The Inexpensive, Owner Built Cob Home
 Cob is a mixture of clay soil, straw, water, and often sand
that started
gaining popularity in Europe around the 12th century since some areas
had limited access to lumber and stone. Extended families or communities would come
together to slowly raise the walls of a new cob home as the need arose. Since 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 will
also be able to escape the cookie cutter look of modern suburbs since 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 portent to pay close attention to
site selection. Depending on climate and temperature passive solar architecture
can be utilized to maximum 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 will 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, or the quantity of the sand
can affect the quality and strength of your cob so you should make test batches
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 using only local materials
in 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 joining 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 may 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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