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Cob building is one of the oldest building techniques and has been used for thousands of years. The materials used are earth, straw, sand and water which are then mixed either mechanically or by hand. This mixture is then formed into 'cobs' (lumps of material) which are then pressed together to form the walls of the structure. Once dried the cobs become very strong and durable.
Cob has many advantages for green building. The material for building can normally be sourced locally. Earth can be used from around the site and the aggregate (straw, sand etc.) can include recycled materials such as concrete. The use of all natural and sustainable materials greatly reduces the carbon expended and energy used during construction, even on site construction is mostly by non-mechanical means.
Cob is load bearing and does not require any framework. This saves on using lumber. Cob walls are generally much thicker than standard brick and mortar walls - often up to 24 inches. This gives them better sound absorption and a greater thermal mass. The thermal mass (how well a material soaks up heat) of cob is far superior to normal house brick, allowing the building to store heat during the day and release it slowly at night when it is colder. This reduces the amount of heat that a heating system needs to generate.
Whilst cob building may seem a primitive and outdated technique in the modern era it is enjoying a revival due to its benefits for the environment and design. Cob is much easier to shape and sculpt then other materials. In 2005 Cobtun House (a four bedroom cob house built in 2001) in Worcestershire won the Royal Institute of British Architects' Sustainable Building of the Year award and was later sold in 2007 for 750,000 GBP.
Cob building is also becoming seen as a viable alternative in other industrialised nations such as America, Canada and New Zealand where dryer climates lend themselves to cob construction.
When considering using cob as a building material it is important to take into account local weather conditions. In a rainy climate such as the UK it is important to integrate rain protection. The easiest way is to allow more of an overhang on the roof. This lends itself to green building as extra roof space can be used for rain collection, solar heating and green roofing.
Acquiring planning permission for a cob building is the same as a building made from more conventional materials and should not affect the application. Building with cob can also be preferably in the eyes of planning authorities.
The Planning Policy Guidance Notices (PPGs) set out by authorities may help cob buildings gain permission over more conventional buildings (this is dealt with in PPG12 and PPG15). The UK government is also in the process of a major push towards sustainable construction (PPG1) and as cob is one of the world's most abundant and sustainable building materials it may be looked upon favourably when putting in an application.