Novel double-stair core saves precious space for Libeskind condominium tower

October 01, 2006 |

The sleek 38-story Aura Condominium tower designed by Studio Daniel Libeskind in association with Stantec Architects will do more than change the Sacramento, Calif., skyline. The $124.5 million building's innovative structural core and central staircase design is the first of its kind to be approved in California, and could significantly influence future projects.

The architects, with Schirmer Engineers of Las Vegas and Buhler & Buhler Structural Engineers of Sacramento, designed a connected but separate double-stair exit system that's divided down the center by a four-hour concrete fire wall and, along with the building's three elevator shafts, is encased within a central core constructed of 30-inch-thick concrete walls. The elevator lobby, shafts, and corridor connecting the stairs are individually pressured to control smoke.

“Traditionally, exit stairs have to be separated by a set minimum distance and the travel distance between the two stairs has to also be separated by a set distance,” says Rick Harper, AIA, managing principal at Stantec, Sacramento. “For this tower, we met code for separation travel distance, but intertwining the stairs took some time to get approved.”

The core and stair design met International Building Code, but since California hasn't yet adopted that code, the approval process consisted of meetings and then more meetings with building officials and the fire marshal. “We expressed to them that we were going to do this and we had something where the end result would be as safe or safer than the standard, existing double-stair exiting system,” says Harper.

The architects lobbied hard for the central core and stair design because it dramatically increased the building's usable square footage. “The floor plates are fairly small, around 9,000 square feet,” says Harper. “Having two completely separate stairs in a 9,000-square-foot plate eats up a lot of usable floor area, but pulling them together saved a lot of space.” The architects were able to squeeze approximately 200 units into the 420,000-sf building, which also has ground-floor retail space and a five-level parking garage.

Currently in final review stages, the building should break ground by the end of October.

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