Passivhaus is a type of design for homes that are super efficient. It was started in Germany in 1996 by physicist Dr. Wolfgang Feist. He developed the design based on superinsulated homes built in the United States and Canada during the 1970s. There are five basic elements in a Passivhaus design:
- High levels of insulation
- Reduce thermal bridges
- Airtightness
- “Energy gain” windows
- Heat recovery ventilation
Insulation is key to the Passivhaus’s efficiency. As the picture shows, walls are actually double framed. There is a wall inside the wall. This not only allows for double the insulation of a standard house, but cuts down on thermal bridges (places where heat/cold can move from exterior to interior without insulation) if the studs are offset. This technique does require more material for the double framing, but the energy saved will quickly offset the increased costs.
Sealing the gaps in a house is one of the easiest ways to reduce heat loss and save on energy. Most homes are so full of holes that the HVAC system is always fighting a losing battle. Designing a home for airtightness, and designing the system that will seal the exterior, is an important feature of the Passivhaus design. It requires much more than just a lot of caulking.
To meet the window requirements, manufacturers in Germany, Sweden, and Austria produce windows with foam sealed frames and argon-filled triple-glazed glass with two low-e coatings. That makes these windows some of the most efficient in the world. Studies have shown that the placement of the windows in a Passivhaus isn’t as critical as the other features. In this design, with such efficient windows, solar heat gain is not a concern.
The design guidelines highly recommend a heat recovery ventilator. This piece of equipment essentially “harvests” the residual heat in return air and uses it to warm the incoming outside air (the same process applies to cooling). Using this “waste heat,” the air is pre-warmed, and doesn’t require as much energy to heat. If the exterior sealing is done well, the house will require outside air ventilation. Most standard homes have enough leaks that this equipment isn’t necessary, but not so with a truly tight home.
Passivhaus is quickly becoming popular around the world. Known for its super efficiency, it is quickly gaining popularity with those who want to reduce their footprint.
For more information, see Passivhaus for Beginners.
Photo courtesy of Rob Harrison through a Creative Commons License.
