Passive-house architects tend to rely on several basic strategies: Position the building to capture steady southern sun; design a compact shape with a minimal exterior surface area; insulate and seal the whole thing snugly; and install super-efficient windows and ventilation. On the first and second counts, Handel got lucky. The site’s orientation and oblong shape provide a long southern exposure. And because the building is to be divided into 352 apartments, it will have a high ratio of interior to exterior walls.
Insulating and sealing the 285-foot-tall tower will be trickier. “You’re essentially trying to create a cooler out of your building, where the insulation wraps all the way around,” says Lois Arena of Steven Winter Associates, a consultant on the project. The building will have a highly insulated, supertight wrapper ranging from six to 11 inches thick. So that it wouldn’t resemble a bulky coat, the architects angled the wrapper to make it a highlight of the design. It starts on the southern facade, reaches its peak at the southwest corner, then folds all the way around the building and back across the southern facade once more. It will ultimately have an outer coating of metal, with deeply recessed rows of windows creating a series of prominent horizontal bands. At the bottom of the southern facade, the wrapper lifts to form an angular canopy over the building’s main common area.
In conventional apartment buildings, fresh air leaks in through the windows and main walls, while exhaust ventilation pulls air out of the kitchens and bathrooms. But in this airtight building, fresh air will flow through ducts into each of the apartments, and exhaust air will flow out through separate ducts. Up on the roof, two energy-recovery units will extract heat from the exhaust air and transfer it to the incoming fresh air, dramatically reducing the amount of energy needed for heating. On each floor, refrigerant will flow through a condenser on a balcony into the apartments, where residents will be able to adjust temperatures. This kind of system, more common in Europe and Asia, saves energy by operating at a variable, rather than constant, speed.
As the building’s frame goes up, off-site workers are beginning to assemble its walls out of 36-foot-long prefabricated panels—sandwiches of metal, insulation, and triple-glazed windows, with various brackets and clips to hold everything in place. The joints where panels meet one another and the floor present one of the biggest opportunities for heat loss. To head off this risk, the designers devised an intricate system of plastic-membrane flaps and tape to seal the joints. They are teaching their taping method to contractors, one example of how the project aims to serve as a demonstration.
When the residence opens in 2017, it is expected to use just 25 percent as much energy as a typical apartment building of the same size. In the meantime, as local builders, tradespeople, designers, and developers learn more about the passive-house approach, the architects hope it will start to catch on. Gary Handel, the firm’s founding partner, likens the project to a snowplow clearing the road: “It’ll be a lot easier to follow behind,” he says.