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Cob, cobb, or clom (in Wales) is a natural
building material Building material is material used for construction. Many naturally occurring substances, such as clay, rocks, sand, wood, and even twigs and leaves, have been used to construct buildings. Apart from naturally occurring materials, many man-m ...
made from
subsoil Subsoil is the layer of soil under the topsoil on the surface of the ground. Like topsoil, it is composed of a variable mixture of small particles such as sand, silt and clay, but with a much lower percentage of organic matter and humus, and it ...
, water, fibrous
organic material Organic matter, organic material, or natural organic matter refers to the large source of carbon-based compounds found within natural and engineered, terrestrial, and aquatic environments. It is matter composed of organic compounds that have ...
(typically
straw Straw is an agricultural byproduct consisting of the dry stalks of cereal plants after the grain and chaff have been removed. It makes up about half of the yield of cereal crops such as barley, oats, rice, rye and wheat. It has a num ...
), and sometimes
lime Lime commonly refers to: * Lime (fruit), a green citrus fruit * Lime (material), inorganic materials containing calcium, usually calcium oxide or calcium hydroxide * Lime (color), a color between yellow and green Lime may also refer to: Botany ...
. The contents of subsoil vary, and if it does not contain the right mixture, it can be modified with sand or clay. Cob is fireproof, resistant to seismic activity, and uses low-cost materials, although it is very labour intensive. It can be used to create artistic and sculptural forms, and its use has been revived in recent years by the natural building and
sustainability Specific definitions of sustainability are difficult to agree on and have varied in the literature and over time. The concept of sustainability can be used to guide decisions at the global, national, and individual levels (e.g. sustainable livin ...
movements. In technical building and engineering documents, such as the Uniform Building Code of the western USA, cob may be referred to as "unburned clay masonry," when used in a structural context. It may also be referred to as "aggregate" in non-structural contexts, such as "clay and sand aggregate," or more simply "organic aggregate," such as where cob is a filler between post and beam construction.


History and usage

''Cob'' is an English term attested to around the year 1600 for an ancient building material that has been used for building since prehistoric times. The etymology of ''cob'' and ''cobbing'' is unclear, but in several senses means to ''beat'' or ''strike'', which is how cob material is applied to a wall. Cob material is known by many names including ''
adobe Adobe ( ; ) is a building material made from earth and organic materials. is Spanish for ''mudbrick''. In some English-speaking regions of Spanish heritage, such as the Southwestern United States, the term is used to refer to any kind of ...
'',Rapp, George Robert. "Unbaked clay or mud", ''Archaeomineralogy''. 2nd ed. Berlin: Springer, 2009. Print. ''lump clay'', '' puddled clay'', ''chalk mud'', ''
wychert Wychert or witchert (with a number of variant spellings existing and meaning "white earth") is a natural blend of white chalk and clay which is mixed with straw to make walls and buildings, usually then thatched or topped with red clay tiles. ...
'', ''clay daubins'', ''swish'' (
Asante Twi Asante, also known as Ashanti, Ashante, or Asante Twi, is one of the principal members of the Akan dialect continuum. It is one of the four mutually intelligible dialects of Akan which are collectively known as Twi, the others being Bono and A ...
), ''torchis'' (French),Edwards, Jay Dearborn, and Nicolas Verton. "mud with straw", ''A Creole Lexicon Architecture, Landscape, People''. Baton Rouge: Louisiana State UP, 2004. Print. ''bauge'' (French), ''bousille'' (French mud with moss), and ''cat and clay''. Cob structures can be found in a variety of climates across the globe. European examples include: * in England, notably in the counties of
Devon Devon ( , historically known as Devonshire , ) is a ceremonial and non-metropolitan county in South West England. The most populous settlement in Devon is the city of Plymouth, followed by Devon's county town, the city of Exeter. Devon i ...
and
Cornwall Cornwall (; kw, Kernow ) is a historic county and ceremonial county in South West England. It is recognised as one of the Celtic nations, and is the homeland of the Cornish people. Cornwall is bordered to the north and west by the Atlantic ...
in the
West Country The West Country (occasionally Westcountry) is a loosely defined area of South West England, usually taken to include all, some, or parts of the counties of Cornwall, Devon, Dorset, Somerset, Bristol, and, less commonly, Wiltshire, Gloucest ...
, and in
East Anglia East Anglia is an area in the East of England, often defined as including the counties of Norfolk, Suffolk and Cambridgeshire. The name derives from the Anglo-Saxon kingdom of the East Angles, a people whose name originated in Anglia, in w ...
(where it is referred to as ''clay lump'') * in Wales, notably in rural
Anglesey Anglesey (; cy, (Ynys) Môn ) is an island off the north-west coast of Wales. It forms a principal area known as the Isle of Anglesey, that includes Holy Island across the narrow Cymyran Strait and some islets and skerries. Anglesey isla ...
* in Donegal Bay in
Ulster Ulster (; ga, Ulaidh or ''Cúige Uladh'' ; sco, label= Ulster Scots, Ulstèr or ''Ulster'') is one of the four traditional Irish provinces. It is made up of nine counties: six of these constitute Northern Ireland (a part of the United Ki ...
and in Munster, South-West
Ireland Ireland ( ; ga, Éire ; Ulster-Scots: ) is an island in the North Atlantic Ocean, in north-western Europe. It is separated from Great Britain to its east by the North Channel, the Irish Sea, and St George's Channel. Ireland is the s ...
* in Finisterre and Ille-et-Vilaine in
Brittany Brittany (; french: link=no, Bretagne ; br, Breizh, or ; Gallo: ''Bertaèyn'' ) is a peninsula, historical country and cultural area in the west of modern France, covering the western part of what was known as Armorica during the period ...
, where many homes have survived over 500 years and are still inhabited Some of the oldest human-made structures in Afghanistan are composed of
rammed earth Rammed earth is a technique for constructing foundations, floors, and walls using compacted natural raw materials such as earth, chalk, lime, or gravel. It is an ancient method that has been revived recently as a sustainable building method. ...
and cob. Cobwork (''tabya'') was used in the
Maghreb The Maghreb (; ar, الْمَغْرِب, al-Maghrib, lit=the west), also known as the Arab Maghreb ( ar, المغرب العربي) and Northwest Africa, is the western part of North Africa and the Arab world. The region includes Algeria, ...
and
al-Andalus Al-Andalus translit. ; an, al-Andalus; ast, al-Ándalus; eu, al-Andalus; ber, ⴰⵏⴷⴰⵍⵓⵙ, label=Berber, translit=Andalus; ca, al-Àndalus; gl, al-Andalus; oc, Al Andalús; pt, al-Ândalus; es, al-Ándalus () was the Mus ...
in the 11th and 12th centuries, and was described in detail by
Ibn Khaldun Ibn Khaldun (; ar, أبو زيد عبد الرحمن بن محمد بن خلدون الحضرمي, ; 27 May 1332 – 17 March 1406, 732-808 AH) was an Arab The Historical Muhammad', Irving M. Zeitlin, (Polity Press, 2007), p. 21; "It is, of ...
in the 14th century. Many old cob buildings can be found in
Africa Africa is the world's second-largest and second-most populous continent, after Asia in both cases. At about 30.3 million km2 (11.7 million square miles) including adjacent islands, it covers 6% of Earth's total surface area ...
, the Middle East, and the southwestern United States like the
Taos Pueblo Taos Pueblo (or Pueblo de Taos) is an ancient pueblo belonging to a Taos-speaking (Tiwa) Native American tribe of Puebloan people. It lies about north of the modern city of Taos, New Mexico. The pueblos are considered to be one of the olde ...
. A number of cob cottages survive from mid-19th-century New Zealand.Dozens of cob cottages ar
listed on the Register
of the New Zealand Historic Places Trust, e.g.
Traditionally, English cob was made by mixing the clay-based subsoil with sand, straw and water using
oxen An ox ( : oxen, ), also known as a bullock (in BrE, AusE, and IndE), is a male bovine trained and used as a draft animal. Oxen are commonly castrated adult male cattle; castration inhibits testosterone and aggression, which makes the m ...
to trample it. English soils contain varying amounts of
chalk Chalk is a soft, white, porous, sedimentary carbonate rock. It is a form of limestone composed of the mineral calcite and originally formed deep under the sea by the compression of microscopic plankton that had settled to the sea floor. Cha ...
, and cob made with significant amounts of chalk are called ''chalk cob'' or ''
wychert Wychert or witchert (with a number of variant spellings existing and meaning "white earth") is a natural blend of white chalk and clay which is mixed with straw to make walls and buildings, usually then thatched or topped with red clay tiles. ...
''. The earthen mixture was then ladled onto a stone
foundation Foundation may refer to: * Foundation (nonprofit), a type of charitable organization ** Foundation (United States law), a type of charitable organization in the U.S. ** Private foundation, a charitable organization that, while serving a good cause ...
in courses 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 are generally about 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 and/or humid climates, provided a tall foundation and large roof overhang are present. Cob is
fireproof Fireproofing is rendering something (structures, materials, etc.) resistant to fire, or incombustible; or material for use in making anything fire-proof. It is a passive fire protection measure. "Fireproof" or "fireproofing" can be used as a n ...
, while "fire cob" (cob without straw or fiber) is a
refractory material In materials science, a refractory material or refractory is a material that is resistant to decomposition by heat, pressure, or chemical attack, and retains strength and form at high temperatures. Refractories are polycrystalline, polyphase ...
(the same material, essentially, as unfired common red brick), and historically, has been used to make chimneys, fireplaces, forges and crucibles. Without fiber, however, cob loses most of its tensile strength.


Modern cob buildings

When Kevin McCabe constructed a two-story, four bedroom cob house in
England England is a Countries of the United Kingdom, country that is part of the United Kingdom. It shares land borders with Wales to its west and Scotland to its north. The Irish Sea lies northwest and the Celtic Sea to the southwest. It is separa ...
, UK in 1994, it was reputedly the first cob residence built in the country in 70 years. His techniques remained very traditional; the only innovations he made were using a
tractor A tractor is an engineering vehicle specifically designed to deliver a high tractive effort (or torque) at slow speeds, for the purposes of hauling a Trailer (vehicle), trailer or machinery such as that used in agriculture, mining or construc ...
to mix the cob and adding sand or shillet, a gravel of crushed
shale Shale is a fine-grained, clastic sedimentary rock formed from mud that is a mix of flakes of clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4) and tiny fragments ( silt-sized particles) of other minerals, especial ...
, to reduce shrinkage. From 2002 to 2004, sustainability enthusiast Rob Hopkins initiated the construction of a cob house for his family, the first new one in
Ireland Ireland ( ; ga, Éire ; Ulster-Scots: ) is an island in the North Atlantic Ocean, in north-western Europe. It is separated from Great Britain to its east by the North Channel, the Irish Sea, and St George's Channel. Ireland is the s ...
in circa one hundred years. It was a community project, but an unidentified
arsonist Arson is the crime of willfully and deliberately setting fire to or charring property. Although the act of arson typically involves buildings, the term can also refer to the intentional burning of other things, such as motor vehicles, water ...
destroyed it shortly before completion. The house, located at The Hollies Centre for Practical Sustainability in
County Cork County Cork ( ga, Contae Chorcaí) is the largest and the southernmost county of Ireland, named after the city of Cork, the state's second-largest city. It is in the province of Munster and the Southern Region. Its largest market towns ar ...
, was being rebuilt as of 2010. There are a number of other completed modern cob houses and more are planned, including a public education centre. In 2000-01, a modern, four bedroom cob house in
Worcestershire Worcestershire ( , ; written abbreviation: Worcs) is a Counties of England, county in the West Midlands (region), West Midlands of England. The area that is now Worcestershire was absorbed into the unified Kingdom of England in 927, at which ...
,
England England is a Countries of the United Kingdom, country that is part of the United Kingdom. It shares land borders with Wales to its west and Scotland to its north. The Irish Sea lies northwest and the Celtic Sea to the southwest. It is separa ...
, UK, designed by
Associated Architects Associated Architects' Birmingham Offices are located in The Mailbox, which was designed by the practice RIBA Award Winner 2009, David Wilson Library Associated Architects is a leadinAJ100architectural firm with offices in Birmingham and Lee ...
, was sold for £999,000. Cobtun House was erected in 2001 and won the
Royal Institute of British Architects The Royal Institute of British Architects (RIBA) is a professional body for architects primarily in the United Kingdom, but also internationally, founded for the advancement of architecture under its royal charter granted in 1837, three supp ...
' Sustainable Building of the Year award in 2005. The total construction cost was £300,000, but the metre-thick outer cob wall cost only £20,000. In the Pacific Northwest of the
United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territo ...
there has been a resurgence of cob construction, both as an alternative building practice and one desired for its form, function, and cost effectiveness. Pat Hennebery, Tracy Calvert, Elke Cole, and the Cobworks workshops erected more than ten cob houses in the Southern
Gulf Islands The Gulf Islands are a group of islands in the Salish Sea between Vancouver Island and the mainland coast of British Columbia. Etymology The name "Gulf Islands" comes from " Gulf of Georgia," the original term used by George Vancouver in his ma ...
of
British Columbia British Columbia (commonly abbreviated as BC) is the westernmost province of Canada, situated between the Pacific Ocean and the Rocky Mountains. It has a diverse geography, with rugged landscapes that include rocky coastlines, sandy beaches, for ...
,
Canada Canada is a country in North America. Its Provinces and territories of Canada, ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, covering over , making it the world ...
. In 2010, Sota Construction Services in
Pittsburgh Pittsburgh ( ) is a city in the Commonwealth (U.S. state), Commonwealth of Pennsylvania, United States, and the county seat of Allegheny County, Pennsylvania, Allegheny County. It is the most populous city in both Allegheny County and Wester ...
,
Pennsylvania Pennsylvania (; (Pennsylvania Dutch: )), officially the Commonwealth of Pennsylvania, is a state spanning the Mid-Atlantic, Northeastern, Appalachian, and Great Lakes regions of the United States. It borders Delaware to its southeast, ...
,
United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territo ...
, completed construction on its new 7,500 square foot corporate headquarters, which featured exterior cob walls along with other energy saving features like
radiant heat Thermal radiation is electromagnetic radiation generated by the thermal motion of particles in matter. Thermal radiation is generated when heat from the movement of charges in the material (electrons and protons in common forms of matter) i ...
flooring, a rooftop
solar panel A solar cell panel, solar electric panel, photo-voltaic (PV) module, PV panel or solar panel is an assembly of photovoltaic solar cells mounted in a (usually rectangular) frame, and a neatly organised collection of PV panels is called a pho ...
array, and
daylighting Daylighting is the practice of placing windows, skylights, other openings, and reflective surfaces so that sunlight (direct or indirect) can provide effective internal lighting. Particular attention is given to daylighting while designing a bu ...
. The cob walls, in conjunction with the other sustainable features, enabled the edifice to earn a
LEED Leadership in Energy and Environmental Design (LEED) is a green building certification program used worldwide. Developed by the non-profit U.S. Green Building Council (USGBC), it includes a set of rating systems for the design, constructio ...
Platinum rating in 2012, and it also received one of the highest scores by percentage of total points earned in any LEED category. In 2007, Ann and Gord Baird began constructing a two-storey cob house in Victoria,
British Columbia British Columbia (commonly abbreviated as BC) is the westernmost province of Canada, situated between the Pacific Ocean and the Rocky Mountains. It has a diverse geography, with rugged landscapes that include rocky coastlines, sandy beaches, for ...
,
Canada Canada is a country in North America. Its Provinces and territories of Canada, ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, covering over , making it the world ...
, for an estimated $210,000 CDN. The home of 2,150 square feet includes heated floors, solar panels, and a southern exposure to enable
passive solar heating In passive solar building design, windows, walls, and floors are made to collect, store, reflect, and distribute solar energy, in the form of heat in the winter and reject solar heat in the summer. This is called passive solar design because, unli ...
. Welsh architect Ianto Evans and researcher Linda Smiley refined the construction technique known as "Oregon Cob" in the 1980s and 1990s. Oregon Cob integrates the variation of wall layup technique which uses loaves of mud mixed with sand and straw with a rounded architectural stylism. They are experimenting with a mixture of cob and straw bale denominated " balecob".


Cob building code

In 2019 an appendix for the International Residential Code (IRC) was approved by a vote in the public comment hearings.Cob code appendix approved for the 2021 IRC
/ref> Appendix U of the IRC governs use of cob in load-bearing walls of single story residential structures. Based on currently available test data, the appendix limits the conditions under which cob may be used without engineering approval, such as seismic activity.


See also

* * * , a German Research-Institute for Cob-buildings * (a variant of cob used in southern Romania) * * * * * , the earliest human-made composite materials were straw, combined with mud, to make bricks and walls. * * * * * * * * * , a typical Devon cob building


References


Further reading

* ''Building With Cob, A Step by Step Guide'' by Adam Weismann and Katy Bryce. Published by Green Books ; 2006, . * ''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), . * ''The Cob Builders Handbook: You Can Hand-Sculpt Your Own Home'' by Becky Bee, Groundworks, 1997


External links


The Cob Builders Handbook

How to Build a Traditional Cob Oven
{{DEFAULTSORT:Cob (Material) Sustainable building Appropriate technology Natural materials Rammed earth Soil-based building materials Sustainable products Clay