One of the top selling points of an all-glass, highrise condo is views, a factor that can be seriously challenged when the highrise is surrounded by other tall buildings. In its design for Aqua—an 823-foot-high, 1.9 million-square-foot tower next to Chicago’s Lake Shore East Park—Studio Gang found an innovative solution to this familiar snag.
The firm extended the floor plates out past the building envelope, creating terraces that open up sightlines around adjacent structures to specific landmarks: Anish Kapoor’s Cloud Gate sculpture, Navy Pier, Lake Street, and more. Rather than plain belts ringing the volume, the architects used the terraces to create an undulating pattern up the facade.
“We first designed a landscape, and then turned it vertical, slicing the contour into 82 different slabs so that there is a transformation over the height of the tower,” said firm principal Jeanne Gang. “The main idea was to create a tall building that people can inhabit on the outside as well as inside.”
In addition to acting as a rather effective view machine, Aqua makes for some intriguing eye candy on the skyline. When viewed from afar, the tower appears slim and rectilinear. Up close, however, the wavy forms of the terraces reveal their depth, and the topographical nature of the elevation becomes apparent. But image isn’t everything that the design delivers. The protruding floor slabs also have an effect on the building’s systems.
The structure—engineered by Magnusson Klemencic Associates—is reinforced concrete, which offers a good deal of rigidity, but at this height and with this use (the building will contain rental apartments and a hotel, as well as the condos), it was assumed that a tuned mass damper would be necessary to combat sway.
However, wind tunnel testing revealed that the terraces, which cantilever as much as 12 feet out from the perimeter columns, cut wind loads enough to ensure stability. “We sensed that the design would reduce the wind, but we didn’t know for sure until getting the modeling done,” said Gang. This buffering effect will also make the terraces hospitable in a city notorious for its windy days.
One unfavorable result of exposing the slabs is that there is no way to create a thermal break, and the floors become conductors that bring unwanted heat or cold to the interior. The sun shading that the terraces create mitigated this negative effect. “When you calculate it out, it ends up being pretty much even,” said Gang. “You lose heat through the winter, but you reduce your A/C throughout the mid season and summer. It’s a wash.”
The architects designed around the microclimates created by the slabs on the facade, specifying five different types of glass depending on the amount of sun each panel would receive. All of the glass is low-e coated, but the material placed behind the terraces is extremely clear, whereas the material in the portions of the facade where the slab does not protrude—areas that the architects call pools—has a very reflective high-performance coating.
The change in glass types has a visual effect, increasing the building’s sculptural depth because the non-reflective panels recede and the reflective panels pop. “We tuned the glass to its environment,” said Gang. “You can see the different shades. It makes a more organic elevation.”