When Katrin Klingenberg designed the first single-family Passivhaus in the U.S. in 2003, she used 12-inch-deep I-joists (TJIs) as wall studs. Located in Urbana, Illinois, the house was sheathed on the exterior side of the vertical I-joists with vapor-permeable fiberboard and on the interior with OSB, which acted as an interior air barrier, an interior vapor retarder, and structural bracing. The bays of the engineered studs were filled with blown-in fiberglass insulation.
In 2007, Klingenberg explained the principles behind her preferred wall design: “OSB has a vapor permeability of about 0.8 (considered to be semi-impermeable; that’s why we use it as vapor retarder on the inside of our frame work). … The rule of thumb for designing a diffusion-open wall assembly in heating climates is, that the outside sheathing should have a minimum of five times the permeability of the inside vapor retarder … So, with the use of the bituminous-coated structural fiberboard on the outside of our wall assemblies we are just in range.”
Klingenberg used the same wall system on several subsequent projects, including two single-family homes on Fairview Avenue in Urbana, Illinois.
In 2004, I interviewed Tom Huettner, one of the carpenters who (along with Ed Sindelar) built the first Klingenberg-designed Passivhaus in 2003. Huettner explained that the wall system was “based on a German design.” Klingenberg told me that she consulted a German document (“Balloon und Platform Framing Details”) published by Weyerhauser. Because aspects of this wall assembly have roots in Germany, many American builders assume that the system is common in Europe. In fact, few European builders use the system.
After completing her house, Klingenberg went on to found the Passive House Institute U.S. Klingenberg is a frequent public speaker on the topic of Passivhaus construction techniques, so her wall details have been copied by cold-climate builders all over the…