team was able to significantly reduce solar gain and maintain occupant comfort with radiant heating and cooling. Without the shading device, the building would have required more cooling capacity and a much less efficient VAV (variable air volume) mechanical system, according to SERA associate principal Lisa Petterson.
The client, the General Services Administration (GSA), rejected an early scheme for a living wall that included climbing vines due to concerns about maintenance and the two-year time frame required for the plants to grow to full shading capacity. However, James Cutler, Cutler Anderson principal, wanted to maintain the screen’s organic look. In collaboration with cladding fabricator Benson Industries, he developed a system of six bowed arrays made up of extruded aluminum reedlike members. The reeds vary in size and are combined in a manner that allows the screens to be fabricated readily but lends them a slightly random quality.
The team relied on BIM (building information modeling) to get all the details worked out quickly. “It was critical to be able to see the design in 3-D and in context with the other conditions,” says SERA’s Gauri Rajbaidya. The modeling software allowed both the architects and the fabricators to articulate the design and refine it swiftly.
The west elevation’s screen responds to the low-angle sun and is devised to shade 50 percent of the glazing at peak solar exposure, according to Petterson. “It needed to be a vertical scenario, but the south and east facades—which are actually oriented southeast and southwest—required a combination of horizontal- and vertical-shading systems.” The result is that each facade is articulated in response to its specific orientation. For the south and east elevations, the reeds were adapted to create vertical finlike screens that bracket either side of horizontal light shelves. The 2-foot-deep light shelves shade the lower portion of the windows and reflect daylight into the building through upper windows.
SERA worked with the University of Oregon’s Energy Studies in Buildings Laboratory to analyze the shading and daylighting system. The architects tested several facade configurations in an artificial sky—a chamber that simulates overcast skies—to assess daylighting levels. The team also placed a partial-facade mock-up on a rotating table called a heliodon, which replicates sun angles at a given time of year. The data allowed the designers to fine-tune the screen and the light shelf systems.
The tubular reeds would have been 280 feet tall if they were continuous. But because aluminum has a relatively high coefficient of thermal expansion (a metric that describes how materials respond to temperature changes), designers needed to develop an assembly that would allow the reeds to expand and contract. They divided the tubes into roughly 30-foot-long sections that span between horizontal supports spaced every two floors or 25 feet. Each reed cantilevers several feet above and below the supports, creating a rhythmic pattern. “We spent so much time on these joints because you see them when you look out the window,” explains Cutler. “They’re right in your face.”
The reeds are trapezoidal in plan, splayed so that the narrower face is on the interior. Besides meeting the shading needs, the splay is meant to reduce the feeling of enclosure. The tubes, which vary in depth from 3 to 5 inches, also have a slightly “pillowed” front face and rounded corners. Sharp corners would have created sharp shadows and emphasized the tubes’ barlike nature, explains Petterson.
As with the Liverpool Department Store, it’s the chorus of thoughtful details that make the facade sing. Both projects illustrate how the technology of modeling programs, BIM, and computer driven fabrication have broadened possibilities for the architect. They also demonstrate the value of collaboration between architects and fabricators in realizing complex design concepts.
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