“Who wouldn’t want to work on a Bunshaft building?” asks architect Rod Kruse, a principal at BNIM. The rhetorical question is Kruse’s way of explaining why he was so pleased that insurance provider American Enterprise Group (AEG) chose his firm to renovate its headquarters in downtown Des Moines. The 153,000-square-foot office building, completed in 1965 and designed by renowned Skidmore, Owings & Merrill (SOM) partner Gordon Bunshaft, was highly unusual for its time. Built for American Republic Insurance (now an AEG subsidiary), the eight-story edifice has minimal internal structure, being supported almost entirely by its east and west poured-in-place concrete walls that are lifted above the ground plane on giant steel “knuckles.”

This configuration creates a strong, stark form. But the scheme also allowed a 90-foot clear span that, in turn, provided an open, flexible workspace, anticipating current office design trends. And with private offices placed around the core, it gave workers daylight and views through the unobstructed north and south glazed elevations.

Over the years, the owners had made some changes, such as substituting cubicles surrounded by tall partitions for the original open work-area desks, but they had, for the most part, maintained the building’s defining characteristics. However, by the time the structure approached the half-century mark, the interior finishes were badly deteriorated and its mechanical systems were outmoded, making it impossible to maintain comfortable temperatures. The joke among employees was that they could experience all four seasons in one day without ever going outside, says the AEG executive who oversaw the renovation, Medha Johnson, vice president for human resources.

The revitalization project, completed last August, remedied the situation with state-of-the-art systems as well as improvements to the building envelope, including replacing the original single glazing with insulated glazing. The architects designed the new mullions so they appear identical to the originals on the exterior. BNIM estimates that such changes will save the client $2 million each year in energy and maintenance costs. The building’s new plumbing has already saved AEG a considerable sum, having reduced the water bill from $22,000 to $5,000 per month, says Johnson.

Updating the infrastructure could have compromised such hallmark features as the ceilings of precast concrete Ts. Here SOM had ingeniously integrated ductwork and lighting to make a series of illuminated coffers. The renovation team recreated the effect with LEDs, but also invisibly incorporated sprinklers and cables for data. BNIM’s trick was to reconstruct the cylindrical ducts with a slightly chamfered top, creating a spot to conceal the new equipment.

Replacement of the systems required significant interior demolition. Afterward, contractors meticulously rebuilt walls and applied finishes. The renovation team also restored or replaced many of the original furnishings, which had been selected or custom designed by SOM—but now AEG employees who occupy the open office areas have BNIM-designed ergonomic work­stations with sit-stand desks. In keeping with Bunshaft’s concept, these have low dividers so as not to impede the daylight and views.

Since the renovation, the building has been listed on the National Register of Historic Places—a testament to how faithful the project team was to the original. This status allowed AEG to take advantage of state and federal preservation funds. The grants, along with other sources, including a local jobs incentive and state economic development tax credits, paid for half the $30 million construction cost.

Johnson guesses that AEG could have built a new headquarters for $15 million, “though it would have been obsolete in 10 or 15 years,” she says. Instead, the renovation has given Bunshaft’s building another five decades, according to Kruse’s estimates. His hope is that BNIM’s interventions are nearly imperceptible. If he’s done his job right, he says, “most people won’t even realize we’ve been here.”  

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