“In many of those countries,” says Conrad Rogue, the founder of the House Alive workshops and author of earthen-construction guidebook House Of Earth, referring to some of the developing nations he’s visited, “building with earth has a stigma of poverty and the olden days.” In the developed world, most notably in the Pacific Northwest region of the United States and in parts of the UK, the opposite reaction is growing. People worldwide are discovering, or rediscovering, a building material that’s cheap, strong, energy-efficient, and capable of producing dramatic, unique structures.
They were standing on it all along.
It’s likely that earthen homes were among the oldest structures ever built by humanity. There are a few different techniques and many names for a building made mostly of, well, dirt, but the one that’s caught on in this recent revival of the material comes from England: Cob.
The etymology of the word “cob” is not really known; it may come from an old word for “strike” or “beat,” which is not dissimilar from the way a cob structure is built, or it’s possible that it may come from a noun that meant something more like “lump.”
Regardless, the ground we stand on, provided it’s a dirt-type ground rather than, say, desert sand or stone, generally includes a topsoil, which is composed of (hopefully) fertile rotted dead things. This is what we think of as dirt. Under that is a layer of what’s called subsoil: denser, darker, older, wetter materials consisting of, usually, sand, silt, and clay. It has the ability to be sculpted when mixed with water and then dries hard, just like cement, but even better—and an estimated third of humanity lives in homes made of subsoil.
There are a few different strategies for constructing homes out of subsoil. Rammed earth, for instance, usually requires that a frame is constructed and a subsoil-water mix poured inside before being very tightly compressed, ideally to about half its original volume. When it dries, the frame is removed. But rammed earth is a very labor-intensive process, requiring brute human strength.
Enter cob. It’s constructed of some kind of subsoil, which must include clay—the percentage doesn’t really matter—sand, water, and fiber. Fiber is the big world-shaking addition. “It has the same function as rebar for concrete,” says Rogue (not his given name, but after 30 years in the U.S., he was tired of Americans mispronouncing his Dutch last name), “but instead of using a few strong strands, like in rebar, you use thousands of weaker strands.”
What makes cob amazing is that you can use, says Rogue, basically anything as a fiber. “In the United States that’s often straw,” he says, “In other countries I’ve seen pine needles or shredded coconut husks or corn husks.”