Saturday, March 7, 2009


A few days ago in Alingsås we visited a school where technology and technical education around the Passivhus concept are taught. Passivhus is a type of extremely energy-efficient housing that is now being used in some places in Sweden. Alingsås has a few Passivhus’s, including a day care center in Stadskogen.

According to our tour, the first Passivhus was completed in 2002. The basic idea is to insulate and seal the building extremely well and use a heat recovery exchange system (recycling filtered warm air from bathrooms and kitchens back into the house), body heat, and heat from appliances as the heat sources. We were told that a secondary heating system can be installed if desired (if the house is left for a few weeks with no appliances or body heat, it can take a while to warm up again). Triple pane glass windows, typically wood frame with a break in the thermal bridge, are used. There is a special system used to apply the vapor barrier around windows and for homes with more than one level. Insulation is high-pressure blown-in cellulose (recycled newspaper). A blower door test is required prior to rigid insulation (after blown-in) to ensure the envelope is sealed properly. The Swedes measure envelope insulation in U-values (roughly the inverse of R-values) and I haven’t had a chance to convert them yet. The insulation is typically at least as follows, in U-value:
Walls: 0.10 – 40cm
Attic: 0.08 – 50cm
Foundation: 0.088 – 30cm
Windows: 0.80

Right now Passivhus construction is typically stick-built on site, but they are looking into ways of building prefabricated Passivhus homes (which are much more common in Sweden – 90% of Swedish homes are prefab). We were told that the cost of a Passivhus is 5% over normal, but I don’t know if that means normal for stick-built or normal for prefab. Sweden is having the same challenge of making existing housing more sustainable and energy-efficient, and Passivhus is also working on renovation projects. One project in Alingsås, Brogotten, is a multi-family Passivhus remodel success story – average energy use went from 216 kWh to 92 kWh in one study.
One thing I really brought away from this visit was that making energy-efficient buildings only gives the possibility of lower bills and an energy-efficient lifestyle – behavior is a very important determining factor to a projects success. We need to be sure to include homeowner/resident education about consumption practices as part of green building, as well as building the houses themselves. This is common sense of course, but realizing that Sweden has the same challenge really hit the message home.

Another interesting part of the visit was actually about Germany. In some areas of Germany, where if a project removes green space, that exact amount of green space must be put back into the project. Passivhus’s in Germany will often take the exact sod/grass from the site and put it right on the roof, which adds insulation in the winter and keeps the house cool in the summer. Apparently the weight of the added roof elements is not an issue for engineering because they have high snow load requirements just as Minnesota does.

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