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Passive House: Super energy efficient housing

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

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.

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