Questions and answers about cob
At Cob Cottage Company we have found that many visitors and workshop participants
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, and has been lanto's and Linda's
home for 3 years.
Does cob building require an expert?
Absolutely not! Once the basics are understood, 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 can teach 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
course graduates with no previous building experience leave our workshops
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 offers 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 . Our web site
is http://www.cobcottage.com/. We distribute a practical
guide book, The Cobber's Companion and an informative illustrated
reader, Earth Building and the Cob Revival. Our newsletter, the
CobWeb. is available by subscription. To order any of these items,
see our order form.
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Last Modified: December 24, 1997
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