Last night BuildItGreen's South Bay Professional Guild hosted Nabih Tahan, a Berkeley-based architect who was recently featured in a New York Times article on passive houses. Nabih discussed the passive house concept and how it is being applied in Germany and the rest of Europe, as well as his experience building Low Energy Houses (Niedrigenergiehaus - the generation of homes before the passive houses) in Austria and remodeling his conventional house in the Berkeley flatlands into a passive house.
The term "passive house" reflects the concept that these houses do not have heaters to provide warmth. Instead, they "passively" recover heat from all the other activities in the home - such as cooking, lighting, and even human activity. To enable this, a passive house is highly insulated, with an airtight building envelope, so that no heat can escape. To keep the air quality high, passive houses use "heat recovery ventilators" or "energy recovery ventilators" with air-to-air heat exchangers to constantly replace the old inside air with new outside air, while keeping the heat from the old air inside.
Passive houses typically use about 80% less energy for heating and cooling than conventionally-built houses.
Tahan's talk covered a huge amount of ground. Some of the high points included:
A description, with a number of photos and a video, of the current German and Austrian technologies for building houses and multi-family residences. These homes are built in factories, by automated, computer-controlled machines, and assembled in a few days on site. Because all the pieces are designed to high tolerances, the building sites are very quiet - if you hear a power saw on one of these sites, you know someone made a mistake.
He showed a picture of "model home mall" in Austria (here's something similar in Germany - in German), where more than 40 of these pre-built home builders have built 80 model homes that you can tour. The homes range in size and style from modest single family houses to large mini-mansions, to apartment buildings.
I asked what one change in the U.S. would make it easier to build passive houses here. He said better windows and doors. Insulated and well-sealed windows and doors, often with triple-glazing and special coatings on the glass, comprise a key component of passive houses in terms of keeping the building envelope airtight. There are many manufacturers of these components in Germany and the rest of Europe, but none to very few in the States. In fact, Tahan is currently in discussions with investors on starting a factory to build these components, in partnership with an Austrian company.
For his Berkeley house, he decided to work with a U.S. supplier, Sierra Pacific, to demonstrate that the passive house standard is possible in the California climate with local products. In any case, buying the windows in Austria would have cost less than buying them here, but the cost of shipping would have made the Austrian windows more expensive.
In building a passive house, airtightness is as important as the insulation - they work hand in hand. And it's the most difficult part, especially in the United States where buildings are not constructed by computer-controlled machines.
In Europe, building a passive house costs 4-5% more than conventional construction, but it saves 80% of the energy. Currently it's a somewhat bigger premium to build a passive house in the States, due to lack of suppliers and know-how.
The passive house concept and approach is clearly a component of a zero-net energy home program. Reducing the amount of energy a home uses means it's a lot easier and cheaper to generate that energy onsite. Architects like Tahan will be a key enabler of getting to the 2018 goal of 100% zero net energy homes in California.
This was an excellent talk, and I'm looking forward to hearing more from Nabih Tahan, and attending more BuildItGreen functions. If they're all at this level, they'll be a great resource for getting California to the goal of 100% zero net energy new houses by 2018.
Update (2/13/09): Nabih tells me that the Passive House California Group has just set up their website, where you can read about their next group meeting and other topics.