 The Inexpensive, Owner Built Cob Home
by Staff Writer
Cob is a mixture of clay soil, straw, water, and often sand that started gaining
popularity in Europe around the 12th century in areas that had limited access to lumber and stone. Extended families or communities
would come together to slowly raise the walls of a new cob home when the need
arose. Because cob buildings utilize local materials and sustainable building
practices, not only will your home be cheap, it will be an environmentally
friendly green home. You'll also be able to escape the cookie-cutter look of
modern suburbs. Many owners choose to implement unique features like built-in
bookcases, ledges, or alcoves into their cob home. Building with cob is so easy
that many people choose to build their own home after taking a few classes and
reading up on the process.
Before you mix your first batch of cob, it is important to pay close attention
to site selection. Depending on climate and temperature, passive solar
architecture can be utilized to maximize heating and cooling efficiency. Proper
design coupled with the high thermal mass of 18 to 24 inch thick walls will
provide a quiet, well-insulated home. Covered porches, long eaves, and overhangs
offer protection from driving rains that could slowly deteriorate cob walls.
Although cob is resistant to water, high nonporous foundations are critical to
protect the base of walls and prevent water infiltration.
The volume of clay in the soil, the quality of the straw, and the quantity of
the sand can affect the quality and strength of your cob. You should make test
batches before beginning work to ensure you are satisfied with the final
product. In days past, cob was mixed by stomping the components together in a
small trench -- or by having oxen do this laborious task. Today, good old foot
power is still preferred by many since it is the greenest option. Tractor
attachments can be used, but many choose to limit carbon emissions by doing as
much work as possible by hand and by using only local materials to build their
cob house.
Mixed cob is formed into loafs or bricks and carried to the foundation. As
additional rows and layers of cobs slowly form the 18- to 24-inch thick walls,
fingers and thumbs are used to squeeze the bricks together and join them into
one interconnected mass. Layers (called lifts) are formed anywhere between a few
inches and a few feet thick around the perimeter of the structure. Lifts are
allowed to dry and cure before subsequent lifts are laid. As a lift is finished,
the internal and external walls are shaved, cut, or scraped to remove excess cob
and provide a clean vertical or tapered wall that will later be plastered.
Each lift needs to cure before applying additional cob. Drying each lift limits
potential damage as the cob slowly shrinks and cracks, and can take between 5
and 14 days. The dried lift is also sturdier and ready to bear the additional
weight of the next lift. Windows, doors, and openings can be formed with wood as
the walls take shape, or a lintel can be placed and the opening carved out
later. Timber is also set into the walls where cabinets, shelves, or anything
requiring a solid anchor will be attached. After the final lift has been set and
cured, a traditional framed roof or living roof
can be applied to protect the newly finished cob walls. Lime sand stucco or
modern stucco can then be applied to interior and exterior walls to protect and
brighten the walls of your new cob home.
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