Chicago-based architecture firm Krueck + Sexton Architects has designed an undulating, reflective tower and podium for 130 North Franklin Street in downtown Chicago. © Krueck + Sexton Architects
A new tower and podium that will be defined by open spaces and undulating facade will occupy half a city block in downtown Chicago.
May 28, 2013—Chicago takes architecture very seriously. So it was with great deliberation that the Chicago-based architecture firm Krueck + Sexton designed an undulating, reflective tower and podium for 130 North Franklin Street, which will join such notable buildings in the city as the Willis Tower, located less than half a mile away. The new design includes a highly engineered, high-performance facade system that despite its seeming complexity will be affordable and easy to install.
The 68,000 sq ft site for the new structure encompasses half of an entire block, an unusual situation in a city as densely built as Chicago, according to Mark P. Sexton, FAIA, LEED AP, an architect and a founding principal of Krueck + Sexton and the principal in charge of the design.
The 1.2 million sq ft structure will include a 48-story office tower and a 7-story attached podium; the podium will offer 13,000 sq ft of ground-level retail space and three levels of parking that will serve 200 cars, plus two levels of office space that will continue from the podium into the office tower, offering 45,000 sq ft floor plates and 18 ft floor-to-floor heights. A so-called sky park atop the podium will feature a two-story atrium that will allow natural light to reach the office space on the podium’s expansive top floors.
Open space is key to the public face of the building as well. The design includes two generous ground-level public plazas that will serve to open up the block, according to Sexton. “The idea is we really want the street and the pedestrian experience to be open and light filled,” Sexton says. A 50 ft high glass-enclosed lobby with multiple entrances will welcome visitors to the building, continuing the sense of openness and exposure that the plazas will create.
The tower will feature a concrete core and steel beams that create clear spans with column-free corners. Twenty-one high-speed elevators will serve the building: eight for the low-rise sections of the building, seven for the mid-rise sections, and six for the high-rise sections.
To maximize the opportunities for views of the city, the tower will increase in floor space as it rises above its neighbors, according to Sexton. “Each floor plate is different because the building undulates a bit as it folds,” he says. At the mid-rise point, the floor plates are approximately 25,000 to 26,000 sq ft, and the space increases to 27,000 sq ft in the high-rise portion of the building. This increase in floor space derives partly from to the smaller size of the concrete core in the upper stories of the tower and partly from the fact that the tower has been designed to be slightly wider at its top than at its base, Sexton says.
A so-called “sky park” will be located atop the complex’s
seven-story podium; a two-story atrium that will channel natural
light into the office space. © Krueck + Sexton Architects
The tower will be clad in a unique high-performance skin, according to Sexton. The facade “will be a unitized wall, which means that everything is made in the factory and brought out so that it is basically clipped together,” he says. “We’ve developed some very sophisticated details of how you actually fold a curtain wall like this and still make it part of a whole system.” The skin represents an evolution in a system that the firm has used on other projects. This iteration will include modules measuring 5 ft by 13 ft 6 in. with internal aluminum members placed in such a way that the facade can be “folded” around floor plates of different sizes.
The building “ripples on the inside” as well, Sexton says. “What you see on the outside, the subtle folding and movement of the perimeter, actually telegraphs to the inside.” This was done, he explains, to provide multiple experiences not just for the public as they view the building but also for the occupants working within. “We’ve tried to get a little bit more expression, both for the public—because all of a sudden that facade will shimmer and become more crystalline—and, maybe more importantly, [for] the user on the inside,” he says. The form gives the building occupants “a variety of views,” he adds. “It won’t be just one flat wall looking east, north, west, and south.”
The cladding will be inserted piece by piece from inside the building, a benefit in an urban setting with the infamous climatic variability and windiness of Chicago. “You start from the bottom of the building and work up, and . . . [the modules] clip in so that all the gasketing and what have you is not done through sealants; it’s all done through physical connections, which means that it’s extremely air- and watertight,” Sexton says. “It is highly engineered and highly produced, so that it clips in [almost] the way a LEGO block would almost click in.”
The New York City–based developer of the site, Tishman Speyer, is dedicated to sustainable design, and the design team is hoping the project will qualify for gold certification in the U.S. Green Building Council’s Leadership in Energy and Environmental Design program. The facade is the first step in accomplishing that goal, according to Sexton.