Cesar Pelli has shown an appreciation for light and translucency in many of his building designs, and his recent work on the Minneapolis Central Library—a neo-modern structure made of glass, metal and stone—has proven to be no exception. 

The $138.7 million, 353,050-square-foot library, which opened to the public in May, was designed through a collaboration of the Minneapolis-based Architectural Alliance (the project’s architect of record) and Pelli’s firm, Cesar Pelli and Associates (now Pelli Clarke Pelli), of New Haven, Conn.

“He clearly and brilliantly went over the top with glass on this project,” said Architectural Alliance managing principal Tom Hysell of Pelli’s design.

The library’s exterior includes a custom, pre-glazed, unitized glass wall system along with two individual curtainwall systems. In addition to an abundance of glass walls, railings and stairway risers, the building’s interior also includes a massive channel glass installation. 

The exterior glass wall system has attracted considerable attention for its abundance of custom-designed, silkscreened, ceramic-fritted glass. The system contains approximately 4,600 units of 1-inch, low-iron, insulating glass panels fabricated by Viracon Inc. More than 50 individual silk-screen patterns were applied to the number two surface of many of the units using Viracon’s Viraspan V175 white ceramic frit paint. The fabricator’s Solarscreen high-performance, low-E coating was also applied to the number two surface. 

In the Details
The silk-screened images represent four specific Minnesota nature scenes, one for each side of the building. The frit was applied in 1/8-inch, rectangular pixels based on computer-generated abstractions of nature scenes selected by Pelli.

In addition to their aesthetic appeal, the varying density of the silkscreened patterns and varying degrees of coverage serve to reduce glare and help optimize the building’s energy performance. 

The frit pattern on the building’s east and west elevations offers abstracted depictions of birch trees and prairie grasses and provides 60 percent coverage. The south elevation, which depicts a snow-covered forest, provides 80 percent coverage to reduce solar heat gain in the summer. On the northern elevation where water is depicted, coverage is reduced to 40 percent.
 
An alternating 4- to 6-inch offset in the glass plane provides a sense of texture to the window walls, while a contrasting pair of fritted pinstripes running parallel to each unit’s lower vertical mullion infuses a sense of harmony. 

Support Systems
The library’s two curtainwall systems feature unique structural support mechanisms, the larger of which is hung from the building’s ornamental “wing,” a sculptural rooftop feature that extends across the busy downtown streets on both the library’s eastern main entrance and western back entrance. 

The curtainwalls were made from low-iron, low-E glass manufactured by Saint-Gobain.

A hanging structure composed of steel and stainless steel supports the glass units on the wider east entrance. The support system includes a series of multi-story, steel-frame bridges that not only link the atrium’s northern and southern ends, but also provide lateral support and transfer the gravity load to steel tension rods. Stainless steel columns support the narrower curtainwall that hangs above the library’s west entrance. 

Also unique to the building’s curtainwall systems are stainless steel support tubes that circulate spent warm water, inhibiting frost and condensation during colder months. 

On the Inside
The innovative design continues inside and includes customized metal cladding and ornamental grilles throughout the building, as well as a custom fire-rated window wall system on the ground floor, a custom, sliding panel display system on the second floor, four glass fireplace surrounds, balcony and bridge glass guard railings with stainless steel stanchions and a structural ¾-inch glass guard rail system for the library commons stair. 

Perhaps most remarkable about the project, in terms of interior glass however, is the building’s large, impressive configuration of channel glass in the library’s atrium. It is a vast, open area of balconies and bridges that join the building’s north and south wings. 

“Originally, it was supposed to be a standalone channel glass system that married up to a typical storefront-type system,” said Mark Meyer, project manager for the interior contract glazier Harmon Inc. “But when we talked to Architectural Alliance, we realized they were looking for a more seamless look with a smaller build-up of metal mass. So we designed mullions that could carry either ¼-inch glass or channel glass. 

“We used the same mullions, the same gaskets and everything and designed a system that could handle all of the existing doorways, hardware requirements and wiring routes,” he explained. 

With more than 3,000 lites measuring more than 32,000 square feet, it’s the largest installation of channel glass in the United States. The Linit brand channel glass units were manufactured by Lamberts Glasfabrik in Wunseidel, Germany and distributed in North America by Bendheim of Passaic, N.J. 

With a thickness of 6 mm (about ¼ inch), each roughcast unit measures 33 mm wide (about 13 inches) and has a 41-mm (about 1 ½ -inch) flange. The bulk of the units are tempered glass certified by the Safety Glazing Certification Council (SGCC), with floor-to-ceiling heights reaching 19 feet. 

During the project’s initial planning meetings, when Pelli and his design team met with library patrons to discuss their needs and desires for a new central library, the team fielded repeated requests for a landmark building that was not only architecturally significant, but also friendly, warm and inviting. The design team answered by creating a glistening edifice that is flooded with pure, natural light by day and sparkles like a gem against the cityscape at night.

USG
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