October 27, 2010
Washington’s first passive house nears completion. Photo: Rob Harrison
You might have been hearing lately about “passive houses,” a term that conjures up the question “how could an inanimate object like a house be other than passive.” After all, a house just sits there doesn’t it?
These houses actually are built to do a lot of work; keeping the inside warm or cool, and keeping the elements at bay. Some of them only require the equivalent of a hair dryer for heating, even in cold Northwest climates.
Part of the problem is the term. In this article I’m going to leave the term un-translated from the German “Passivhaus”, even thought it applies to all buildings, not just single family residential homes. It is really a methodology gaining ground in the architectural community to dramatically limit energy use.
The Northwest has an abundance of experts on Passivehause concepts; people like architects, Rob Harrison and Jim Burton. Burton has been leading a number of efforts for the Northwest EcoBuilding Guild (I’ve written about the Guild’s work on creating flexible single family housing), including Passivhaus. Harrison is working on Passivehous designs from his offices in Seattle.
How does Passivhaus work? Here’s a rundown based on Burton’s description of the Passivhaus Standard. Passivhaus buildings have:
- A super-insulated envelope (in our climate, perhaps an R-48 wall, R60 roof);
- High-performance triple-glazed windows (U-value .15 or lower);
- Reduction or elimination of thermal bridging;
- Super airtight construction (has to meet Air Change Rate of .6 ACH @ 50 Pascals, almost unheard of, and probably the hardest part of building a passive house);
- Heat-recovery ventilation; and
- Use of passive sources for heat gain – solar of course, but also lighting, appliances and even people in the building.
Passivhaus design takes advantage of materials to dramatically limit total energy consumption by reducing the need for heating and cooling. It’s ‘passive’ because keeping a building warm or cool doesn’t require flipping a switch or adjusting a thermostat. In other words, it’s self regulating. The building—because of materials and design—retains heat when it’s needed most without the need to heat up cold air and move it around.
Getting Passivhaus right is complicated and requires expertise, which is why there is a certification program. But once Passivhaus is implemented in design and construction, the savings are demonstrable. Some of that is pretty technical stuff. But a Passivhaus building would essentially be off the grid, using natural sources of heat to keep the building warm, including the body heat of people in the building and sunlight, for example.
According to Burton,
The super-efficient envelope reduces the heating load so much that the building does not need a conventional heating system. In practice that heating is often provided by a small coil
—electric or hydronic
—in the code-required ventilation system. The Passive House Institute (PHIUS) likes to say that the heating system in a PH is limited to 2000 watts, the size of a hair dryer.
One home, called the Shift House, is in Hood River, Ore. The Shift House will use about 15 kilowatt-hours per square meter compared to the average American home which uses almost ten times the energy, about 130 kilowatt-hours per square meter.
The energy savings are significant which is good for stemming the problems of climate change. What about affordability? Is Passivhaus an expensive novelty? Not really. According to PHIUS “to achieve passive house standard requires an additional upfront investment of approximately 10 percent of the construction budget, as compared to regular energy code-compliant 2×4 construction.” Considering the reduced operating costs, Passivhaus might be a good long term investment, especially for multifamily or commercial buildings.
But here’s the aggressive part. Federal, state and local governments looking for opportunities to incentivize energy efficiency should consider Passivhaus along with district energy, and easier financing for commercial and residential efficiency. As more Passivhaus buildings go into construction architects and builders should be able to find ways to reduce up front costs and if energy prices go up in the future the payoff will become more immediate. Tax credits and grants for Passivhaus pilots would be a small and worthwhile investment in improving the methodology and planning to reduce energy consumption in the future.
As we enter an era of increased concerns around energy efficiency and climate change, I expect to see an aggressive expansion of Passivhaus techniques in future buildings.
For a great discussion on the ins and outs of Passivhaus check out this post I wrote a couple of weeks ago.