Calif. retrofit shoots for Passive House status

The home's air-tight sheathing will be covered by four inches of foam.

A home builder in California’s Napa Valley is working on what he says will be the first retrofit in the state to be certified as a Passive House. When the work on the 1,800-square-foot home, which was built in 1960, is complete, it’s mechanical systems will use 90 percent less energy than a home built to code, says Rick Milburn, president and CEO of Solar Knights Construction, Inc.

Although the project is just 60 percent complete, Milburn says he is comfortable making claims about its future performance because the project team used the Passive House Planning Package (PHPP) to model energy use. PHPP is a software package designed by one of the creators of the original German Passivhaus Standard. It has been proven to be very accurate in predicting building energy use over a large sample, according to the PassivHaus Institute. “It goes way beyond the software we use for meeting Title 24 requirements,” Milburn says.

In the Napa Valley home retrofit, Milburn’s 20-year-old company was able to retain 40 percent of the original walls. The design calls for 16-foot-high sliding triple-pane glass doors and triple-pane windows made in Germany. A “super insulated airtight shell” that includes four inches of foam between the interior walls—which are wrapped in an airtight barrier—and the siding, is planned as well.

Passive House measures will add about 10 percent to 15 percent to project costs, but lower utility bills will bring payback in about nine years, Milburn says. However, “It doesn’t have to be about high-end homes here,” he says. In Germany, building to the standard supports medium-sized manufacturing efforts there. The United States could do the same, but its builders and green building certifications need to focus on energy efficiency and not an array of points if that is to happen.

“I’ve worked on LEED projects and Build it Green Projects,” Milburn says. “They’re all lacking a focus. With Passive House, you can make a huge difference."