Cob is a material that consists of sand, straw, earth, water and clay, and has been compared to clay. Cob has a resistance to seismic activity, fireproof, and moderate in price. It is generally used in creating sculptural, artistic forms. The sustainability and eco-building movements began using this method again in recent years.
Cob is a material that has been used for building structures for many centuries. In fact, some accounts date cob to prehistoric times. Afghanistan has the oldest structures made by man using cob and rammed earth. Cob-work goes back as early as the 11th and 12th Centuries. Structures made from cob are found in all climates across the globe. In the U.K., cob is associated with Cornwall and Devon counties in the “West Country”. There are homes in Brittney constructed of cob that have survived over 500 years. To this day, many of these structures are still inhabited.
Many ancient cob buildings are also found in Africa, Wales, the Middle East, as well as some areas in the eastern regions of the United States. There are also many cob cottages that have survived since the mid-19th century in New Zealand.
By tradition, English cob was formulated by mixing sand and clay-based subsoil, along with straw and water. The mixture was ladled onto stone foundations in layers, and then troddened onto walls by the workers. This process is known as the “cobbing process.”
Construction would progress as time allowed, with the need to let the previous day’s work dry and working on another area or wall. After drying, the walls were trimmed and the next application would be built and the doors and windows for the wall would be set in place.
Walls of cob houses were around 24 inches thick, with windows deeply set, giving the homes the appearance of internal character. Cob walls are thick, providing a thermal protection that was easy to warm in summer and winter months. The material has a lifelong span in climates that are rainy if a large overhanging roof was built over the structure.
Modern Cob Buildings
In 1994, Kevin McCabe constructed a four bedroom, 2 story house in England from cob. The house had a reputation for being the first home built out of cob in 70 years. McCabe’s method was mostly traditional. However, he used tractor and sand in his mixture for reducing shrinkage.
From the period of 2002 to 2004, Rob Hopkins constructed his own cob home for his family in the US. The house was the first of its kind in over 100 years. The construction effort was a community project, but was destroyed by arsonists before its completion. The house was ultimately rebuilt in 2010.
There have been a large number of modern cob houses completed as of late, and many more are in the planning stages. Included in the planned cob structures is a public education centre in England.
Some newer cob structures have even won various awards. The “Cob-tun House” in England won the “Royal Institute of British Architects Building of the Year” award in 2005. The construction costs were over $300,000. Only $20,000 of the cost was spent the cob walls used in the construction process. Cob is an alternative and sustainable material that is used for its function and cost effective features.
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