A bench built by the Mudgirls at the Nanaimo Community Gardens on Vancouver Island. (Mudgirls Natural Building Collective)
Used to build homes and baking ovens for centuries, cob is a mixture of clay, sand, straw, water, and earth, similar to adobe. It is fireproof, earthquake resistant, long-lasting, and relatively inexpensive.
Cob buildings can be found in many parts of the world including on the west coast of both Canada and the United States. In Devon, England, 500-year-old whitewashed cob cottages with thatched roofs are still being lived in today, having easily withstood the passage of time.
Mixed by hand—and often by foot—cob is a creative, sculptable material that is breathable and healthy, says Rose Dickson of Mudgirls Natural Building Collective, a for-hire network of women based on Vancouver Island and the Gulf Islands who build cob houses.
“Cob is non toxic,” Dickson says. “As far as green materials go, it has low-embodied energy, which is a term we apply to things that don’t take very much processing.”
Cob also avoids the outgassing from glues and chemicals that occurs with conventional building materials.
“As long as it’s finished properly so it’s not going to be dusty, it’s a completely healthy environment,” she says.
And because it absorbs the temperature, cob is also “excellent for passive solar heating” as it has thermal mass—it retains heat in winter and remains cool in summer.
The Mudgirls specialize in the traditional cob-building method, meaning cement foundations are out. Where possible, only natural, local materials are used. They do nearly everything “from scratch,” and disturbance to the surrounding environment is kept to a minimum.
The women use the dry-stack technique in which “rocks are carefully and consciously stacked together so that they fit securely.” Cob is then applied by hand directly on top of the rocks. The posts and beams come from recycled wood, and cedar shakes rather than shingles compose the roof. A living roof will be made of moss, grass, or herbs.
A particular style used by the collective is the rounded form which creates a stronger building that can be moulded in imaginative ways.
Mudgirls build the cob walls for a home on Salt Spring Island. (Mudgirls Natural Building Collective)
Since conventional-sized cob houses cannot be built to follow the building code in most areas of British Columbia, the Mudgirls build mostly small guest cabins and sheds measuring around 100 square feet. At this size, no permit is required.
While the materials are cheap or often even free, building a cob house is a labour-intensive process and that drives up the cost. However, there’s a lot of work that doesn’t need any particular expertise which people can do themselves, says Dickson.
If a cob house has a good foundation and is properly looked after, it will never rot or decay. On the other hand, if neglected or demolished, it will decompose naturally without damaging the environment, Dickson says.
“If for any reason it is abandoned and the weather started to get at it, it would return to the earth and you could plant an organic garden on top of it years later.”
While specializing in building with cob, the collective also uses other natural materials such as strawbale, driftwood, adobe, cordwood, and recycled materials like glass, car tires, and glass bottles.
