Curves Over Chicago: Aqua, a new 82-story residential tower and hotel near Lake Michigan, adds a new dynamism to the city’s skyline.
Jeanne Gang, FAIA, of Studio Gang, had not designed a high-rise structure (not to mention a sustainable one) before Aqua, the 82-story tower in Chicago’s downtown. Her small 38-person firm, in business in the city since 1997, had, however, distinguished itself with community centers, schools, and houses. Then in 2004 she met developer and architect James Loewenberg of the Magellan Development Group, who is behind the 28-acre Lakeshore East mixed-use complex, which has been under construction on the old Illinois Central Railroad yards along Lake Michigan during much of the last decade.
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Loewenberg asked Gang to come up with a fresh design for a new 1.9 million-square-foot structure in Lakeshore East, for which he would be both the client and the executive architect. Now the $300-million (construction) residential tower, which rises from a podium on the 179,946-square-foot site near Millennium Park, has just been completed. In a city known for its rectilinear Miesian skyscrapers, Gang brought back the curve by wrapping her residential tower with sinuously swerving concrete balconies. Preceding Aqua in its curvilinearity are the iconic twin cylinders of Marina City that Bertrand Goldberg designed in 1964. But his floor plans, consistent with the round shape, forced occupants to fit right-angled furniture into wedge-shaped rooms. In the case of Aqua, Loewenberg opted for a rectilinear plan in the reinforced concrete structure, with floors 4 to 18 reserved for a hotel with 225 rooms, floors 19 to 52 dedicated to 474 rental apartments, and the remaining upper floors devoted to 264 condominiums. Penthouses occupy the 80th and 81st floors.
Gang figured out how to give the envelope its swirling architectonic form while working with the building’s rectangular footprint. At the same time, she devised ways it could be energy efficient through sustainable strategies that have enabled the developer to apply for LEED status. Loewenberg admits green wasn’t totally on his mind at the beginning of the process, but because of Chicago’s strong environmental laws, his company was already inserting as few caissons as possible in the brownfield site so that less special waste had to be removed. He soon thought, “We could make this building green. We were already doing one and didn’t even know it.” Gang, who has incorporated energy-saving features in a number of her projects, was delighted.
The marketability of green features obviously proved enticing. For example, curving balconies shield apartments from intense sunlight while adding private outdoor space. Various types of high-performance glazing on the exterior also help cut solar load while taking advantage of the views. And an 80,000-square-foot planted garden on the tower’s three-story podium provides a park that diminishes the heat-island effect. To top that, Magellan is offering the first electric-vehicle charging station open to the public in the city in Aqua’s underground garage. Gang observes, “Loewenberg likes the competitive aspect of trying to be greener than other developers.”
Needless to say, carrying out the design was tricky. The sinuously curved concrete decks on each floor assume different configurations where balconies extend anywhere from 2 to 12 feet. Although the architects used computer modeling to create the rippling contours, the fact that each floor slab is unique in shape meant calculations had to be done separately for each floor. (Interestingly, Magellan could reuse an edge-form steel plate to guide the concrete pour: The steel form would bend for a pour and then spring back into a straight line, ready to be bent again for another curve. “We didn’t waste six miles of formwork that couldn’t be reused,” says Loewenberg.)
The 9-inch-thick balcony slabs thin out as they extend from the cladding line to the edge of the cantilever. This profile helps in drainage, notes structural engineer, David Eckmann of Magnusson Klemencic in Chicago, and keeps rainwater off the face of the building. The thin concrete slabs do tend to lose heat in the winter, Gang acknowledges. The architects and their consultants investigated adding thermal breaks between the indoor and outdoor concrete slabs, but this strategy proved too difficult to achieve for this project. Gang maintains, however, that in terms of overall energy use, the heat loss in the winter is offset by savings in air-cooling in the summer owing to the concrete canopies, the glazing, and the natural ventilation.
While the concrete decks cut solar load on the glass facades, the architects left certain glazed areas exposed—oblong expanses they call “pools”—for interiors where balconies aren’t needed but direct sunlight is welcome. To reduce solar load on the exposed glass, Studio Gang conducted sun pattern studies that in turn led to its specifying six different types of glazing. In addition to low-E coatings, the firm selected reflective glass for the exposed parts of the east and south facades. Similarly, tinted coatings for glass on the west facade improve the shading coefficient. In addition, much of the exposed glass is fritted, not only to help reduce heat and glare, but, along with dark gray aluminum balustrades, to keep birds from crashing into the tower. Already this strategy won Aqua a Proggy award (named for “progress”) from the People for the Ethical Treatment of Animals.
Inside the dwelling units, the architects selected materials and equipment with sustainable features such as renewable and recyclable bamboo for the floors, plumbing fixtures including toilets, faucets, and showerheads that cut down on water use, plus Energy Star-rated appliances.
At the base of the tower, a three-story podium contains the hotel and apartment lobbies, the hotel ballroom, and other public rooms. But the coup de théatre is the 80,000-square-foot podium roof garden, with an outdoor swimming pool and a running track. In this park-like roof, meandering paths weave between low evergreen plants and deciduous plantings that may not be native but generate a “geometric naturalism,” says Ted Wolff, of Wolff Landscape Architecture in Chicago. Instead of nourishing the plants with collected rainwater, Wolff put in place a drip irrigation system to efficiently use potable water. In addition, a continuous drainage layer allows water to flow under soil, gravel, and concrete walls to drains and pipes. The roof’s vegetation is not only aesthetic but also combats the heat- island effect during the hot summer months by lowering ambient temperatures around the building.
The tower, with its entrance off Upper Columbus Drive on the west, is designed so that the podium’s park overlooks the Lakeshore East development on the opposite side. Since the grade drops 50 feet to the large Harbor Park forming the centerpiece of the complex, Gang designed two concrete stairs—one is a switch-back stair; the other a spiral—to take pedestrians down to the grassy lawn. Nine townhouses, also designed by the firm and tucked below the podium, face east onto the park, while underground parking fills out the rest of the space. Here a six-charger station can accommodate 24 plug-in electric and hybrid gas-and-electric two- and four-wheel vehicles.
Because Aqua “fosters a sense of urbanity and a related life style,” says Loewenberg, it contributes to sustainabiity. The tower appeals to youngish working people who prefer its light, airy apartments with balconies and views, where they can take an elevator for a run or walk in the roof park, or a swim in the outdoor pool. Small wonder that WalkScore.com gave Aqua a “Walkers’ Paradise” rating of 100.