The first time I saw people building with cob I remembered making mud pies, that quintessential summer activity of every childhood lived where there is dirt. Cob, from an old English word meaning lump, is the oldest technology for building with earth, utilizing gooey straw-laced mud clumped handful by handful into thick walls. Since they are all of one piece, cob buildings are strong, and their mass makes an interior that stays cool in summer and holds heat in winter. There are cob houses built in Britain in the 1500s that are not only still occupied but in greater demand than ever. More recently, rounded sculptural cob houses have begun to appear like mushrooms after rain in the back woods of Oregon and Northern California, built by their owners without permits or prior experience.
But then, cob building is so simple, any three-year-old can participate. The materials–earth, sand, straw, water–are not only cheap and near at hand but nontoxic and renewable, making cob the most eco-friendly extreme in building technologies. The hitch? It’s as slow as you might imagine building a house out of mud pies could be. Even a structure small enough that a building permit is not required–120 square feet or less –could use the labor of not only the whole family but the entire neighborhood.
The cob itself imposes a height limit of eight inches per day–any higher and it starts to “splooge”–a cobber’s term that describes how the wet mud slumps from its own weight. But look on the bright side–cob building could be the perfect antidote to a rushed work life. Building a cob potting shed, say, could be a backyard summer project that provides hard physical exercise, a full social life, and a meditation practice all rolled into one, with the added bonus of gaining a permanent garden structure. Don’t need a potting shed? Then try a curved bench that fans out from your house or a covered sitting nook–organic designs are a cinch with cob.Back in 1997, Northside community gardener Jim Cisney thought about building a cob toolshed at the garden’s BARTside plot, a block north of Hopkins Street on Northside Street. At the Peralta Community Garden on the next block, architect John Fordice was designing a wooden toolshed but looking for an occasion to try cob. Environmentalist Karl Linn, whose work had helped shape both gardens, connected the two up. By August 1998, construction begun on Northside Community Garden’s cob toolshed, with John Fordice in charge and Linn providing midwifery services in the background. The project was supposed to take three months to complete, but here’s where cob can really mess with your expectations–it took two and a half years. The cob “tool temple,” as the structure has come to be called, was formally dedicated at a ceremony attended by over a hundred neighbors on June 3. Visitors strolled past burning sage sticks on the welcoming “arms” that make a seating area at the little building’s entrance, into the cool, roundly triangular interior, still so sparsely furnished with garden implements that it really does seem more temple than toolshed. Recycled beams fan overhead, and the cavelike embrace of earth is lightened by a diamond-shaped skylight and two windows, also recycled. The earth roof was in full bloom with the pink shades of native clarkias, while California poppies peeked through, next in line to bloom. The effect is both whimsical and massive, an artful folly built to last for centuries.
Examining the toolshed’s construction explains both why it took so long to build and why it’s likely to last so long. First, an eight-inch-deep reinforced concrete foundation was laid for the building; then a one-and-a-half-foot base wall was built up of broken sidewalk–called “urbanite” by the eco-builders–to keep the water-soluble cob up away from the ground. There are not yet any accepted standards for building with cob–though the technique is ancient, it has not re-entered our construction vocabulary –so every builder is on his or her own. Karl Linn insisted that Fordice overengineer the toolshed, since it was to be a visible educational edifice on public property. For seismic stabilization, Fordice adapted techniques the Getty Conservation Institute had developed for use on historic adobe buildings. He attached one-quarter-inch diameter wires every two feet around the perimeter. The wires ran vertically from the concrete foundation, through the urbanite layer, all the way up the walls embedded in the cob, and tied into the reinforced concrete bond beam ringing the top. This treatment is very likely much more than is necessary–but we don’t yet know what is necessary with cob. Traditionally, the earth used for cob buildings comes from the site–you can create a backyard cob teahouse and a frog pond at the same time. Northside Community Garden had no room for a pond, so a total of fifty cubic yards of soil was trucked in, mainly from the R.C. Knapp Co.’s Seabreeze Soil Depot at the base of University Avenue. Since the soil comes from building site excavations, it had to be sifted at the garden to rid it of rocks, big chunks of clay, nails, glass, and oddities. Sifting reduced the volume of usable soil by a third, and the tailings were returned to the depot for a less exacting use. The next step was to create just the right mix of soil, sand, straw, and water. Fordice made test lumps, carefully measuring proportions as he added sand to the mud until the lump fell apart, then backing off on the sand just enough that the lump would hold. The amounts had to be retested with every batch of soil. West Berkeley topsoil doesn’t need much sand, but soil from several feet below the surface, or from the hills, contains much more clay, and without added sand would shrink and crack as it dried. Straw is added to further control cracking and add tensile strength to the glop. The proper consistency is an easy thing to learn by experience and impossible by the book.
On weekends, Fordice and garden volunteers used a small cement mixer to make batches of soil, sand, and water. They dumped the mix onto a tarp and worked the straw in with their feet (straw would clog the mixer). Then they built up the walls, mashing the new layer into the old with a wooden tool invented by Fordice and called a “cobber’s thumb.” Fordice used a height-to-thickness ratio of seven to one for the shed–one-foot-thick walls that are seven feet high–but he recommends even thicker walls, ideally four to one, especially for structures not seismically reinforced as this one was. To keep the cob from drying out too quickly, Fordice put wet burlap on top of the walls and then wrapped them in tarps between cobbing sessions.
At every stage of the construction, materials were salvaged, found, and donated. The hauling of soil, sand, cement, and lumber were likewise volunteered. After a year of weekends, even the enthusiasm of the stalwart Northside gardeners understandably waned, and fresh volunteers needed to be recruited from the wider community. A similar project in your backyard might move along considerably more smoothly.
Once the walls were up, forms had to be built to pour the concrete bond beam around the top–an extra, and perhaps redundant, measure of earthquake safety. Recycled roof beams and tongue and groove roof decking then formed the base for the wide-eaved living roof. A carpet pad, found curbside on trash hauling day, tops the roof deck, cushioning a layer of sheet rubber. Six inches of lightweight soil mix went on top, planted in native flowers and grasses.
John Fordice’s tips for backyard cobbers start with the English saying, “Give a cob house a good pair of boots and a hat and it will last forever.” In other words, a sound foundation to keep the cob away from wet ground, and a roof with wide eaves to deflect rain from the walls. “Start small,” he advises, “and enlist your friends.” Two books about cob building are available: The Cobber’s Companion by Michael G. Smith and The Cob Builder’s Handbook by Becky Bee both provide a good introduction and overview of the subject.
But there’s nothing like hands-on training, and luckily, you can volunteer this summer at Fordice’s current project, a small cob greenhouse at Malcolm X School in Berkeley. Work will proceed through the summer school session, with students and other community members participating. After that, Fordice envisions a more ambitious project involving a gathering circle with cob seating and a timber-framed roof at the Richmond Community Garden. For information about volunteering for either project, contact Fordice via e-mail at otherfish@ home.com.For now, cob strikes many people as a weird novelty, practical for a doghouse-size project but not for a real home. Cob enthusiasts see a much bigger picture in which an earth-based building technology saves our forests, brings us back to a reverence for the earth, and provides us with structures that last many hundreds of years. The environmental savings could be substantial–think not only of trees left standing but of all the manufactured materials in standard construction, and the transportation costs. The critical next step, at least according to John Fordice, is to get cob into the building code.County building codes specify standards for various construction methods and materials in order to insure the safety and performance of structures. Standards are based on laboratory tests of tensile and compressive strength, load-bearing capacity, fire-resistance–data Fordice estimates could be comprehensively gathered over a two-year period with a half-million-dollar budget. In the meantime, cob building projects can be considered under the “alternate materials and methods section” of the Alameda County code–on a case-by-case basis, with the builder convincing the building department of the safety of his or her plans–something no one has yet done, given the lack of quantifiable data.
In Mendocino and Humboldt counties, those rural enclaves of alternative architecture, the code makes experimentation easier with “Class K” permits for owner-builders. The building departments there will approve permits for any owner-built plan signed by an architect. The first cob home to be approved under this code in Mendocino County was designed by John Fordice.
Though easier, this is still a matter of reinventing the wheel for every project. With standards as part of the regular building code, builders could simply follow the recipe and know the result would remain standing–and be legal. That process has moved further along with straw bale construction. Puma County, Arizona, was the first to establish straw bale standards in its building code. Due in part to lobbying by Central Valley rice growers, who needed something to do with rice straw once they were no longer allowed to burn it, the California legislature passed a directive allowing any building department in the state to incorporate the Puma County straw bale code verbatim. Though at this point straw bale construction remains most popular with owner-builders, its incorporation into building codes is moving it slowly into commercial use.
At this experimental stage, a cob house costs about the same as a conventional wood-frame structure–while taking significantly longer to build. If cob standards become part of the building codes, both costs and time will begin to slide. “As soon as the door is open, innovation will proceed like crazy,” John Fordice predicts. “People will evolve more economically competitive ways to do it. We’ll start to build with earth on a large scale, and that will have a big impact on the consumption of the forests.” This year, a toolshed. Next year, a cottage and pond. After that? The world.
