Questions and Answers About Cob

At Cob Cottage Company we have found that many visitors have similar questions about cob. Here are some of the most common questions.

What is cob?

The word cob comes from an Old English root meaning "a lump or rounded mass". It's a traditional building technique using hand formed lumps of earth mixed with sand and straw. Cob is easy to learn and inexpensive to build. It dries to a hardness similar to lean concrete and is used like adobe to create self supporting, load bearing walls. Cob has been used for centuries throughout Western Europe, even in rainy and windy climates, as far north as the latitude of Alaska. This ancient technology doesn't contribute to deforestation, pollution or mining, nor depend on manufactured materials or power tools. Cob is nontoxic and completely recyclable, which is important in this era of environmental degradation, dwindling natural resources and chemical contaminants.

How is cob different from adobe?

Cob is one of many methods for building with raw earth, the world's commonest construction material. It surpasses related techniques such as adobe, rammed earth pise, and compressed earth bricks both in ease of construction and freedom of design. Since you don't need straight forms or rectilinear molds, cob lends itself to organic shapes: curved walls, arches and vaults. Building with cob is a sensory and aesthetic experience like sculpting with clay. You can add on, cut out, or reshape at any time, even after the cob is dry. Unlike adobe, cob can be built in cool damp climates like the Pacific Northwest: its resistance to rain and cold makes cob well suited in all but the coldest parts of America.

Why haven't I heard of cob before?

Cob is a recent arrival in the United States. Except for adobe in the Southwest, earthen building is virtually unknown here. In other parts of the world, cob and similar techniques have been popular for millennia. Throughout Western Europe, many of the picturesque stuccoed or whitewashed buildings are actually made of cob. In England there are tens of thousands of comfortable cob homes, many of which have been continuously inhabited for over 500 years. The durability and comfort of these valuable houses has sparked a renaissance in traditional cob centers such as Devon, where cob homes are again being built.

Why doesn't it wash away in the rain?

Cob is very resistant to weathering. Because of its porous nature, it withstands long periods of rain without weakening. However, too much exposure is best avoided by the "boots and cap" strategy: wide roof eaves to protect the walls and an impervious foundation. In windy areas a lime-sand plaster is traditionally used to protect exterior cob walls.

What about earthquakes?

No building system is earthquake proof under every seismic condition, but part of the Great Pyramids and the Great Wall of China are made of earth. The oldest inhabited structure in the U.S., Taos Pueblo, is earthen construction. A cob mansion in Nelson, New Zealand has survived without a crack, two major earthquakes which destroyed the town around it. In South Yemen, in a fault zone, there are Medieval earthen houses 13 stories high. Since a cob building is one monolithic unit reinforced by straw, it has no weak straight-line mortar joints, making it stronger than brick or block. The curve and taper we give "Oregon cob" walls make them even stronger.

Isn't it cold and damp inside?

Winter visitors to our cob buildings in Oregon often comment on how warm and dry they feel. Cob walls one to two feet thick provide immense thermal mass and adequate insulation, ideal for passive solar construction. Cob structures require little additional heating in winter and remain cool and comfortable on hot summer days. As it is fireproof, cob can be used for building ovens, stoves and chimneys. One of our favorite designs is a cob bench or bed heated by the flue of a wood burning stove.

How fast can I build with cob?

The rate of building depends on weather and the size of your workforce; in dry weather we build up to a foot of height per day. In wood construction, the frame is a tiny part of the work, but a cob wall once built is finished apart from the plaster. Pipes and wires are laid directly in place and there's no need for sheet rock, tape, spackling, sanding, painting, sheathing, or vapor barriers. But racing to build fast is missing the point and half the fun. Unlike conventional modern building with its frenetic pace, power tools, and scope for errors and accidents, cob-making is a peaceful, meditative and rhythmic exercise. Building cob is easier and more enjoyable with a crew, so it lends itself to community projects, building parties and workshops.

What about building codes?

Codes today protect the industrial manufacturers of building components better than homeowners. Not surprisingly, there is no code for cob, though nowhere is earthen building prohibited. Many cob builders choose not to involve building officials and have had no problems. Legally permitted cob buildings are beginning to appear; there's considerable expense and paperwork involved, as with any permit.

What does a cob cottage cost?

Cob is one of the cheapest building materials imaginable. Often the soil removed during site work is enough to build the walls. The owner-builder can supply the labor, inviting friends to join in the excitement of hand sculpting a house. With inventiveness and forethought, the costs of other components (doors, windows, roof, floors, etc.) can be extensively reduced. The Cob Cottage Company works primarily with recycled materials and handwork lumber. Using local materials such as poles, bamboo, stone, and cedar shakes, our second cottage was completed for $500.

Does cob building require an expert?

Absolutely not! Once the basics are understood, cob building is amazingly simple. In a week you can learn how to select materials, prepare a mix, and build a wall. We can show you everything you need to build your cob cottage: site selection, foundations, windows and doors, attachment of wood and other materials, detail work and finishing. Many with no previous building experience leave our complex feeling confident and enthusiastic about building their own cob cottage.

How can I learn more about cob?

The only proven way to learn about cob building is to try it. The Cob Cottage Company is now offering hands-on cob construction workshops in most parts of North America. Contact us for our current schedule. We also supply videos and slides of finished cob buildings .