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Building a cob wall for an owner built homeThe 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.

Inexpensive owner built cob home 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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