The Des Moines Art Center, designed in 1948 by Eliel Saarinen, consisted of a U-shaped single-story gallery plus a double-height gallery to the west terminated by a two-story annex. In 1965 I.M. Pei added a block to the south facing a public park, thereby closing the original U-plan to create an internal sculpture court. The site for this present addition is primarily to the north of this two-stage complex. Because the Saarinen building is visible from the downtown approach, the challenge was to design an addition that would respect the generally horizontal profile of the center.

The addition was designed as a series of separate volumes to accommodate the required expansion without producing a large mass. Thus three new additions were located around the existing complex in such a way as to reinforce the formal order of the Saarinen scheme. A new courtyard pavilion strengthens the east-west entry axis of the existing museum. The pavilion accommodates the restaurant and meeting room and activates the previously underused court by opening it to the patio in warm weather.

A glass-enclosed link running along the north-south axis connects to the new northern addition, which houses most of the additional gallery space. Volumetrically separate from the Saarinen building, this larger increment is vertically condensed and leaves the preferred view of the existing museum unobstructed. The largest of its three levels is located entirely below grade with slots admitting natural light into the temporary exhibition gallery.

The overall plan in this addition derives from a nine-square grid, in which the central square provides a four-column internal atrium lit by clerestory windows and perimeter skylights. This cubic volume is sheathed in granite and covered by a flattened pyramid that serves as a foil to the butterfly-section roof employed by Pei. A third smaller addition accommodating services and additional gallery space above is attached to the west wing of the Saarinen building. In this way the components of the complex designed by Saarinen and Pei were amplified by three discrete additions of different sizes.