Energy independence and passive sustainability are always desirable features, but for Chalk Hill Cabin they were virtual necessities. “It’s in a remote part of the California Foothills, at almost 4,000 feet of elevation, so it sees some climatic extremes,” says David Arkin, AIA, LEED AP, of Arkin Tilt Architects in Berkeley, Calif. “It’s also several miles from the closest electrical connection, so the building envelope had to be very efficient and heat and cool itself passively as much as possible.” Its straw bale walls, finished with sprayed-earth stucco, contain substantial amounts of both insulation and thermal mass, Arkin notes. The resulting 12-hour thermal transfer cycle, he says, is “just about ideal.”
SIPs form the building’s shed roofs, which provide both mounting for photovoltaic panels and a deep overhang at the south-facing windows. Cement board siding at the cabin’s conventionally framed sections, cement board trim, and a standing seam metal roof yield a low-maintenance, highly fire-resistant shell. A ground-mounted solar thermal array provides domestic hot water. Surplus heat is shunted via heat-exchange pipes into a 3-foot-deep, insulated sand bed beneath the floor, which serves as a thermal flywheel for the living spaces.
The cabin’s interior consists of an open kitchen/living/dining room and, up a half flight, a small wing that holds a bathroom and mechanical equipment. A children’s sleeping loft tops the kitchen space, and a living area alcove closes with curtains to become the master bedroom. Floors are ground and polished concrete, while the interior stucco wears a plasterlike troweled finish. “There’s no sheetrock in the building,” Arkin says. Knotty pine covers the ceiling; the rest of the interior is finished in a variety of salvaged woods.
Tight and well insulated as it is, the cabin was not designed to meet Passive House standards, Arkin explains. The sand bed “acknowledges that over the course of the cold season, there’s going to be heat loss.” But the building replaces that lost heat—and supports its full electrical load—on its own. No building is completely an island, Arkin admits, “but all our energy comes from the sun, so we’re going to take that.”