A recent article in the New York Times highlighted a topic I’d been hearing a lot about lately: “passive house.” Passive house is a methodology that takes advantage of materials and design 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.
The passive house concept is emerging as an important strategy to reduce emissions and energy use in the building sector.
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I should say first of all that almost everything I know about passive house comes to me from two local architects who are newly certified in passive house design. Rob Harrison is actually right in the Vance Building where Sightline’s offices are located and Jim Burton has been leading a number of efforts for the Northwest Eco Building Guild (I’ve written about the Guild before). I know they’ll add, correct, and expand my points in the comments section. One of the first things that both Harrison and Burton make clear to me is that passive house is a somewhat misleading term because it doesn’t just apply to houses but to all types of buildings. And passive house is a methodology not an adjective. It might have been better left in its German form, Passivhaus.
- 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 people in the building.
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. 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. 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.
Intrigued? So am I. Passivhaus can be more expensive because of the materials and the design. But advocates argue that the extra cost is far exceeded by the energy savings. That’s important. We still have to figure out how to pay for the up front work which can be expensive, but while we are figuring out how to finance the efficiencies that are good for the planet, our economy, and the health and wellness of people, I am glad to add Passivhaus to my list of things to learn more about.