Outside, voices harmonizing to a Mexican radio station float on the evening air past walls and wedge-shaped pillars that rise out of the ground like Stonehenge monoliths. Inside, a house is under construction. Scaffolds lean, work lights shine, and craftsmen sing and stucco with care.

“There’s joy in these walls,” says architect David Barrett of the house that he and his wife and fellow architect, Betzi Bliklen Barrett, designed and built for themselves and their son, Will, in Boulder, Colorado.

Known as the “garden house” because it is at the northeast boundary of a local community garden site, the Barretts’ 2,500-square-foot home and detached garage with a 575-square-foot studio are made of stuccoed Cempo, corrugated cementitious panels (CCP) from Denmark, and Hardiplank fiber-cement exterior siding. Cempo, an energy efficient building system made of Portland cement and recycled polystyrene (the white packing material for electronic equipment), consists of 86 percent recycled material. The forms contain a series of channels—spaced on sixteen-inch centers—that run vertically and horizontally and are filled with structural concrete and rebar, which creates a post and beam matrix that replaces conventional framing.

“The idea of building with something that would have gone into a landfill is great,” David says of Cempo. “It’s a highly insulative, thicker wall, and the cementitious surface is alive, rather than plasticized, which seemed to be the right idea for being in the city.” And while the Barretts considered building with straw bale, Betzi says straw bale walls would have been too thick for their 70-by-140-foot lot, where every inch of space is important.

Construction on the Barretts’ home took fifteen months, and the cost came to around $200 a square foot. “It’s not always cheap to build with alternative materials,” Betzi says. “But I don’t want to put people off because it can be done less expensively, and we continue to learn how. Large expanses of Cempo are a much cheaper way to use the material, but we chose to cut, mold, and form it.”

City order and natural order

Although much of their architectural design work is a more organic approach to mountainous, rural settings, the Barretts thoroughly enjoyed working with a city site. “Everything’s always related to nature, but there’s another kind of discipline in a city,” David says. “This house has a city order and then a natural order.”