Thick straw bales in the walls of this off-grid home help moderate interior temperatures. The home’s south-facing windows admit the sun’s heat energy, reducing the need for mechanical heating.
Marilyn Pedretti’s house was inspired by the two years she spent in El Paso, Texas, helping build straw bale homes for an affordable housing community called Tierra Madre. While these structures were embraced in the south, says Marilyn, “people [here] thought I was crazy.” Not only were straw bale structures practically unheard of in her small community of Holmen, Wisconsin, but Pedretti planned to act as general contractor for the project while maintaining her other jobs.
She attended the Midwest Renewable Energy Association’s annual energy fair for ideas and built a garage to gain some skills. She also started collecting materials, including windows and doors, and hired architect Todd Osman to help with the design. With the help of friends and family, and theme parties like “Get Plastered with Marilyn,” Pedretti completed her house in a year and a half.
The home’s thick, insulated walls and passive solar design help moderate indoor temperatures, even during Wisconsin’s chilly winters and humid summers. Few, narrow windows on the north side minimize heat loss, while multiple windows on the south face admit solar gain, warming the space in winter. Adequate overhangs on the south shade these same windows from the hot summer sun. To the west, an eight-foot-deep porch keeps the sun out on late summer afternoons.
For backup heating, the four-inch concrete slab contains hydronic tubing. Pedretti sets the temperature of the concrete at 72°F to 74°F, resulting in ambient temperatures between 58°F and 65°F. The hydronic system relies on a propane-fueled instantaneous water heater.
A pole-mounted 1 kW PV array and battery bank provide the home with electricity and power the pump for her well. Pedretti relies on a portable generator “six to 10 times a year” for backup; she goes through a single 300-gallon propane tank annually. “November and December can be pretty challenging; sometimes we get three to four days in a row without sun,” she says. She considered a grid-tied system but didn’t relish the notion of spending $4,000 just to bring electricity to the house, not to mention a basic monthly fee of nearly $30 just for the privilege of selling electricity back to the grid.
Since its completion in 2007, Pedretti’s house has been featured on the MREA’s Wisconsin Solar Tour four out of six years. She regularly opens up her house to groups from schools and colleges, and other community groups. Though her home may not have earned any official certifications, Pedretti enjoys what she calls a “happy living award.” Nobody calls her crazy anymore, either.