Architect Jeanne Gang of Studio Gang had something else in mind when designing the mixed-use project, which contains apartments, condos, a hotel, offices, retail, and parking.
Gang saw an opportunity to create what she describes as vertical topography — a contour of gentle hills and valleys on all four sides of the tower that would provide the building's occupants with vantage points for views of the surrounding city.
Contour models are usually built up with horizontal layers of cardboard to define the high points, but in the case of Aqua, the contours are sliced vertically instead of horizontally.
Designing with Desire Lines
Located a block northeast of Chicago's Millennium Park, at the corner of Upper North Columbus Drive and Wacker Drive, Aqua Tower is part of Lakeshore East, a large, multi-block brownfield development planned by SOM for a 28-acre (11-hectare) site in the former Illinois Central Railroad yards. The 82-story tower sits on a large podium that holds an extensive roof garden, along with a pool, running track, and other amenities. Aqua is also surrounded by other towers.
Gang and her design team built a large model of the neighborhood surrounding the site, inserted a schematic tower, and then ran "desire lines" from the tower to the view targets, such as Lake Michigan, Frank Gehry's Pritzker Pavilion in Millennium Park, and the BP Pedestrian Bridge, also by Gehry.
Gang likens this process and the resultant view diagram to maps of ski routes that show the start of the slope and the finish line at the bottom.
The design of Aqua involved the creation of "hills" on the facade, formed by series of balconies sized and shaped to allow views around the corners of the tower and through gaps between existing buildings. The south facade's higher contours provide additional shading to reduce solar gain in summer. The facade's "valleys," meanwhile, admit more sunlight to interior spaces of the tower.
Studio Gang also used different kinds of glass on different facades and in different areas of the facade, depending on orientation and the varying depths of balconies. All of the glazing is low-e. On the east and south facades, the glazing is reflective in areas without a balcony, to provide shading.
On the west, the glass is tinted to improve its shading coefficient. Six different types of glass were used on Aqua Tower — clear, tinted, reflective, spandrel, translucent, and fritted — depending on the orientation and the function of the interior space behind the glass.
Such features contribute to the energy-efficiency of the project, for which LEED certification is sought.
An added benefit of the variegated facade is dissipation of wind loads, to the extent that the tower did not require a tuned mass damper, often used in high-rises to counter wind forces.
Balconies with Curves
Part of Aqua's aesthetic appeal are the elegant, sparely detailed floor slabs that give the building its eye-catching identity. About 90 percent of the residential units have accessible balconies; the remainder either do not have balconies or the slab projections are too shallow to be accessible.
The undulating balconies are not attachments to the structure, as they are in most tall buildings, but are actually extensions of the poured-in-place floor slabs, each one unique. The deepest balconies are 12 feet (3.7 meters), while the narrowest are only five feet (1.5 meters).
The slabs taper from nine inches (23 centimeters) thick at the window wall to six inches (15 centimeters) at the edge of the slab, giving the balconies their crisp profile.
Each concrete slab has an impervious coating on the top to keep moisture from penetrating the slab, and a pervious coating on the underside to permit moisture to emit. The light-colored coatings help reflect daylight into the interior, and effectively render artificial light, such as the colored LED lights that trim the balcony edges and wash the tower in broad swatches of color at night.
Even though each floor has a different profile, Gang says that her firm's close collaboration with the general contractor and the concrete subcontractor early in the project resulted in a coordinated effort that allowed a floor to be poured and finished every three days during construction.
If you fixate on the visual aspect of Aqua's undulating balconies and undulating forms, you might miss one of Studio Gang's deeper design goals — to populate the facade.
In most residential buildings, balconies are included largely for the purpose of real-estate marketing, but they often don't function as one might expect, becoming outdoor closets for apartment-dwellers, and standing empty at many hotels that limit balcony access.
Studio Gang intends for Aqua's balconies to be fully occupied, and the generous balcony areas make this a reasonable possibility.
Aqua Tower creates an arresting visual effect on the skyline. But perhaps its larger achievement is the creation of a vertical landscape, allowing high-rise dwellers to enjoy glimpses of Chicago landmarks and distant vistas from its hills and valleys in the sky.
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Michael J. Crosbie is editor-in-chief of Faith & Form, the chair of the University of Hartford's Department of Architecture, and a contributing editor to ArchitectureWeek. More by Michael J. Crosbie