Cob (building)
Encyclopedia
Building material
Building material is any material which is used for a construction purpose. Many naturally occurring substances, such as clay, sand, wood and rocks, even twigs and leaves have been used to construct buildings. Apart from naturally occurring materials, many man-made products are in use, some more...
consisting of clay
Clay
Clay is a general term including many combinations of one or more clay minerals with traces of metal oxides and organic matter. Geologic clay deposits are mostly composed of phyllosilicate minerals containing variable amounts of water trapped in the mineral structure.- Formation :Clay minerals...
, sand
Sand
Sand is a naturally occurring granular material composed of finely divided rock and mineral particles.The composition of sand is highly variable, depending on the local rock sources and conditions, but the most common constituent of sand in inland continental settings and non-tropical coastal...
, straw
Straw
Straw is an agricultural by-product, the dry stalks of cereal plants, after the grain and chaff have been removed. Straw makes up about half of the yield of cereal crops such as barley, oats, rice, rye and wheat. It has many uses, including fuel, livestock bedding and fodder, thatching and...
, water, and earth
Soil
Soil is a natural body consisting of layers of mineral constituents of variable thicknesses, which differ from the parent materials in their morphological, physical, chemical, and mineralogical characteristics...
, similar to adobe
Adobe
Adobe is a natural building material made from sand, clay, water, and some kind of fibrous or organic material , which the builders shape into bricks using frames and dry in the sun. Adobe buildings are similar to cob and mudbrick buildings. Adobe structures are extremely durable, and account for...
. 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
Natural building
A natural building involves a range of building systems and materials that place major emphasis on sustainability. Ways of achieving sustainability through natural building focus on durability and the use of minimally processed, plentiful or renewable resources, as well as those that, while...
and sustainability
Sustainability
Sustainability is the capacity to endure. For humans, sustainability is the long-term maintenance of well being, which has environmental, economic, and social dimensions, and encompasses the concept of union, an interdependent relationship and mutual responsible position with all living and non...
movements.
History and usage
Rammed earth
Rammed earth, also known as taipa , tapial , and pisé , is a technique for building walls using the raw materials of earth, chalk, lime and gravel. It is an ancient building method that has seen a revival in recent years as people seek more sustainable building materials and natural building methods...
and cob. Cobwork (tabya) was used in the Maghreb
Maghreb
The Maghreb is the region of Northwest Africa, west of Egypt. It includes five countries: Morocco, Algeria, Tunisia, Libya, and Mauritania and the disputed territory of Western Sahara...
and al-Andalus
Al-Andalus
Al-Andalus was the Arabic name given to a nation and territorial region also commonly referred to as Moorish Iberia. The name describes parts of the Iberian Peninsula and Septimania governed by Muslims , at various times in the period between 711 and 1492, although the territorial boundaries...
in the 11th and 12th centuries and was described in detail by Ibn Khaldun
Ibn Khaldun
Ibn Khaldūn or Ibn Khaldoun was an Arab Tunisian historiographer and historian who is often viewed as one of the forerunners of modern historiography, sociology and economics...
in the 14th century.
Cob structures can be found in a variety of climates across the globe; In the UK it is most strongly associated with counties of Devon
Devon
Devon is a large county in southwestern England. The county is sometimes referred to as Devonshire, although the term is rarely used inside the county itself as the county has never been officially "shired", it often indicates a traditional or historical context.The county shares borders with...
and Cornwall
Cornwall
Cornwall is a unitary authority and ceremonial county of England, within the United Kingdom. It is bordered to the north and west by the Celtic Sea, to the south by the English Channel, and to the east by the county of Devon, over the River Tamar. Cornwall has a population of , and covers an area of...
in the West Country
West Country
The West Country is an informal term for the area of south western England roughly corresponding to the modern South West England government region. It is often defined to encompass the historic counties of Cornwall, Devon, Dorset and Somerset and the City of Bristol, while the counties of...
; the Vale of Glamorgan
Vale of Glamorgan
The Vale of Glamorgan is a county borough in Wales; an exceptionally rich agricultural area, it lies in the southern part of Glamorgan, South Wales...
and Gower Peninsula
Gower Peninsula
Gower or the Gower Peninsula is a peninsula in south Wales, jutting from the coast into the Bristol Channel, and administratively part of the City and County of Swansea. Locally it is known as "Gower"...
in Wales; Donegal Bay
Donegal Bay
Donegal Bay is an inlet in the northwest of Ireland. Three counties – Donegal to the north and west, Leitrim and Sligo to the south – have shorelines on the bay, which is bounded on the west by the Atlantic Ocean...
in Ulster
Ulster
Ulster is one of the four provinces of Ireland, located in the north of the island. In ancient Ireland, it was one of the fifths ruled by a "king of over-kings" . Following the Norman invasion of Ireland, the ancient kingdoms were shired into a number of counties for administrative and judicial...
and Munster, South-West Ireland
Ireland
Ireland is an island to the northwest of continental Europe. It is the third-largest island in Europe and the twentieth-largest island on Earth...
; and Finisterre
Finisterre
Finisterre, Finisterra, Fisterra, or Finistère may refer to:Places* Cape Finisterre , headland in Galicia, north-west Spain, the Southern landfall of the Bay of Biscay...
in Brittany
Brittany
Brittany is a cultural and administrative region in the north-west of France. Previously a kingdom and then a duchy, Brittany was united to the Kingdom of France in 1532 as a province. Brittany has also been referred to as Less, Lesser or Little Britain...
where many homes have survived over 500 years and are still inhabited. Many old cob buildings can be found in Africa
Africa
Africa is the world's second largest and second most populous continent, after Asia. At about 30.2 million km² including adjacent islands, it covers 6% of the Earth's total surface area and 20.4% of the total land area...
, the Middle East, Wales
Wales
Wales is a country that is part of the United Kingdom and the island of Great Britain, bordered by England to its east and the Atlantic Ocean and Irish Sea to its west. It has a population of three million, and a total area of 20,779 km²...
, Devon
Devon
Devon is a large county in southwestern England. The county is sometimes referred to as Devonshire, although the term is rarely used inside the county itself as the county has never been officially "shired", it often indicates a traditional or historical context.The county shares borders with...
, Cornwall
Cornwall
Cornwall is a unitary authority and ceremonial county of England, within the United Kingdom. It is bordered to the north and west by the Celtic Sea, to the south by the English Channel, and to the east by the county of Devon, over the River Tamar. Cornwall has a population of , and covers an area of...
, Brittany
Brittany
Brittany is a cultural and administrative region in the north-west of France. Previously a kingdom and then a duchy, Brittany was united to the Kingdom of France in 1532 as a province. Brittany has also been referred to as Less, Lesser or Little Britain...
and some parts of the eastern United States. A number of cob cottages survive from mid-19th century New Zealand.
Traditionally, English cob was made by mixing the clay-based subsoil
Subsoil
Subsoil, or substrata, is the layer of soil under the topsoil on the surface of the ground. The subsoil may include substances such as clay and/or sand that has only been partially broken down by air, sunlight, water, wind etc., to produce true soil...
with sand, straw
Straw
Straw is an agricultural by-product, the dry stalks of cereal plants, after the grain and chaff have been removed. Straw makes up about half of the yield of cereal crops such as barley, oats, rice, rye and wheat. It has many uses, including fuel, livestock bedding and fodder, thatching and...
and water
Water
Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...
using oxen to trample it. The earthen mixture was then ladled onto a stone foundation
Foundation (architecture)
A foundation is the lowest and supporting layer of a structure. Foundations are generally divided into two categories: shallow foundations and deep foundations.-Shallow foundations:...
in courses
Course (architecture)
A course is a continuous horizontal layer of similarly-sized building material one unit high, usually in a wall. The term is almost always used in conjunction with unit masonry such as brick, cut stone, or concrete masonry units .-Styles:...
and trodden onto the wall by workers in a process known as cobbing. The construction would progress according to the time required for the prior 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 deep-set, 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 thermal buffer inside the home. The material has a long life span even in rainy climates, provided a tall foundation and large roof overhang are present.
Modern cob buildings
England
England is a country that is part of the United Kingdom. It shares land borders with Scotland to the north and Wales to the west; the Irish Sea is to the north west, the Celtic Sea to the south west, with the North Sea to the east and the English Channel to the south separating it from continental...
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
Tractor
A tractor is a vehicle specifically designed to deliver a high tractive effort at slow speeds, for the purposes of hauling a trailer or machinery used in agriculture or construction...
to mix the cob itself, and adding sand
Sand
Sand is a naturally occurring granular material composed of finely divided rock and mineral particles.The composition of sand is highly variable, depending on the local rock sources and conditions, but the most common constituent of sand in inland continental settings and non-tropical coastal...
or shillet (a gravel of crushed shale) to reduce the shrinkage
Shrinkage
Shrinkage has multiple meanings, depending on the context.* Shrinkage – the loss of products* Shrinkage – a technique to improve an estimator* Shrinkage – a common problem when doing laundry...
.
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. This house, located at The Hollies Centre for Practical Sustainability in County Cork, is being rebuilt (2010). There are also a number of other modern cob houses completed and more planned including a public education centre.
In 2000-2001, a modern, four-bedroom cob house in Worcestershire
Worcestershire
Worcestershire is a non-metropolitan county, established in antiquity, located in the West Midlands region of England. For Eurostat purposes it is a NUTS 3 region and is one of three counties that comprise the "Herefordshire, Worcestershire and Warwickshire" NUTS 2 region...
, UK designed by Associated Architects
Associated Architects
thumb|right|Associated Architects' Offices at [[The Mailbox]], Birminghamthumb|right|RIBA Award Winner 2009, David Wilson LibraryAssociated Architects is a leading architectural firm based in Birmingham, England. The practice has a broad portfolio of work including arts, commercial offices, housing...
was sold for £999,000. Cobtun House was built in 2001 and won the Royal Institute of British Architects
Royal Institute of British Architects
The Royal Institute of British Architects is a professional body for architects primarily in the United Kingdom, but also internationally.-History:...
' 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 the US 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
Gulf Islands
The Gulf Islands are the islands in the Strait of Georgia , between Vancouver Island and the mainland of British Columbia, Canada....
of British Columbia
British Columbia
British Columbia is the westernmost of Canada's provinces and is known for its natural beauty, as reflected in its Latin motto, Splendor sine occasu . Its name was chosen by Queen Victoria in 1858...
built by Pat Hennebery, Tracy Calvert, Elke Cole and the Cobworks workshops.
In 2007, Ann and Gord Baird began constructing a two-story cob house in Victoria
Victoria, British Columbia
Victoria is the capital city of British Columbia, Canada and is located on the southern tip of Vancouver Island off Canada's Pacific coast. The city has a population of about 78,000 within the metropolitan area of Greater Victoria, which has a population of 360,063, the 15th most populous Canadian...
, British Columbia
British Columbia
British Columbia is the westernmost of Canada's provinces and is known for its natural beauty, as reflected in its Latin motto, Splendor sine occasu . Its name was chosen by Queen Victoria in 1858...
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 Cob integrates the variation of wall layup technique which uses loaves of mud mixed with sand and straw with a rounded architectural stylism.
See also
|
Mudbrick A mudbrick is a firefree brick, made of a mixture of clay, mud, sand, and water mixed with a binding material such as rice husks or straw. They use a stiff mixture and let them dry in the sun for 25 days.... Rammed earth Rammed earth, also known as taipa , tapial , and pisé , is a technique for building walls using the raw materials of earth, chalk, lime and gravel. It is an ancient building method that has seen a revival in recent years as people seek more sustainable building materials and natural building methods... Rice-hull bagwall construction Rice-hull bagwall construction is a system of building, with results aesthetically similar to the use of earthbag or cob construction, in which woven polypropylene bags are tightly filled with raw rice-hulls, and these are stacked up, layer upon layer, with strands of four-pronged barbed wire... Sod Sod or turf is grass and the part of the soil beneath it held together by the roots, or a piece of thin material.The term sod may be used to mean turf grown and cut specifically for the establishment of lawns... Sod house The sod house or "soddy" was a corollary to the log cabin during frontier settlement of Canada and the United States. The prairie lacked standard building materials such as wood or stone; however, sod from thickly-rooted prairie grass was abundant... Straw-bale construction Straw-bale construction is a building method that uses bales of straw as structural elements, building insulation, or both... Super Adobe Superadobe is a form of earthbag construction that was developed by Iranian architect Nader Khalili. The technique uses layered long fabric tubes or bags filled with adobe to form a compression structure. The resulting beehive shaped structures employs arches, domes, and vaults to create single and... Woodway House Woodway House is in Teignmouth, South Devon, England. It was at one time a farm on lands held by the Bishops of Exeter. In around 1815 a thatched 'cottage' in the 'cottage orne' style of Horace Walpole's Thames-side villa, Strawberry Hill, was built here by Captain James Spratt R.N.Walpole built... A typical Devon cob building |
Further reading
- Building With Cob, A Step by Step Guide by Adam Weismann and Katy Bryce. Published by Green Books ; 2006, ISBN 1-903998-727.
- The Hand-Sculpted House: A Philosophical and Practical Guide to Building a Cob Cottage (The Real Goods Solar Living Book) by Ianto Evans, Michael G. Smith, Linda Smiley, Deanne Bednar (Illustrator), Chelsea Green Publishing Company; (June 2002), ISBN 1-890132-34-9.
- The Cob Builders Handbook: You Can Hand-Sculpt Your Own Home by Becky Bee, Groundworks, 1997 ISBN 9780965908207