Living in a Thermos

Ninety-six St. Marks Avenue looks like an utterly ordinary Brooklyn apartment building. Crimson brick front, fire escape, about 80 years old. It’s under heavy renovation right now, a commonplace sight in Prospect Heights, where lots of older buildings are being spiffed up by new owners. What is anything but typical, though, is its future bill from National Grid. When the rehab is finished, it’ll use 60 to 70 percent less energy than comparable buildings, and 90 percent less heat.

It’s what is called a “passive house,” almost a misnomer for a home that’s built to be actively, aggressively energy-efficient. The walls are hyperinsulated, the windows are triple-glazed, and the whole building is engineered airtight. “Basically, you’re building a thermos,” says Mike Knezovich of the Passive House Institute US, a nonprofit association that certifies houses meeting the standard. (The concept originated in Germany and has taken off in northern Europe.) Chunky “thermal mass” items, like stone-slab floors and mantelpieces, are meant to soak up and hold heat. Ventilators pump stale air out and bring fresh air in—keeping it cool or warm as necessary while filtering the atmosphere. During the winter, a significant bit of the household’s heat comes from the residents’ own bodies and their appliances.

This is all a different shade of green from LEED designation, the ratings by which most ecofriendly projects in the city are judged. “It’s not about solar panels and bells and whistles,” says 96 St. Marks’ architect, Ken Levenson. “It’s about optimizing what needs to be built.” About fifteen such projects are planned or under way in New York, says Andreas Benzing of New York Passive House, a nonprofit group that promotes the technology. (The 96 St. Marks building is in the running to be the first multifamily house to be certified, though which one actually gets the designation depends on the contractors.) A mixed-use structure at 174 Grand Street in Williamsburg is on its way; its architects at the firm Loadingdock5 say they’re doing more work around the doors and windows before submitting it for approval. A single-family house in Brooklyn Heights is almost done, too. In 2009, only a handful of New York architects were trained in passive-house design, says Benzing; now there are about 50. “We’re not talking about fluff,” adds Brendan Aguayo, co-developer of 96 St. Marks. “This really has an impact.”

It can be a headache to build this way. Budgets for passive projects can run up to 10 percent more than typical buildings, a potential turnoff for developers. (They’ll eventually pay for themselves in reduced energy costs, of course, though the home­owner rather than the developer will reap those benefits.) Windows are often from foreign manufacturers familiar with the requirements. Contractors must build exactly to specs. Homeowners and developers need architects who can deal with all the rules. And one requirement for certification is passing a third-party “blower door test,” in which a big fan pressurizes the house to see how leaky it is—meaning that you don’t really know if you’re successful till you’re almost done. The standards are harder to apply in conversions of old buildings, where curveballs like leaky corners are harder to avoid. “When you’re doing a reno, it’s sort of more experimental,” says Aguayo.

Still, it may all pay off. “People look at [passive house-building] as a complication in an already tough business,” says Knezovich. “Once they understand it, they can sell it.”

Living in a Thermos