A ‘passive house’ in the Park Slope neighborhood of Brooklyn, New York. (Cramer Silkworth)

Imagine living in a home so carefully insulated that you almost never have to turn on the heat. During a week in January 2014, during one of the coldest winters on record, the owners of a brownstone in the Park Slope neighborhood of the New York City borough of Brooklyn turned on the heat just once, for about an hour, as the temperature outside dropped close to 0 degrees Fahrenheit. The temperature in the home, however, was in the mid-60s when the owners turned on the heat, and it stayed in the high 60s and low 70s for the rest of the week.

“The house basically functioned in a passive state, even with very rough weather,” says Ken Levenson, president of New York Passive House, speaking at “Housing and Sustainability: A View from Two Continents,” a webinar held by the Urban Land Institute in April. More recently, it was announced that a Cornell Tech facility will be the tallest passive house facility in the world.

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The brownstone had been renovated to meet the Passive House standard, created by the German Passivhaus Institut in the 1990s. Passive House is the latest, toughest standard in sustainable design. Owners and developers around the world have certified Passive House buildings, including U.K. property giant Grosvenor. In the United States, developers are now building hundreds of new units of housing to meet the Passive House standards in states like New York and Pennsylvania.

“Today, it’s really gone global,” says Levenson. Last summer, the first Passive House mid-rise apartment building in the United States—Knickerbocker Commons—opened 24 units of housing in Brooklyn. Passive House developers are also building a 101-unit affordable housing development in the Rockaway neighborhood of the New York City borough of Queens and a 34-unit market-rate project in the Harlem neighborhood of Manhattan.

Developers are likely to start building hundreds of Passive House residential units a year in Pennsylvania. The state’s largest program to build affordable housing now favors applications that meet Passive House standards with an extra ten points out of 130 total possible points in the competition for funding. The Pennsylvania Housing Finance Agency expects to finance 50 developments through the low-income housing tax credit program in 2015. About a third of those winning projects are expected to be Passive House projects—for a total of about 750 new Passive House units from just this year of funding.

Passive House buildings use about 90 percent less energy for heating and cooling and about 75 percent less energy overall compared with conventional construction, according to Levenson. These buildings use so little energy that if they are managed well, they could potentially generate all the energy they need from solar panels on the roof.

Passive measures and components help these buildings use less power; that often starts with excellent thermal insulation. “It’s full of triple-paned windows that are like freezer doors,” says Tim McDonald, president of Philadelphia-based development company Onion Flats LLC and an associate professor of practice at Temple University. Builders also remove “thermal bridges,” which conduct heat into or out of a home. These features can add up to 10 percent to the cost of construction, says McDonald.

“There are very clear absolute standards,” says Levenson. Because of all the insulation, heating and cooling the building should require only 15 kilowatts-hours of energy per square meter per year. The building should also require very little energy from outside: 120 kilowatt-hours or less per square meter per year. “This is the amount of energy produced at the power plant for this building,” he says. “That includes the plug loads, the lighting, the equipment—everything that is going into the building.

“Air tightness is truly fundamental—the tighter, the better,” says Levenson. Sustainability experts test this with a “blower door test,” which involves putting a fan over the door of a home to measure how much air can be pulled out through gaps in the walls and floors. To pass the test, the home should have fewer than 0.6 air changes per hour at 50 pascals of pressure.

Embracing Passivhaus in Europe
The first three private rental apartments to meet the EnerPhit Passivhaus standard opened in February after a rehabilitation by real estate giant Grosvenor Britain & Ireland. The firm, a privately owned property group with 17 offices in 11 countries, will finish another two Passivhaus residential units this fall and has plans to complete more.

“Of 150 to 200 units we retrofit each year, 2 percent will be to the EnerPhit Passivhaus standard,” says Victoria Herring, director of refurbishment and retrofit for Grosvenor’s London Estate, which totals 5,000 properties on 300 acres (121 ha) in the heart of London, mostly in a conservation area.

Grosvenor has already committed to reducing greenhouse gasses by 50 percent at buildings it directly manages by 2023 and by 50 percent at all of its properties by 2030. “Some properties are hard to treat, so they may achieve only a 30 percent reduction,” Herring says. Completing a few units to meet the tougher Passivhaus standard will help Grosvenor meet its broader commitment. “It will help lift our average.”

New regulations also are encouraging Grosvenor to act. In 2018, the United Kingdom’s Energy Act will make it illegal to let or sell a property that does not meet strict energy performance standards. Grosvenor also plans to use sustainable design to help attract residents. “We aim to promote our private rented portfolio as best-in-class,” says Herring. “We’ve marketed these units not just with the energy benefits, but we’ve really highlighted the benefits to health and comfort, like sound insulation.”