Passive house saves energy aggressively

Cranking up the heater or throwing on an extra sweater are two ways to cope with a drafty house that allows chilly air to seep in through cracks, doors and windows.

When the sun blazes in the summer, that same house warms up rapidly, prompting people who live there to close the shades or drapes, pour an icy beverage and possibly flip on an air-circulating fan.

A new concept in energy efficiency, known as the “passive house,” sets specific standards for designing a home that reduces — or completely eliminates — the need for a furnace or air conditioner. The home is constructed to be super energy-efficient and to regulate air temperature in a “passive” manner.

An airtight structure adhering to passive house guidelines could reduce year-round energy costs by an estimated 80 percent.

It’s been described as working like a sealed envelope or thermos bottle, preserving hot and cold equally effectively. Heat generated by appliances, bathing and the body itself are factored into calculations.

Accordingly, a house that’s vacant most of the day would generate less heat than one where occupants are using computers, TVs and kitchen and laundry appliances.

More than 10,000 passive houses have been built in Europe since the design approach was introduced in Germany in the early 1990s. But only a handful have been constructed in the United States.

Early advocate

Petaluma-based architect Bill Wolpert, principal of Green Building Architects, has been interested in creating energy-efficient structures since he was a student at Cal Poly San Luis Obispo in the 1970s.

Early in Wolpert’s career, when gas, electricity and water costs were low, energy efficiency wasn’t a top priority. But now, most clients want buildings that make abundant use of solar energy, have well-insulated walls, doors and windows, conserve water and are constructed with recycled and/or nontoxic materials.

Last year, Wolpert attended a lecture by Berkeley architect Nabih Tahan, a passive house pioneer in California, and afterward asked two of his residential clients in Sonoma County if they wanted to incorporate passive house standards into their project, even though the design was nearing completion.

The first certified passive house in the United States was built in Urbana, Ill., in 2003 by German architect Katrin Klingenberg, who established the Passive House Institute US. In January 2008, it was established as the official certifying body in North America by the the Passivhaus Institut in Darmstadt, Germany.

Passive house building techniques include use of the latest construction materials, such as multipane windows containing a thin metallic film, argon gas and a layer of mylar film, to create an insulating “sandwich.”

A special feature is a central ventilation system with warm air moving through it alongside cold air coming in from the outside. This heat exchange is considered to be 90¬percent efficient. An “energy recovery ventilator” provides a constant supply of fresh, filtered air and creates good interior air quality while maintaining a comfortable temperature.

Previous efforts to create airtight construction have resulted in problems with mildew and mold, Wolpert said.

Another key design consideration is positioning a house to take advantage of maximum sun exposure.

Scrapping the dome

Wolpert’s clients, Chris Read and Chris Vein, are San Francisco residents who spend weekends on a seven-acre, oak-studded property with stunning views above Sonoma.

They knew when they purchased their 30-year-old geodesic dome residence three years ago it would need remodeling, but as they began investigating improvements, the men realized it would be easier to scrap the dome and design a modern home that could be smaller, energy-efficient and take full advantage of the site.

“Our goal was not to be a super-green client. But we’d like to do as much as we can to reduce energy consumption," Chris Read said. “We’re into balancing the practical with the (passive house) standard itself.”

They agreed with Wolpert’s suggestion to hire energy consultant Graham Irwin of Remodel Guidance in Fairfax to do a detailed energy analysis using computer software from the Passive House Institute US. Irwin, who is certified by the institute, found some design elements were fine, but others could be improved, such as changing window locations to allow more air flow and choosing ultra-thick insulation for the walls.

Wolpert also used software showing where the sun and its shadow would fall on the house from dawn to dusk, resulting in useful information about positioning windows.

While Wolpert and his clients haven’t finalized the plans and building materials, they acknowledge it will be a home in the passive house spirit even if it might not meet the exact energy usage criteria for certification.

“We’re getting something that makes us feel better about the energy we do have to burn,” Read said, noting that the house will have a floor radiant heating system and will use materials from the deconstructed dome and salvage yards.

Typical home leaky

Many communities have voluntary standards for green building, but lack specific thresholds for carbon output and energy performance. Following passage in 2006 of Assembly Bill 32, the California Global Warming Solutions Act, municipalities are looking at numerous ways to reduce greenhouse gas emissions, including guidelines for energy consumption in remodels and new home construction.

“A typical home in California leaks 30 percent of air to the outside. It has to do with standard of work. A lot of problems in existing homes are the fault of the craftsmanship,” Wolpert said.

If Read and Vein agree to the recommended window and insulation changes to boost energy efficiency, he believes the radiant floor heating they’re planning could make the house too hot. He hasn’t suggested, however, that they construct it with no heat source.

“The passive house idea wasn’t on my radar until two years ago. This way of doing things is a little different,” Wolpert said. “It if works in Germany, there’s no reason it wouldn’t work here. We have the ideal climate.”