Everything about Cob Material totally explained
Cob is a
building material consisting of
clay,
sand,
straw, water, and
earth, similar to
adobe. Cob is fireproof, resistant to seismic activity, and inexpensive . It can be used to create artistic, sculptural forms and has been revived in recent years by the
natural building and
sustainability movements.
History and usage
Cob is an ancient building material, that has possibly been used for construction since people first began building houses. Cob structures can be found in a variety of climates across the globe; In the UK it's most strongly associated with counties of
Devon and
Cornwall in the
West Country; the
Vale of Glamorgan and
Gower peninsula in Wales;
Donegal Bay in
Ulster and Munster, South-West
Ireland; and
Finisterre in
Brittany where many homes have survived over 500 years and are still inhabited. Many old cob buildings can be found in
Africa, the Middle East,
Wales,
Devon,
Ireland,
Cornwall,
Brittany and some parts of the eastern United States.
Traditionally, English cob was made by mixing the clay-based
subsoil with
straw and
water using
oxen to trample it. The earthen mixture was then ladled onto a stone
foundation in
courses and trodden onto the wall by workers in a process known as
cobbing. The wall height would progress according to how long it took for the last course to dry. After drying, the walls would be trimmed and the next course built, with lintels for later openings such as doors and windows being placed as the wall takes shape.
The walls of a cob house were generally about 24 inches thick, and windows were correspondingly deepset giving the homes a characteristic internal appearance. The thick walls provided excellent thermal mass which was easy to keep warm in winter and cool in summer. Walls with a high thermal mass value act as a temperature fly wheel inside the home. Surprisingly, the material held up really well in rainy climates, so long as a cob house was built with a tall foundation wall and a large roof overhang.
Modern cob buildings
When Kevin McCabe built a two-storey, four bedroom cob house in
England in
1994, it was reputedly the first cob residence built in the country in 70 years. His methods remained very traditional; the only innovations he added were using a
tractor to mix the cob itself, and adding
sand or
shillet (a gravel of crushed shale) to reduce the
shrinkage.
From 2002 to 2004, sustainability enthusiast Rob Hopkins initiated the building of a cob house for his family, the first new one in Ireland in about one hundred years. It was undertaken as a community project, but destroyed by an unknown arsonist shortly before completion.
In 2006, a modern, four-bedroom cob house in
Worcestershire, UK, designed by Associated Architects sold for £745 000. Cobtun House was built in 2001 and won the
Royal Institute of British Architects' Sustainable Building of the Year award in 2005. The total construction cost was £300 000, but the metre-thick cob outer wall cost only £20 000.
In the Pacific Northwest of North America there has been a resurgence of cob building both as an alternative building practice and one desired for its form, function and cost effectiveness. There are more than ten cob houses in the Southern
Gulf Islands of
British Columbia built by Pat Hennebery and the Cobworks workshops.
In 2007, Ann and Gord Baird began constructing a two-storey cob house in
Victoria,
British Columbia for an estimated $210,000 CDN. The 2,150 sq. ft. home includes heated floors, solar panels and a southern exposure for
passive solar heating.
The building process known as "Oregon Cob" is one which was refined by Welsh architect Ianto Evans and researcher Linda Smiley in the 1980s. Oregon Cobb integrates the variation of wall layup technique which uses loaves of mud mixed with sand and straw with a rounded architectural stylism.
Further Information
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