Texture on glazing
Inside the 353,000-square-foot Minneapolis Central Library, sunlight filtering through screen-printed glass panels creates an ever-changing pattern of shadows. “When you are in the library, there’s a playfulness of having the sunlight come in through the fritted glass,” says Tom Hysell, principal at Architecture Alliance, Minneapolis. “The light and shadows play across the floor and the bookshelves.”
Cesar Pelli of Pelli Clarke Pelli Architects in New Haven, Conn., designed a public space where glazing plays a critical role in creating a warm environment that celebrates the joy patrons find in the printed word.
Pelli’s signature treatment of glass becomes apparent to patrons even before they enter. Each face of the five-story building features fritted walls that honor Minneapolis’s natural surroundings. Thousands of screen-printed glass panels combine to depict prairie grass on the west elevation, thin birch trees on the east and snow-covered tree branches on the south. Flowing water on the north side mimics the Mississippi River the library faces.
The images and treatment of the glass represent one design element that defines the library’s personality. Hysell, the project’s architect of record, suspects that “using the glass as a motif in that way
hasn’t been done to that level or magnitude before.”
Viracon created screen-printed panels based on digitized nature photos selected by Pelli. On previous Viracon projects involving screen-printed applications, just a few screens were required to complete an image; Pelli’s designs for the library required 50. To create multistory-tall images, Viracon workers printed the pictures on more than 4,000 glass panels at its Owatonna, Minn., plant. After the white ceramic-frit paint was applied to the panels, a 1,100-degree Fahrenheit tempering process permanently fused the artwork to glass.
HKL Cladding Systems Inc. of St. Paul, Minn., managed the exterior façade, glass and glazing. “Four elevations and four different Minnesota seasons and scenes are represented,” says Kurt Larson, chief financial officer, about the library’s exterior presentations. “You go to the first floor of the east elevation, it’s the base of a birch tree. By the time you reach the fifth floor it’s the top of the tree. You see the birch tree’s rise to full height over the screen glass.”
In addition to creating an aesthetic appeal, the semi-opaque panels also serve a practical purpose. During the two-year fabrication process, Viracon coated the low-iron glass panels with several layers of an optically thin coating to control heat gain. The opaque snow-pattern treatment on the library’s south side—where the sun’s exposure is most intense —blocks 80 percent of the solar heat gain. On the opposite side of the building, the images of water ripples block only 20 percent of the solar heat gain.
HKL created 1,400 window-wall units that were used to fasten the screened panels to the exterior. The biggest challenge was more administrative than technical, Larson says. “You would have to track those specific units so you could put the right parts in the right place. It was the toughest part. You have a giant jigsaw puzzle.”
The façade includes the glass in an aluminum frame and a Minnesota dolomite limestone base. With the services of the Construction Research Laboratory in Miami, HKL executives coordinated a performance test to make sure the system worked as designed.
Installation of the panels required a project-specific approach. “We hired Amerect, located in Newport, Minn., to install the window-wall system,” Larson says. “Although the windows were designed to be set from the interior of the building, the raised floors required workers to use a custom tower crane to set all the windows from the outside.” The sophisticated equipment allowed the panels to be set by a single man; installation was completed in four months.
While the screen-printed images are clearly defined from a distance, the interpretation of the art changes when visitors stand within arm’s length of the vertical surfaces. “Walking up the images, they are literal, but when you are right next to them, they change,” Hysell says. “The pixilated images remind you of digital information presented as zeroes and ones.”
Pelli also used glass to create dramatic entrances on both sides of the library. Five-story canted curtain walls at the entrances contain low-iron insulating glass panels supported by thin stainless steel frames. The west-side curtain wall under the library’s distinctive winged roof contains a network of hot-water pipes to heat the glass during Minneapolis’ often brutally cold winters.
Although HKL Cladding and Viracon work on projects across the country, the Minneapolis Central Library sits in their backyards. “It was much easier to be involved in the job because you were here every day,” Larson says. “On the other hand, sometimes running projects at home has its drawbacks because you know too much about what’s going on with a day-to-day basis instead of stepping back and managing from a 20,000-foot perspective. It was exciting to work on a high-profile job with one of the world’s renowned architects.”
Kurt Larson, HKL Cladding Systems Inc., 1851 Buerkle Road, St. Paul, Minn. 55110, 651/482-0369