Most buildings that meet the rigorous passive house standards are single-family homes. But a new passive house apartment building in New York City will be 26 stories high—the tallest and largest in the world.
Passive homes are ultra-low energy buildings that require little heating or cooling. To meet the requirements, a building must use 60% to 90% less energy than a normal efficient building of the same size, which means building an almost impenetrable envelope around the outside.
"It's been an exploratory process for us, partly because nobody has done anything of this scale," says Blake Middleton, partner at Handel Architects, the firm that designed the building for Cornell Tech's new campus on New York's Roosevelt Island. "There are a good number of low-rise passive house buildings in Europe and a lot of freestanding houses. But when you get into something that's 10, 20, or in this case almost 30 stories tall, it's a whole different ballgame in terms of how you put it all together."
"If you wrap the building up really tight and you seal it really well, the amount of energy required to heat or cool is drastically reduced," Middleton says. "You basically only need to provide little bursts of heat."
But getting a tight seal means incredibly detailed work in construction, something that's harder to do the bigger a building gets. It also means doing pressure tests—to see if air is escaping in or out—something that's also hard to do on a 270,000-square-foot high-rise.
"With a 4,000-square-foot house, it's one thing to seal up all the windows and doors, stop up the gaps, and turn on the pressurization and see if you've accomplished that," says Middleton. "You can find relatively quickly and easily where any of the small leaks might still be there, track those down, and seal those up and pretty quickly get it to meet that performance requirement. The problem is doing that on 26 stories all at one time."
Middleton admits that the team is still figuring out exactly how to accomplish that. But when they do, it will make it much easier for other high-rises to follow. "We're really excited about figuring out how to solve those issues," he says. "We're beta testing this, nobody's done it before."
The building is also much cheaper to build than the next-largest passive house high-rise, a slick 20-story office building in Vienna covered in glass. "Cornell's primary objective was to provide comfortable and affordable graduate and post graduate student housing, with an emphasis on affordable," he says. "We had to look very quickly to what was going to be a system of enclosure that would try to meet that affordable target."
The biggest cost in exterior walls is usually windows, so the designers made them big enough to give the right amount of natural light (and river views), but not as big as you'd see in a typical luxury condo building. The designers also used pre-fab walls (extra thick, at 14 inches) that are sealed in the factory, so there's less work to do on site.
"If we can discover ways to do the installations really efficiently and accurately, that will begin to drive costs down," Middleton says. "When we complete this, I think it's going to begin to take the fear factor, the uncertainty, out of this process. The next one will be even less expensive."
The team also pioneered some new solutions to meet the building code. The building's ultra-tight seal means that they have to add special ventilation systems for efficiently bringing in fresh air—and they had to convince the city to allow something different.
"It significantly reduced the number of fans and other equipment we needed," he says. "It will be interesting to see if the city begins accepting the logic of that concept, and whether that might have an influence on future mechanical systems for apartment buildings in New York."
There's technically no limit to how big a passive building could be, Middleton says. And as building standards shift to require more efficiency, we could soon see more high-rises inspired by this one.