Handcrafting the Census Bureau's Hardwood Veil
Jim Whitaker will never forget the day he first met Maurice Rhude.
It was early 2004, and Whitaker and his design-build team from Skanska USA Building Inc., Parsippany, N.J., were frantically searching for a wood fabrication facility that could execute an ultra-ambitious exterior design scheme for the planned $331 million U.S. Census Bureau headquarters in Suitland, Md.
The design, dreamed up by architects at Skidmore, Owings & Merrill, called for 16,000 curving wood fins in four custom shapes to be mounted on the precast concrete façade, thus creating a dramatic wood “veil” around the 2.5 million-sf, eight-story structure. The one-of-a-kind treatment would not only serve as a sunshade for the office space, but also help mask the massive concrete structure and create an unusual, daring aesthetic that would tie in with the heavily wooded parkland nearby.
“We were literally combing the planet looking for facilities that could mill vast quantities of lumber and bend it into unique shapes. Fortunately, we stumbled upon Maury,” says Whitaker, a member of the AIA and the Design-Build Institute of America and a VP with Skanska, which teamed with Dallas-based HKS Inc. as the design-builder for the project. “He flew down from his mill in northern Wisconsin and told us all the shipbuilding stories from World War II. He was one of the line laborers, running white oak through saws way back in the 1940s.”
On nothing more than a handshake, Rhude and his team of old-world craftsmen at Sentinel Structures, Peshtigo, Wis., agreed to take on the job. The mill had long ago moved from shipbuilding into the manufacture of glue-laminated timber structures, including bridges and roof members. The scale and complexity of this job would push the mill to the limit. Milling production lines that had been out of commission for decades would have to be fired back up to handle the extra load.
For two years straight, Sentinel's mill operated at full capacity, as Rhude and his team methodically milled, glued, and bent white oak into the prescriptive, undulating forms specified by SOM. The fins, which measure 13 feet tall, 11 inches wide, and 2¼ inches thick, are composed of seven layers of the white oak bonded together using high-performance adhesive and formed into the precise shapes using custom-designed jigs.
Having to deal with the unknowns of this labor-intensive, workshop-like approach for creating the wood veil was a major concern for the design-build team, which was operating under a lump-sump, fixed-price contract with the General Services Administration that also included a set grand opening date. “No sophisticated management tools applied here. Maury just said, 'We'll be done when we get it done,'” says Whitaker. “We were holding our breath half the time while woodwork was going on.”
Meanwhile, architects and engineers at SOM and HKS were busy tackling another major problem: how to mount the individual wood fins to the building's precast concrete façade.
The solution involved commissioning a steel fabricator to build more than 1,300 stainless-steel metal frames, each designed to hold a set of five to six wooden blades. The fins were shipped from Sentinel's mill to the fabricator's workshop, where they were bolted to the frames. The prefabricated panels were then shipped to the site, craned into place, and mounted onto stainless steel anchors that were designed to support the dead loads and wind loads.
SOM devised a predetermined position for each wooden blade on the frames and for each panel on the exterior. The four different fin shapes were rotated front to back and top to bottom to create 30 different panel combinations on the façade. The result is a totally random and somewhat chaotic pattern.
“If you stare at the façade long enough you can start to see the repeats, but you have to really spend time to find them,” says Gary Haney, SOM's partner-in-charge on the project. Haney likens the experience of walking or driving past the building to that of strolling past a picket fence. “The building has an illusionist quality, it opens and closes as you walk by, and at certain angles it looks like a solid piece of bark.”
SOM specified straight blades for the east and west façades to further accentuate the “picket fence” effect. This was especially the case on the east façade, which faces Silver Hill Road, a busy thoroughfare that borders the headquarters. The agency's name is displayed in bold, black letters painted on a series of fins that span across the top two floors on the east exterior, creating a “dynamic 3D wooden billboard,” says Haney.
From ironwood to white oak
SOM originally specified ipe wood for the fins because of its natural resistance to rot, decay, insects, mold, and even fire. Known as “ironwood,” ipe is among the strongest and densest wood species on the planet. However, the size of the project posed a potential supply problem.
“We wanted to carry out SOM's design intent as closely as possible, but by the time we reached the construction documents phase we realized that there just wasn't enough sustainably harvested ipe on the planet to meet out needs,” says Jeff Vandersall, AIA, HKS's project manager. The wood had to be SFI-certified, because GSA is applying for a LEED Silver rating with the U.S. Green Building Council. On top of that, ipe's high-density fiber structure is resistant to lamination, a key requirement for forming the curving, undulating shapes of the fins.
“White oak was the next-best wood that was available in the quantities needed,” says Vandersall. “It's a domestically available wood species that has many of the same characteristics of ipe with respect to strength, aging, rot-resistance, and insect repellant.” The wood was harvested from sustainable sites in Indiana, Missouri, and West Virginia and shipped to Sentinel Structures for milling.
The team used ipe where possible, including for the straight blades on the east and west façades and for traditional wall and roof planking (installed by ISEC Inc., Englewood, Colo.) on several “jewel box” buildings that jut out from the main structure.
Whitaker says applying for a building permit was an “interesting experience” given the vast amount of wood planned for the exterior. “Traditionally, wood does not fit within the model code requirements with respect to commercial office construction, especially on the exterior,” says Whitaker. “As you could imagine, we turned some heads when we showed up for a building permit and explained that we were planning an eight-story office building that will house 6,000 people, and 'Oh, by the way, we're going to hang wood all around the exterior, but there's no need to worry about it.'”
Fire safety was the main concern expressed by city officials and the local fire marshal. GSA commissioned extensive flame-spread and computer modeling tests to prove that the wood exterior would not be a liability.
Because ipe is noncombustible, the ground-level wood-clad jewel boxes were given the OK. However, concerns raised about the performance of the white oak forced the team to start the veil above the first floor, roughly 18 feet from ground level, to avoid having a ground fire spread to the oak fins.
'And then the pigeons came'
Just when the Building Team thought it had all angles covered, Mother Nature stepped in.
“As we began installation of the panels, the pigeons came,” says Whitaker. “It turns out that the half-inch-wide anchor brackets that support the wood veil provided a perfect place for birds to roost.”
Skanska quickly altered the design, adding a bird deterrent system that consists of a small cluster of spikes fastened to each bracket.
U.S. Census Bureau Headquarters Suitland, Md.
Owner: U.S. General Services Administration
Architects: Skidmore, Owings & Merrill (design architect); HKS Inc. (AOR); Metropolitan Architects and Planners (associate)
Design-builder: Skanska USA Building (with HKS)
Structural engineer: Walter P Moore
Mechanical/electrical/plumbing engineer: Southland Industries
Specialty woods: Sentinel Structures
Area: 2.5 million gross sf
Construction cost: $331 million
Construction time: September 2003 to January 2007
Delivery method: Design-build bridging