This story originally appeared in the June 2009 issue of Azure magazine, and is published at the permission of the magazine. Photos by Gayle Babcock, Architectural Imageworks, LLC.

By any standard, it's a bold project. But for designers to take such risks in the American heartland is particularly unexpected. At the St. Louis offices of Cannon Design, you find yourself in a soaring, 14-meter-high gallery enclosing two tiers of white bands that swoops dramatically around a bend overhead. A third band forms the reception desk on the ground floor.

Cannon Design, an international architecture firm specializing in health care and science centers, has offices throughout the United States and Canada. The St. Louis site constitutes an adaptive reuse of a 1920s coal-fired power station located downtown. Known as the Power House, it's a Cardinals pitcher’s throw from Eero Saarinen's iconic Gateway Arch.

It's also the brainchild of David Polzin, an architect with Cannon Design for more than 10 years. "We needed to expand," he explains. "And we wanted to be closer to street level, to be a part of the community. No one knew we were here."

Polzin is seated opposite one of the spectacular triple-height window apertures that define the original façade. "We're pretty pleased with the result," he says. "But when we first came in here, back in 2007, it was a mess."

The Power House provided coal-fired steam heat to downtown St. Louis. Decommissioned in 1980, the building was known locally as the "weed tree house," in reference to a tree growing out of the roof. Envisioning a space-age office in such a structure took considerable imagination. Cannon Design's principal Tom Bergmann also knew that Missouri offered generous tax credits for the adaptive reuse of historic and brownfield sites. With those credits, the firm could potentially lop an estimated 45 cents off every dollar it spent.

Challenge number one was to design a space that would meet Cannon Design’s desire for a new way of working: one that was intuitive, flexible, and open. Polzin's final design floated two separate floor plates above the ground floor inside the tall volume, thereby creating two extra floors and plenty of collaborative meeting space and workspaces for approximately 120 employees.

In addition, it needed to accommodate an elevator shaft, as well as kitchenettes on each floor, and two staircases located against the back wall in the northwest and southwest corners. And all of it had to be achieved within the historical building envelope. "It was like designing a ship in a bottle," says Polzin.

Within that original framework, a model shop and materials library plus a boardroom are carved out of the basement. On the roof, an oblong structure originally used to store coal conveyor equipment now houses another boardroom and staff lunchroom.

The final design retained the original steel structure: a set of eight columns and trusswork. A new steel system supports the second and third floors, which cantilever out into the ground-floor gallery. These are faced in drywall and painted white. Polzin jokes that the prominent one over the receptionist's desk is his take on the prow of the Titanic. (He acknowledges Alvaro Siza and the UN headquarters in New York as influences.)

They needed to solve a second challenge in remediating the site, removing piles of toxic pigeon droppings and the lead paint covering the load-bearing steel trusswork. "And we found contaminants in the soil near one of the foundations," Bermann says. He and Polzin and their team worked on the project for almost a year; by September 2008, the firm had moved in.

Polzin casts his eye over the hive of office space from a second-floor vantage point. For such an open concept, it's surprisingly quiet – yet there’s plenty of activity.

"Originally, people could look inside this building and see the inner workings of a power plant," he says. "I wanted them to be able to walk past and see a new organism representing a new kind of life."