How a new kind of home which produces more energy than it consumes, can drastically reduce fuel bills and CO2 emissions.

Ursula Sautter | June/July 2009 issue

Governments around the world are scrambling to address the twin crises of our times—the recession and climate change—by investing in infrastructure and green energy projects. The Obama administration’s stimulus package, for example, contains billions in incentives for alternative power sources and energy-efficiency increases affecting millions of homes. The question is how to identify “shovel-ready” projects that can quickly deliver the economic boost and CO2 reductions we so urgently need. Rolf Disch, an architect and environmentalist in Freiburg, Germany, has an answer: houses that produce more energy than they consume.
“What if each house became a power plant, if it created even more energy than it used internally?” Disch, 65, first asked himself 15 years ago. To design that home, he built on the ideas of the “passive house” movement that started in Europe in the early 1990s. Instead of relying on the electricity grid for power, a passive house taps available energy sources—sunlight, the body heat of occupants, even the thermal gains created by ordinary domestic activities such as cooking, bathing and using electrical appliances. The building is well-insulated and airtight so it retains most of this energy and, through highly efficient heat-exchange ventilation technology, uses it to cool itself in summer and heat itself in winter. The houses are called “passive” because most of the power consumed is collected from ambient energy in the environment. When extra juice is needed, renewable power units supply it, like the solar array on the roof of the residential and commercial complex Disch built in Freiburg in 2004.
“I only ever had to switch on the heating once,” says Stefan Sattler, a 32-year-old lawyer who has rented a penthouse in the Disch-designed complex since October of 2007. Even then, Sattler only needed the extra heat—purchased from the local heating grid—for two or three hours. Since he and his fellow residents sell the surplus energy produced by the building’s solar panels back to the city’s utility provider at a profit, Sattler is one of the few people who opens his utility bills with real glee. He’s earning money from solar power rather than paying for oil or gas. The average unit in the Freiburg complex earns $5,075 a year this way instead of spending $4,625.
Passive homes can save consumers a bundle in fuel bills—and the planet even more in CO2 emissions. According to the German Passive House Institute (PHI), founded by physicist Wolfgang Feist, who co-created the passive house concept, energy consumption can be reduced by up to 90 percent compared to average homes, up to 75 percent compared to newer buildings. While an existing home uses some 160 kilowatt-hours in heating energy per square meter of living space (kwH/m2) annually, residences built to the passive house standard use a maximum 15 kwH/m2.
Insulation is crucial to making these houses work. The walls in Disch’s complex, which comprises a 50-unit housing estate as well as a five-story commercial center (with Sattler’s penthouse on top), have “extra-thick insulating layers and are almost free of ‘thermal bridges,’” he says, referring to poorly insulated areas where heat gets lost. “The windows have infra-red-reflecting, vacuum-sealed triple glazing that allows lots of solar rays to enter but like the walls, prevents the resulting warmth from escaping again.” Each roof has an awning constructed at such an angle that it shields the interior from the high summer sun but lets the low winter sun permeate the dwelling. The panels on the roof generate electricity. All this, says Disch, “enables the structure to produce energy, use it intelligently, and retain it.” Five other German towns and cities are planning similar complexes.
Some worry that living in one of these novel houses might be too much like living in a thermos. Yes, your fuel bills are lower, but what if you felt like leaving the front door open on a summer evening? According to Sattler, that’s not a problem: “There is a popular prejudice that these houses have to be kept tightly shut so that no energy is lost, but that’s not true. You can open the windows like in any normal building. ”
Even with the doors and windows closed, the heat-exchange ventilation systems creates a pleasant, healthy indoor climate. Temperatures typically hover around 72 degrees Fahrenheit (22 degrees Celsius), whether it’s a December morning or a July afternoon. A 2005 report by the Austrian Ecology Institute found that the “more effective air exchange” in passive houses meant the concentration of pollutants “was markedly lower than in houses without ventilation systems where the same construction materials had been used.” The study also found that levels of dust, pollen, microbes and radon—an odorless, colorless gas associated with lung cancer—were all lower than in ordinary buildings.
All this energy-efficiency does, however, come at a price. A passive house can cost 10 to 15 percent more than a conventional home. Still, these costs are typically recouped over the lifetime of the building through reduced energy bills and lower maintenance expenditures. According to eco-house specialist Uwe Kettner, based in Saxony, Germany, a passive house with 1,500 square feet (140 square meters) of living space will save about $1,595 each year in winter fuel and hot water heating.
So far, some 15,000 passive homes have been built around the world, most of them in German-speaking countries and Scandinavia. “There’s only a handful of them in the U.S. at the moment,” says Bronwyn Barry of the Berkeley, California-based Quantum Builders, which is about to launch passive homes, called Q+, that produce more energy than they use. The number “will grow exponentially in the very near future,” Barry believes, in part because of proofs of concept like the Smith House in Urbana, Illinois.
Built in 2003, the Smith House is a two-bedroom, single-family residence with a finished floor area of 1,200 square feet (110 square meters) on two stories. The house “has a simple, compact shape that conserves energy,” says Katrin Klingenberg, the German-born architect who designed it, “because it results in the smallest possible surface-to-volume ratio. The smaller the ratio, the less heat is lost through the roof and walls.” Design principles like these mean passive houses can be built in places where fierce winters require reliable heating. The Waldsee BioHaus, built in 2006 in Bemidji in northern Minnesota, where winter temperatures can reach -2 degrees Fahrenheit (-19 degrees Celsius) keeps its heat thanks to extra-thick exterior walls made of insulated concrete blocks. Like the Smith House, the BioHaus is made from resources that are renewable, recycled or recyclable.
Existing homes can be retrofitted to become passive houses too, a potentially crucial component of any energy-efficient housing drive. Some 43 percent of U.S. carbon emissions comes from operating buildings, with homes constructed before 1939 consuming about 50 percent more energy per unit than those built in 2000. Architect Nabih Tahan practically rebuilt his 100-plus-year-old Berkeley, California, home, adding insulation and dual-paned windows and a heat- recovery ventilation system. Having lived in the revamped building for a year, Tahan is starting a consulting firm to assist in passive home design. He’s also hoping to start a pre-fabrication plant to manufacture wall, floor and roof panels.

With houses like Klingenberg’s and Tahan’s becoming more numerous and better known, “the critical mass has finally been reached and enough people in America are aware of the technology and its advantages,” Barry says. What’s needed now, she argues, are “financial incentives such as tax cuts or government subsidies” similar to the ones available in the European Union. “That would go a long way toward getting the show on the road.”
New construction “can come as a detached or semi-detached home, as a terraced house or interconnected row of houses,” Disch says. “It can be used for groups of houses or an entire housing estate like the one in Freiburg.” The buildings can also be built using local materials and in local architectural styles.
The biggest drawback is lack of sunlight. Homes in cloudy climes have more insulation and more efficient windows and heat-exchange systems to compensate. Larger buildings require larger solar arrays, so experts are creating a photovoltaic foil that can be applied to facades or windows, turning structures into solar power plants.
Sattler, for one, is happy with his energy-thrifty home. “An ordinary house or one like this?” he asks. “There is simply no contest.”
Ursula Sautter, who will be using her wood stove more often, wrote about hypnosis in the December 2008 issue.