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Natural BuildingNatural building is any building system that places the highest value on sustainability. It is a general term that refers to building that primarily uses natural rather than manufactured materials. The need to lessen the environmental impacts of housing and other buildings while promoting comfortable, healthy, aesthetically pleasing and spiritually uplifting structures is the basis of natural building. To be more sustainable, natural building uses abundantly available, renewable, reused or recycled materials. The use of rapidly renewable materials is increasingly common. Materials The materials common to many types of natural building are clay and sand. When mixed with water and, usually, straw or another fiber, the mixture may form cob or adobe (clay blocks). Cob and adobe are usually made with various mixtures of sand and clay. Other materials commonly used in natural building are: earth (as rammed earth or earth bags), wood (cordwood or timber frame/post-and-beam), straw bales, bamboo and rock. A wide variety of reused or recycled materials are common in natural building. Techniques Each of the major types of natural building will be outlined below, along with the various techniques commonly used. Adobe Main article: Adobe One of the oldest building methods, adobe is simply earth mixed with water. Sometimes chopped straw or other fibers are added for strength. The mixture is then allowed to dry in the desired shape. Usually adobe is shaped into bricks that can be stacked to form walls. Various claims are made about the optimal proportions of clay and sand (or larger agregate). Some say that the best adobe soil contains 15% - 30% clay to bind the material together. Others say equal proportions of clay and sand are best to prevent cracking or fragmenting of the bricks. Sometimes adobe is stabilized with a small amount of cement or asphalt emulsion to provide better weatherproofing. The blocks can either be poured into molds and dried, or pressed into blocks. Adobe colored with clay and polished with natural oil makes an attractive and resilient floor. To protect the walls and reduce maintenance, adobe buildings usually have large overhanging eaves and sizeable foundations. Adobe can be plastered over with cob for both appearance and protection. Adobe has good thermal mass, meaning that it is slow to transmit heat or cold. It is not a good insulator, however, so insulation can be added on the outside, or a double wall built with airspace in between. Cob Main article: Cob The term cob is used for mud building that uses no forms, bricks or wooden framework. Cob building was in use in England prior to the 13th century. Similar forms of mud building have been used in many parts of the world for centuries and date from at least 10,000 years ago. Cob is one of the simplest and least expensive building techniques available. Its other great advantage is its versatility. It can easily be shaped into any form. While cob building died out in England by the late 19th century, thousands of cob structures have endured to the present (20,000 in Devon, alone). It is estimated that from one third to one half of the world's population lives in earthen dwellings today. Cob is used as plaster or filler in several methods of natural building using other materials, such as earth bags, timber frame, cordwood, and straw bales. It is thus the primary ingredient of natural building. Earth bag Earth bag construction is a way of building using burlap or polypropylene bags filled with earth. In recent years, building with earth bags has become one of the most important techniques in natural building. It is a kind of free-form rammed earth. Its growing popularity relates to its use of an abundant and readily available material (earth) in a building technique that is flexible, inexpensive, and easy to use. Timber frame article: Timber frame The essential elements of timber frame building—joined timbers, clay walls and thatch roofs were in place in Europe and Asia by the 9th century. It remained the common mode of house construction in northern cultures until the 19th century. References Kennedy, J., Smith, M. and Wanek, C. eds. 2002. The Art of Natural Building: Design, Construction, Resources. Gabriola Island, BC. [http://www.newsociety.com New Society Publishers. External links
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