Questions & Answers about Cob
Excerpted from the Introduction
At The Cob Cottage Company, we have found that many visitors and workshop participants have similar questions about cob, as no doubt will many readers. Here are short answers to some of the most common questions.
What Is Cob? Is It Adobe?
Cob is a composite building material, a mixture of earth, clay, sand, straw, and water, hand-worked into monolithic earthen walls. No forms, no cement, no ramming, no machinery. Adobe means sundried earthen bricks, the material they are made of, and the resultant earthen buildings. The word cob comes from an Old English root, meaning "a lump or rounded mass." This term refers to the material itself, to buildings made of it, and to a traditional building technique used for centuries in Europe, in rainy, cold, windy climates as far north as the latitude of Alaska.
Cob is one of many methods for building with raw earth, the world's most common construction material. In simplicity of construction and freedom of design, cob surpasses adobe and related techniques such as rammed earth and compressed earth bricks. 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 much like sculpting with clay. Unlike adobe, cob can easily be built in cool, wet climates such as the Pacific Northwest; its resistance to rain and cold makes cob well suited to all but the coldest parts of America, where it may need additional insulation.
Why Hadn't I Heard of Cob until Recently?
Cob was little known in North America until The Cob Cottage Company reintroduced it in the 1990s. However, the technique was once common in the Southwest, where it was called puddled, coursed, or monolithic adobe. Some early settlers in the Northeast also built with cob. More recently, government regulations have supported the lumber industry's sales needs by not recognizing earth as a suitable building material.
Is Cob Durable? What about in Rainy Places?
In England there are tens of thousands of comfortable cob homes, many of which have been used for more than five centuries. Yemen's medieval 10-story skyscrapers are part cob, as is Taos Pueblo, continuously inhabited for 900 years. A large part of both the Great Pyramid and the Great Wall of China are earth, and the oldest known human dwellings (earthen, of course) in Jericho have survived 9,000 years. So your cob house should easily outlast neighboring studframes, designed for only 50 years' service.
Like any other kind of structure, cob buildings need good roofs and adequate foundations to protect them from water damage. Traditionally, cob walls are protected from driven rain with a lime plaster or stucco, though in protected places in England, unplastered walls have stood for centuries.
Aren't Cob Houses Cold and Damp Inside?
Winter visitors to our cob buildings in the Oregon rain forest often comment on how warm and dry they feel. Cob walls 1 to 2 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, and is ideal for completely unburnable houses in forest fire areas. One of our favorite designs is a cob bench or bed heated by the flue of a wood-burning stove.
What about Earthquakes?
No building system is guaranteed against earthquakes, but cob buildings have a good survival record in seismic zones. Unlike adobe, held together mostly by gravity, cob buildings are locked together by an invisible three-dimensional textile of interwoven straw, with thousands of individual stems giving great overall strength. A cob mansion in Nelson, New Zealand, has survived 150 years in one of the world's most active seismic zones, enduring two major earthquakes without a crack, while the town around it collapsed. The curve and taper characteristic of Oregon cob walls make them even stronger.
Will Cob Make a Normal, Big, Square House?
Absolutely. It can be as big as you need it. But don't sacrifice quality for size. Do you want a work of art or just square footage? Yes, you can make your walls square, but it will cost extra in time, effort, or money. Nature doesn't provide Square; we have to carefully true it up, whether we mill the round tree into square boards or cut round stones square for a rock wall. Earth's yearning to be curved and sculptural gives cob walls an aesthetic quality we can't otherwise easily achieve.
What Does a Cob Cottage Cost?
Cob is one of the least expensive building materials imaginable. Often the soil removed during sitework is enough to build the walls. With inventiveness and forethought, the costs of other components (doors, windows, floors, and so forth) can be extensively reduced. Total building expenses will depend upon size, design, your creativity and organization, and how much you want to be involved. Most of us go to work to pay someone else to build our houses. We also pay for their profit, mistakes, transport, overheads, and bad luck. Above all, we pay loan institutions to borrow their money, then build under their constraints. By being your own builder, you can manufacture your own materials, and by going slowly and carefully, your house could cost one-tenth of what you'd buy one for.
How Fast Can I Build a Cob House?
It takes a long time to make a good house whatever the materials, but in dry weather you could build a two-story wall in a month. A determined owner-builder can move into a modest cob house in less than a year. 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 drywall, tape, spackling, sanding, painting, sheathing, or vapor barriers. Yet racing to build fast is missing the whole 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 faster, easier, and more enjoyable with a team, so it lends itself to community projects, building parties, and workshops.
What about Building Codes?
Codes today protect the corporate 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 few problems. Legally permitted cob buildings are beginning to appear, but there is considerable expense and paperwork involved, as with any permit. You have several alternatives to these inconveniences; see appendix 2.
Can I Find a Competent Builder?
With cob construction now a decade old in North America, professional contractors are beginning to appear. We keep a roster at the Cob Cottage Company; contact us. But rather than hiring a builder, consider building for yourself. If you are personally involved, you'll likely get a better job. Many cob builders we know are middle-aged or elderly, or are women. You don't need expensive equipment lengthy training to learn the basics of this friendly, safe, and forgiving medium.
How Can I Learn More about Cob?
- The only proven way to learn about cob building is to try it!
- The Cob Cottage Company offers hands-on construction workshops in most parts of North America. Cob building is amazingly simple. In a week-long workshop, you can learn how to select materials, prepare a mix, and build a wall. We have taught men, women, and children of all ages and abilities everything needed to build cob parts of a small cottage, including site selection, foundations, windows and doors, floors, attachment to wood and other materials, detail work, and finishing. Course graduates with no previous building experience leave feeling confident and enthusiastic about building their own cob cottage.
- At the new North American School of Natural Building in the rain forest of southwest Oregon, we sponsor training in cob and other aspects of natural building, including roundwood carpentry, natural plasters, earthen flooring, passive solar design and siting, earth stoves and built-in furniture, living roofs, etc.
- For those serious about a livelihood in natural building, apprenticeships are available with a year-long certificate program. Contact us for our current schedule, or check our visually inspiring Web site at www.deatech.com/cobcottage/.
- We supply videos and slides of finished cob buildings, The Cobber's Companion (a step-by-step, how-to-do-it manual), Earth Building and the Cob Revival (an informative illustrated reader), and other literature.
- The Cob Web, the only newsletter mostly devoted to cob, is available by subscription.
- We are available for public sideshows and demonstrations.