Cobbled Together

As builders and homeowners cast about for building materials more sustainable than wood, some are looking backward, to practices used in places where wood (or a tool with which to cut it) was hard to come by.

That's what led Linda Smiley and Ianto Evans to build with "cob," an adobe-like cement made from clay-rich soil, sand, water and straw. Smiley, at the time a recreational therapist, and Evans, an inventor and teacher, wanted to expand their 100-year-old wooden cabin in Cottage Grove, Oregon, but out of respect for Oregon's heavily logged forests, they wanted to do it using as few trees as possible—leaving them with limited options in the rainy northwest. The conditions reminded Evans' of his native Wales, where traditional cob cottages have survived for centuries in the notorious damp. Smiley and Evans built their 120-square-foot addition using cob and, struck by its simplicity and solidity, began hosting workshops and traveling to builders' conferences to share what they'd learned. Eventually they founded the Cob Cottage Company, where they offer "how-to" classes on working with cob. They also co-authored The Hand-Sculpted House: A Practical and Philosophical Guide to Building a Cob Cottage (Chelsea Green, 2002, $35).

Cob has notable advantages: insects don’t eat it, so you’re less likely to need pesticides, and it doesn’t burn. Because cob homes “breathe,” absorbing and releasing air and moisture, they offer better indoor air quality than conventional homes. British Columbia-based residential designer Elke Cole turned to cob to address her clients’ chemical sensitivities, which are triggered by the carcinogenic formaldehyde and other volatile organic compounds that conventional paints, glues and finishes emit.

Cob’s breathing also makes for “beautiful” climate control, says Cole. “Cob isn’t great for insulation,” she explains, “but it has thermal mass,” which essentially means it’s good at holding a constant temperature (read: lower heating and cooling bills). It slowly warms during sunny periods and then slowly releases that warmth when it’s cool or overcast. Cole and other cob-dwellers also draw comfort from the fact that cob homes won’t harm their surroundings. Because it’s made entirely from local, natural materials, the cob elements of home construction produce “zero garbage,” Cole says.

Building with cob requires mixing its ingredients into a sticky mass and then piling still-wet lumps or "loaves" of cob on top of each other to form walls. But walls are not all you can build with it. Tucson-based cob builder Joelee Joyce uses cob for all kinds of projects including garden benches and outdoor cob ovens. Sasha Rabin, co-founder of Seven Generations Natural Builders in Arizona, has used cob for bookcases, even sculptures.