The Building Team responsible for Des Moines Central Library embraced the notion of designing a simple library in the park. London architect David Chipperfield took that idea and ran with it, designing a modern, monolithic structure wrapped in a shimmering high-tech copper skin that sits in Western Gateway Park, a 13-acre brownfield site that's the centerpiece of the Iowa capital's downtown redevelopment.
At 117,000 sf, the new two-story central library is triple the size of its former home in a 1903 Beaux Arts building. Its new program was equally ambitious in size and scope, thanks to input from library trustees and administrators, the City Council, and the people of Des Moines.
Although the library didn't open until April 2006, the building's 55,000-sf vegetated roof was planted in 2005. The roof's hardy leaf succulents are expected to reduce storm water runoff by as much as 25%. Photo: Farshid Assassi.
The Building Team, which included Chipperfield and local firms HLKB Architecture, KJWW Engineering (MEP engineer), and The Weitz Company (construction manager), was asked to think beyond the traditional library model and create an innovative civic landmark that serves as both a benchmark for the city's future green building efforts and as an integrated community learning and resource center.
The library's triple-pane copper glazing is its most distinctive feature. A 2mm copper screen is laminated between two outer panes, and the 4x14-foot, double-stacked glass panels cover 80% of the library's façade. At times the building appears translucent, while at other times it seems clad in solid metal panels. The building's floor-to-ceiling windows offer dramatic views of the park, giving those inside the building the sense of being outside.
The location of the book stacks toward the center of the building and parallel to the urban grid also preserves views out to the park and allows study and lounge spaces to be organized along the perimeter windows. (Chipperfield himself designed the library's lounge furniture to cut costs. His “Des Moines Suite” includes 120 lounge chairs, foot stools, and side tables; total cost: $72,000.) The generous glazing also helps the library capture the proper amount of natural light for comfortable ambient light levels. The daylighting easily filters into the building's center aisles thanks to a long, thin floor plan.
The translucent façade posed serious concerns with regard to heat gain and glare. KJWW's engineers tracked the sun's angle at specific times of the day throughout the year to determine how best to position the copper screen to reduce UV radiation and interior glare. Final screen positions block 83% of harmful ultraviolet rays. In fact, the screens proved so efficient, they eliminated the need for secondary sunshading and are expected to produce 29% energy savings over similar code-compliant structures, according to an energy-use model conducted in 2002 during the library's planning and engineering phases.
The library's additional high-efficiency features include a 55,000-sf vegetated roof that reduces stormwater runoff by as much as 25%; motion sensors that automate the building's lighting; energy-recovery ventilators with an 80% energy-recovery rating (the ventilators also retain enough moisture to eliminate the need for separate humidifiers), and an underfloor HVAC distribution system. (In the children's area, translucent acrylic floor tiles were installed so that the children could see the ductwork and learn how the system worked.) The local utilities were so impressed with the building's HVAC systems they granted the library $80,000 in rebates.
Since opening in April 2006, library visits are up 218% and materials circulation is up 128%, so the community is clearly embracing its new learning and resource center. Library services include 151 public computer terminals, wireless Internet, a 28-station computer lab, children and teen centers with flat-screen TVs, a community meeting room, a café, and even a drive-through window for material drop off and pick up.
All those services are integrated within a highly flexible floor plan that was specifically engineered for maximum use of interior space. The building's center has 600-mm diameter columns on a 9-mm grid to carry the heavy loads of the book stacks, while the perimeter has 400-mm diameter columns at 6-mm centers. The concrete slab floors are 450 mm thick. Most of the concrete was left exposed to reflect Chipperfield's penchant for minimalism—and it didn't hurt that it helped save on finish materials costs.
In fact, this “simple library in the park” was completed for just $32.3 million—$185/sf, compared to an average $225/sf for new libraries, according to a review of peer institutions conducted by the project's consultants.
“Doing anything monolithic is difficult, and the effectiveness of the restraint shown here is admirable,” said jury member John Durbrow, AIA, professor at the School of Architecture at Illinois Institute of Technology, Chicago.