The first single-family Passivhaus in the U.S. was completed by Katrin Klingenberg in 2004. Klingenberg’s superinsulated home in Urbana, Illinois includes two unusual features: a ventilation system that pulls fresh outdoor air through a buried earth tube, and walls that include an interior layer of OSB. These details were not invented by Klingenberg; she adopted practices that were commonly used by European Passivhaus builders.
Although many North American designers have copied Klingenberg’s details, earth tubes are beginning to fall out of favor. Yet even in 2012, earth tubes are still being promoted by some Passivhaus builders.
By December 2007, when I first interviewed Dr. Wolfgang Feist, the director of the Passivhaus Institut, Feist was no longer recommending earth tubes. When I asked Feist whether earth tubes in Europe had experienced problems with condensation and mold, he answered, “There were problems in northern Europe, especially in Scandinavia. In Central Europe we haven’t had any hygienic problems so far. Actually, I’m not sure why we don’t have these problems in Central Europe. But I don’t advertise these systems any more, mainly because they are too expensive.”
The classic European wall
European Passivhaus builders (and Klingenberg) favor the use of a superinsulated wall system with three distinguishing characteristics:
- Vapor-permeable exterior sheathing made of fiberboard.
- Thick insulation — usually cellulose or blown-in fiberglass rather than spray foam or rigid foam.
- A layer of OSB on the interior side of the wall to act as an air barrier and vapor retarder.
Many American Passivhaus proponents (including Albert Rooks of Small Planet Workshop) endorse this type of wall assembly. They often claim that such a wall assembly is a better choice than one with thick exterior foam, arguing that it’s best to use vapor-permeable exterior sheathing so that a wall can dry to…