Just Add Body Heat 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

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The first passive house in the South, located in steamy Lafayette, Louisiana. © Corey SAFT

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.

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An energy-efficient heat-recovery system delivers fresh air. © Adam Bell

“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.

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A new passive home in Sonoma, California, has impressed owner Catherine O”Neill with its quiet, warmth and low maintenance. © O’Neill House Photos: Ned Bonzi

Living on the Cheap

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.

Duplantier says that he and his roommates also paid just $25 a month for electricity over the summer to supplement the energy generated by the home’s 3.264-kilowatt rooftop thin-film solar photovoltaic system. Solar panels aren’t a given in passive homes, but many projects include them since it takes far fewer solar panels to slash a passive house’s carbon emissions to zero than would be needed for a conventional home. Duplantier expects to pay little o

r nothing for electricity during cooler months when he and his roommates can throw open the windows and turn off the A/C.

In larger homes, the expected savings can be eye-popping. Architect David Peabody, who is building a passive home called “The New American Foursquare” in Maryland, has calculated that it will take about $700 a year to heat and cool its 4,400 square feet, compared to about $7,000 for a conventional home of comparable size in that zip code.

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O’Neill house interior

Peabody thinks passive houses are better positioned to enter the mainstream than those “blingier” green homes because they repurpose commonly used equipment instead of requiring builders to learn a whole new skill set like how to install solar panels or radiant heating systems that could saddle homeowners with maintenance nightmares. “There’s nothing unusual about an ERV,” he says, noting that the devices are often used in hospitals and office buildings. “What is unusual is you are using it for your heating and cooling and to divert that throughout the house. Our whole approach in this house is to keep things simple, so it’s not a lot of maintenance or a lot of unusual gadgets,” he says. “It’s not a “Look at me!” “Gee whiz!” type of house.”

Passive is not only for Houses

Pioneered over the last two decades in Germany, a passive house, known there as passivhaus, doesn’t have to be a house at all. In Europe, more than 15,000 homes, schools, hospitals and apartment and office buildings have been built to this standard, and passive design has entered local and regional building codes much in the way the U.S. Green Building Council’s (USGBC”s) Leadership in Energy and Environmental Design (LEED) has in this country. And beginning in 2020, the European Union will require new buildings to produce nearly all the energy they consume, a sea change that is expected to fuel even more passive house growth abroad.

It’s hard to make an even comparison between LEED and passive houses. LEED takes a more holistic approach to green building—from how and where raw materials are produced to finishing touches such as bike racks. Builders are allotted points for everything from solar panels to water-saving installments to Energy Star kitchen appliances. Accumulate enough points and your building qualifies for certification. Passive house certification operates on a pass/fail basis. Before certification, each building must pass a blower door test, in which a fan is used to suck all the air out of the house to check for air leakages. To gain certification, buildings must be airtight, meet rigid heat recovery standards and use minimal energy. Extra bike racks or energy-efficient appliances won’t make a difference.

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The Hudson Valley Passive Project resembles a modern barn. © Dennis Wedlick Architect LLC.

Still, Klingenberg says, “LEED and passive house [standards] are beautifully compatible.” Her institute is lobbying for the USGBC to adopt passive house as its energy standard. Such a move, she suggests, could resolve the public relations problems the organization has faced in recent years when LEED certified buildings have failed to deliver on their promised energy savings.

The building system is the brainchild of a German architect named Wolfgang Feist, PhD, who founded the Passivhaus Institut in Darmstadt, Germany, in 1996. Feist has said that he took his inspiration from Amory Lovins of the Rocky Mountain Institute, who was among the builders of the first generation of super-insulated houses in the 1970s.

Those earlier experiments fizzled out, perhaps due to problems with water condensation, mold and poor air quality that arose precisely because they were so tightly built. Feist addressed those concerns with design improvements and the addition of heat-recovery devices such as the ERVs.

It has taken a while for Feist’s inspiration to make it back across the Atlantic. Even after the first passive house went up in 2003, the design was slow to catch on. But that may be changing. Since the Passive House Institute U.S. opened its doors in 2008, operating on a license granted by the German institute, it has certified more than a dozen buildings and several others are under construction, Klingenberg says.

Adopting the Passive Lifestyle

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A passive retrofit is being attempted on a Brooklyn townhouse. © Adam Bell

Perhaps one of the reasons it has taken so long for passive house design to establish itself in the U.S. is the wide array of climates, each requiring specific building modifications. The original German system, in contrast, is concerned mainly with heating.

Passive house projects in places such as Maine and the Midwest largely follow the German approach without much modification, builders say. Skipping the air conditioning was not an option in Louisiana, however. And, in Southwestern states like New Mexico, a passive house design must take into account dramatic daily temperature swings.

To meet the cooling and dehumidifying needs in Louisiana, Saft installed a one-​​ton mini ​​split (small, ductless and easy-to-install) air-​​conditioning system coupled with an ERV, as well as a device called a back-vented rain screen, which serves the dual purpose of shading the building and allowing rainwater and condensation to escape outside and evaporate.

In Bethesda, Maryland, a D.C. suburb with hot, muggy summers and cold winters, Peabody installed an ERV and mini splits in the basement and attic. Those units will be attached to ducts to pipe cool air or heat throughout his so-called “New American Foursquare” when needed. But that’s just the backup system. The five-bedroom house will have a “ground loop,” a coil of tubing under the foundation that will heat incoming air in winter and cool it in summer before it enters the ERV. During colder months, heat will also be generated by coils linked to the hot water heater, an operation that requires about as much electricity as a hair dryer.

The weather is just one of the idiosyncrasies of place that architects must deal with. Shannon, whose business involves performing a fair amount of retrofits, wrestled with how to insulate the hatch area leading into the basement of a century-old New York City townhouse. In the end, he installed a door in the cellar wall and laid down three inches of closed-cell insulation between the door and hatch. Still, as of September, the townhouse hadn’t passed the blower door test. New buildings minimize such challenges. With the Hudson Valley Passive Project, architect Dennis Wedlick is building a passive house in Claverack, New York, that resembles a modern stone barn, featuring a wall of glass and a pine-beam arch.

The Cost of Passive Construction

Like other green buildings, passive houses are more expensive to construct than conventional homes. Klingenberg’s institute estimates about a 10% price premium, though builders say the learning curve can raise costs by up to 25%. But they expect that to drop as architects, developers and subcontractors gain experience.

“The cheapest solution is clever and thoughtful design,” says Brian Uher, co-owner of Amicus Consulting Services in Kensington, Maryland, who is one of a growing number of construction industry professionals to receive training and certification as a passive house consultant.Milburn, the California developer, says he’s “had to go back to school in a couple of ways’ to learn the passive house system, but adds: “T

hose are good problems to have.” As an industry, he says, “We’ve been asked to build cheaper and cheaper and our workforce has become less detail-oriented. We need to relearn how to build buildings.”