In September 2009 I completed a deep energy retrofit ("A Cost-Effective Energy Retrofit," 8/10) on a small house in Point Reyes Station, Calif., some 50 miles north of San Francisco. The owners were so pleased with the results they asked if I would build a new 750-square-foot rental unit in the back of their property, designed to meet the demanding Passive House energy-use standard. (Because affordable rental housing in California is in such short supply, the state encourages the construction of such second units - though they're limited to a maximum footprint of 750 square feet.)

I began work in February 2010, using a set of plans developed by architect James Bill. It was to be the first new PH project in California. There were no textbooks, elders, or old-timers to fall back on for advice or tips. My subs had no idea what they were getting into. My workers had worked on the retrofit and had the basic concepts of...

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