Seattle Central Library

New Structure Joins Others Featuring Glass Curtainwall

By Sheila Bacon

The new Seattle Central Library is clad entirely in glass, resulting in a building that not only reflects the architects' unique vision, but also one that is highly energy efficient as well. Photo by Sheila Bacon

Whether it's for form or function, glass curtainwall systems are gaining in popularity throughout Seattle. While Marion Oliver McCaw Hall's clear glass serpentine-shaped wall is eye candy at the renovated opera hall's main entrance, the new Seattle City Hall's glazing system acts as a heat regulation system; warming the building in the winter and cooling it in the summer.

The new Seattle Central Library features the city's latest offering of curtainwall artistry, combining beauty with functionality. The 412,000-sq.-ft. structure is clad entirely in glass, resulting in a building that not only reflects the architects' unique vision, but also one that is highly energy efficient as well.

To understand the idea behind the all-encompassing glass curtainwall, one must first understand the designers' plan for the structure itself. Far from a traditional office building, this 11-story structure is broken into five distinct "platforms" offset from each other and resembling a stack of books. While each platform offers a different service (one is a "mixing area" featuring an auditorium and gathering space, while another houses administrative offices), the all-encompassing glass attempts to visually pull the entire building together.

"The grid was conceived of as a net cast over these offset platforms," said Sam Miller, project manager for Seattle's LMN Architects. Because the glass is essentially clear, those both inside and outside the building can still see the building's separate elements.

The glass- which sits atop a diamond grid structural system and features a static metal mesh in between two panels that acts as a mini sun louver - wasn't always destined to be so transparent. In an attempt to cut costs, the library board at one point decided to implement a tinted glass instead that would essentially act as a pair of sunglasses to shade the building. As the design evolved, however, it was realized that to provide the amount of shading necessary, the tinting would have to be fairly dark, thus negating the architects' vision of having the inside of the building visible from the street. The board decided to splurge on the original metal mesh system.

The metal mesh performs an interesting role; cut in a way that both lets light in and shades it, depending on the angle of the sun. Think of the louvers as vertical blinds on a window. When the blinds are open, people looking out the window barely see the louvers. From a different angle, however, such as that of the sun, the blinds serve to block light. The metal mesh system works similarly at the library. Views into and out of the building are relatively unobstructed, while the sun shining down from above is reflected away from the building.

The louvers' reflective properties help cool the building extremely efficiently, and is one aspect of many that is putting the structure on track to meet the U.S. Green Building Council's LEED (Leadership in Energy and Environmental Design) Silver certification. The design exceeds the city's energy code by 10 percent, and LEED's baseline standard by 40 percent. Buildings striving to meet LEED standards are assigned points for meeting certain "green" guidelines set forth by the council, which will assign the building a rating once completed.

Keeping it Upright

Bounded by Spring and Madison to the north and south, and Fourth and Fifth to the west and east, the $165 million (cost includes the $10 million temporary central library in the Washington State Trade and Convention Center complex) library encompasses a full downtown city block. It replaces the former library, which stood in the exact spot until it was demolished in August, 2001, to make way for the new structure. Construction started in the spring of 2002.

The uniquely shaped structure required a unique method of structural support. While most traditional towers employ a proportioned column grid, this structure uses asymmetrical placement of perimeter and interior trusses, in places cantilevering out to bear on opposing sloped steel box columns. The concrete core and the concrete foundation walls (below 5th avenue) on three sides act to tame the twist that the off-set platforms naturally impose, while the exterior diamond grid system behind the glass "net" serves as the building's seismic support system.

Many of the sloped columns remain visible throughout the building, providing an interesting visual. Jay Taylor, project manager for Seattle engineering firm Magnusson Klemencic Associates, likens the support system to a table top with four legs. If all four legs lean in one direction, the table falls over. If the legs lean in opposing directions, however, the table still remains upright.

The building's design came to the engineers (Magnusson Klemencic and Arup, of London and Los Angeles) as a series of "boxes" pierced by escalators and draped with the diamond grid "tension net". To structurally support that plan, the engineering firms knew additional beams and columns were needed. Instead of imposing a regular column grid upon the structure, engineers started with OMA's bare bones idea and added as few elements as possible to achieve the design. The architects were very open about the engineers' suggestions for the placement of columns, beams and trusses, and the entire design and building team worked closely together to tweak the angle or placement of the support elements so they wouldn't violate the architecture.

"It was fairly liberating as an engineer," Taylor said. "There was never a case of (the architects) saying 'absolutely not' (to our ideas)."

All Aboard

The library is being built using the General Contractor/Construction Manager (GC/CM) method. Hoffman Construction of Washington (Seattle) has been on board from the beginning, something the firm feels is necessary given the unique architecture and the challenges involved in making sure the library is built as is was designed to be.

"The challenge is to produce the architecture envisioned by the architect," said Doug Winn, project executive for Hoffman. "Our job is to let that expression happen."

Winn learned some lessons building unique structures as a member of the Hoffman Construction team that built Seattle's Experience Music Project - the "swoopy" music museum for Paul Allen - back in 1999. In fact, the leaders of the EMP team - Winn, Bob Vincent, Dale Stenning and Mike Martinez - have reunited for the library job. Building a structure with architectural aspects that stray from your typical tower or office building takes a great deal of construction know-how and communication between designers, contractors and subs. Technology comes into play when figuring out angles of columns and the cost of materials, but "it's really a people thing," said Winn. "It's what's between the ears that counts."

Winn credits much of his team's success to a highly capable group of subs and what he calls the "MACC (Maximum Allowable Construction Cost) Tracker," a system of spreadsheets that carefully track the progress of construction and send out red flags when costs exceed what's expected. But moreover, open communication and frequent meetings to talk things through have proven to be the most important.

"I'm a firm believe that numbers and schedules need to hit human brains," Winn said. "This system scratches where people are itching."

Library leaders are excited about the project, and think the future users of the library will be as well.

"I think the public will be really excited once they are able to get inside," said Andra Addision, library spokesperson. "On every floor, there's a connection to the city, with incredible views of surrounding buildings, the mountains and the water. I say it's like Safeco Field - there's not a bad seat in the house!"

Substantial completion of construction is expected in Spring, 2004, with final completion to follow a couple months later.

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