The New Passive Houses Are So Energy-Efficient, They Make Heating and Cooling Practically Irrelevant

For Hunter Duplantier, the futuristic-looking house that went up last winter on the edge of the University of Louisiana campus in Lafayette stood out among its traditional-looking neighbors. It’s built like a loft, tall and boxy, with a flat roof and oddly placed narrow windows. But the most unusual attributes of the home were the ones he couldn’t see.

The building is the first in the southern U.S. to achieve official certification as a “passive house.” As such, it needs a mere fraction of the electricity it takes to run a conventional home of comparable size. Once it was completed last spring, Duplantier and two other architecture students enthusiastically volunteered to rent the place and monitor its performance. They moved in during finals week, embarking on an experiment in low-energy living that simultaneously harkens back to the super-insulated-house movement of the ’70s and provides a look at how we all might live in a peak-energy future.

“We were just in awe, just overwhelmed with information at first,” Duplantier says. After spending a record-breaking hot summer there, he reports, the home has “held up pretty well so far.”

The 1,200-square-foot home is one of a growing number of passive houses being built around the country in sizes and architectural styles as varied as the climates where they’re situated. A Maryland developer is putting up a 4,400 square-foot McMansion designed to perform like a passive house but look like an American foursquare, those faux farmhouses popularized a century ago thanks to mail-order construction kits sold in the Sears catalogue. In New York City, meanwhile, another architect has embarked on the first-ever passive retrofit of a genuine century-old townhouse.

“It was a challenge,” says Jeremy Shannon, the vice president of Prospect Architecture, P.C., who convinced a couple of Brooklyn homeowners to go passive instead of doing a run-of-the-mill retrofit of their Park Slope brownstone. “We both agreed,” he says of the owners, who want to remain anonymous, “This is going to be a real extreme challenge. Let’s see if we can do it.’”

A Passive Home Primer

Conventional buildings lose inside heat and air-conditioned air via ill-fitting windows and doors and allow outdoor temperatures to seep inside through leaky walls, ceilings and floors. That ratchets up a home’s carbon footprint—and the household energy bills. Builders typically use insulation and tighter-fitting windows to cut down on such air leakage, and increasingly employ one or more of the much ballyhooed stars of today’s rapidly growing U.S. green building marketplace: solar panels, geothermal heating systems, windmills and other so-called “green bling” that reduce a house’s carbon footprint by generating homemade renewable energy.

A passive house offers a different approach—and philosophy—about how to achieve the same low-carbon lifestyle. Instead of reducing emissions by generating alternative power, these buildings simply don’t require much electricity. They are so airtight that it takes little more than the inhabitants’ body heat to warm them up in cold climates, while in hot ones like Louisiana, the emphasis is on not letting the sticky outside air permeate the building’s “envelope,” industry parlance for the four walls, roof and ceiling.

Considering that nearly half of U.S. greenhouse gas emissions come from our homes (48%, to be exact, according the U.S. Energy Information Administration), and that roughly half of the nation’s electricity comes from dirty coal-fired power plants, the passive house building system is a major step forward in the fight against global warming. A certified passive house uses about 90% less energy for heating and cooling than the average home, reducing total energy consumption to between 60% and 70% less than a conventional home, according to the Passive House Institute U.S., an Illinois-based nonprofit group that promotes the building system and certifies U.S. buildings.

“It’s the most aggressive standard in the world for energy efficiency,” says California builder Rick Milburn, contrasting it with U.S. initiatives such as the federal Energy Star program, which requires buildings to perform just 15% more efficiently than conventional homes built to the 2004 International Residential Code.

“It’s a serious commitment,” agrees University of Louisiana Professor Corey Saft, who built the house where Duplantier lives. “You have to be really clear that it’s what you want.” The commitment begins before the foundation is poured, which, for starters, must be sealed off and insulated from the ground below.

Saft says he spent about 30% more on insulation than he would have in a standard construction project but saved on the passive home’s heating and cooling system, which is smaller and less costly than ones used in conventional homes. These houses are so tightly wrapped that they conserve indoor temperatures much better, which means equipment doesn’t have to work as hard to maintain a constant, comfortable environment.

Instead of the standard central air or furnace, the key component of a passive house is its heat-recovery system. As the name implies, heat from the home’s outgoing polluted air is captured via a heat exchanger inside the home’s ventilation units; incoming air is warmed by this exchanger as it enters. The home’s heat is preserved, while still allowing a constant circulation of fresh outdoor air for improved indoor air quality. In parts of the U.S. where cooling and dehumidifying are as much of a challenge as heating, Energy Recovery Ventilators, or ERVs, are being used. Unlike straight heat-exchangers, ERVs also transfer water vapor, which prevents the air from drying out in winter months, and removes indoor humidity during summer months. ERVs allow for one-third of the building’s air to be replaced with fresh air every hour.

Passive house proponents rave not only about the energy savings but also about the fresh air and quietude. “As soon as the windows went in, the house became warm and quiet and peaceful,” says Catherine O’Neill, whose new home in Sonoma, California, built by Milburn, became the first in that state to earn passive house certification earlier this year. She says what really impressed her was that the entire mechanical system fits into a space that she thought would be her linen closet.

Katrin Klingenberg, executive director of the Passive House Institute U.S., who built the first U.S. passive house in 2003 and has lived in it ever since, says her electric bills come to just $25 a month in the summer and $60 to $94 a month in the winter at her 1,000-square-foot home in Urbana, Illinois.

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