Cob (material)

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Building a wall out of cob Cob wall mud construction.jpg
Building a wall out of cob

Cob, cobb, or clom (in Wales) is a natural building material made from subsoil, water, fibrous organic material (typically straw), and sometimes lime. [1] 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, termite proof, resistant to seismic activity, [2] 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 movements.

Contents

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 stitch" repair on old traditional cob cottage in Devon, England Cob stitch copy.jpg
"Cob stitch" repair on old traditional cob cottage in Devon, England
Maison de Jeanne, Severac-le-Chateau. Timber and cob construction Maison de Jeanne, Severac-le-Chateau.jpg
Maison de Jeanne, Sévérac-le-Château. Timber and cob construction

Cob is an English term attested to around the year 1600 [3] for an ancient building material that has been used for building since prehistoric times. The use of this material in Iran is more than 4000 years old. The etymology of cob and cobbing is unclear, but in several senses means to beat or strike, [4] which is how cob material is applied to a wall.

Many similar materials and methods of earthen building are used around the world, such as adobe , [5] lump clay, [5] puddled clay, chalk mud, [5] wychert , [5] clay daubins, [5] swish (Asante Twi), [6] torchis (French), [7] bauge (French), [7] bousille (French mud with moss), [7] beaten clay-pahsa (Central Asia), and cat and clay. [8]

Cob structures can be found in a variety of climates across the globe. European examples include:

Some of the oldest human-made structures in Afghanistan are composed of rammed earth and cob. [11] Cobwork (tabya) was used in the Maghreb and al-Andalus in the 11th and 12th centuries, and was described in detail by Ibn Khaldun in the 14th century. [12]

Many old cob buildings can be found in Africa, the Middle East, and the southwestern United States like the Taos Pueblo.[ citation needed ] A number of cob cottages survive from mid-19th-century New Zealand. [13]

Traditionally, English cob was made by mixing the clay-based subsoil with sand, straw and water using oxen to trample it. English soils contain varying amounts of chalk, and cob made with significant amounts of chalk are called chalk cob or wychert . 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 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. [14]

The walls of a cob house are generally about 24 inches (61 cm) 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. [15] The material has a long life-span even in rainy or humid climates, provided a tall foundation and large roof overhang are present

Cob is fireproof, [16] :28 while "fire cob" (cob without straw or fiber) is a refractory material (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. [17] :114

Modern cob buildings

An example of a modern cob building in the Pacific Northwest style. The exterior cob wall is limewashed for an attractive, uniform appearance. Home at Hollyhock.jpg
An example of a modern cob building in the Pacific Northwest style. The exterior cob wall is limewashed for an attractive, uniform appearance.
The Sota Construction Services Corporate Headquarters in Pittsburgh, Pennsylvania, United States, constructed of cob walls Sota Construction Office Building.jpg
The Sota Construction Services Corporate Headquarters in Pittsburgh, Pennsylvania, United States, constructed of cob walls
Decorating a cob oven Beautifying cob oven.jpg
Decorating a cob oven

When Kevin McCabe constructed a two-story, four bedroom cob house in England, 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 to mix the cob and adding sand or shillet, a gravel of crushed shale, to reduce shrinkage.[ citation needed ]

A modern cob house near Ottery St Mary, United Kingdom The Cob House - Cadhay.jpg
A modern cob house near Ottery St Mary, United Kingdom

From 2002 to 2004, sustainability enthusiast Rob Hopkins initiated the construction of a cob house for his family, the first new one in Ireland in circa one hundred years. It was a community project, but an unidentified arsonist destroyed it shortly before completion. [18] The house, located at The Hollies Centre for Practical Sustainability in County Cork, 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. [19]

In 2000-01, a modern, four bedroom cob house in Worcestershire, England, UK, designed by Associated Architects, was sold for £999,000. Cobtun House was erected 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 (yard) thick outer cob wall cost only £20,000.[ citation needed ]

In the Pacific Northwest of the United States 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 of British Columbia, Canada.[ citation needed ]

In 2010, Sota Construction Services in Pittsburgh, Pennsylvania, United States, completed construction on its new 7,500 square foot corporate headquarters, [20] which featured exterior cob walls along with other energy saving features like radiant heat flooring, a rooftop solar panel array, and daylighting. The cob walls, in conjunction with the other sustainable features, enabled the edifice to earn a LEED Platinum rating in 2012, and it also received one of the highest scores by percentage of total points earned in any LEED category. [21]

In 2007, Ann and Gord Baird began constructing a two-storey cob house in Victoria, British Columbia, Canada, 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. [22]

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. [23] [24] 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. [25] 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

Related Research Articles

<span class="mw-page-title-main">Adobe</span> Building material of earth and organic materials

Adobe is a building material made from earth and organic materials. Adobe 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 earthen construction, or various architectural styles like Pueblo Revival or Territorial Revival. Most adobe buildings are similar in appearance to cob and rammed earth buildings. Adobe is among the earliest building materials, and is used throughout the world.

<span class="mw-page-title-main">Straw</span> Agricultural byproduct of cereal crops

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 by weight of cereal crops such as barley, oats, rice, rye and wheat. It has a number of different uses, including fuel, livestock bedding and fodder, thatching and basket making.

<span class="mw-page-title-main">Mudbrick</span> Earth blocks for construction

Mudbrick or mud-brick, also known as unfired brick, is an air-dried brick, made of a mixture of mud mixed with a binding material such as rice husks or straw. Mudbricks are known from 9000 BCE.

<span class="mw-page-title-main">Mud</span> Mixture of water and any combination of soil, silt, sand, and clay

Mud is loam, silt or clay mixed with water. It is usually formed after rainfall or near water sources. Ancient mud deposits hardened over geological time to form sedimentary rock such as shale or mudstone. When geological deposits of mud are formed in estuaries, the resultant layers are termed bay muds. Mud has also been used for centuries as a construction resource for mostly houses and also used as a binder.

<span class="mw-page-title-main">Building material</span> Material which is used for construction purposes

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 and other structures, like bridges. Apart from naturally occurring materials, many man-made products are in use, some more and some less synthetic. The manufacturing of building materials is an established industry in many countries and the use of these materials is typically segmented into specific specialty trades, such as carpentry, insulation, plumbing, and roofing work. They provide the make-up of habitats and structures including homes.

<span class="mw-page-title-main">Rammed earth</span> Construction material of damp subsoil

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.

<span class="mw-page-title-main">Cordwood construction</span> Wall construction from pieces of wood bonded with mortar or clay

Cordwood construction is a term used for a natural building method in which short logs are piled crosswise to build a wall, using mortar or cob to permanently secure them. This technique can use local materials at minimal cost.

Earthbag construction is an inexpensive building method using mostly local soil to create structures which are both strong and can be quickly built.

<span class="mw-page-title-main">Loam</span> Soil composed of similar proportions of sand and silt, and somewhat less clay

Loam is soil composed mostly of sand, silt, and a smaller amount of clay. By weight, its mineral composition is about 40–40–20% concentration of sand–silt–clay, respectively. These proportions can vary to a degree, however, and result in different types of loam soils: sandy loam, silty loam, clay loam, sandy clay loam, silty clay loam, and loam.

<span class="mw-page-title-main">Natural building</span> Sustainable construction practice

Natural building is the construction of buildings using systems and materials that emphasize sustainability. This in turn implies durability and the use of minimally processed, plentiful or renewable resources, as well as those that, while recycled or salvaged, produce healthy living environments and maintain indoor air quality. Natural building tends to rely on human labor, more than technology. As Michael G. Smith observes, it depends on "local ecology, geology and climate; on the character of the particular building site, and on the needs and personalities of the builders and users."

<span class="mw-page-title-main">Wychert</span> Building material of chalk, clay, and straw

Wychert or witchert 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. This historic method of building construction is mainly localised to Haddenham and the surrounding local area in Buckinghamshire. Also found, amongst others, as a similar 'slow process' construction is a thatched example of 'mud wall' surrounding two sides of the churchyard at St. Luke's Church, Laughton, Leicestershire. One of the largest known wychert structures is Haddenham Methodist Church.

<span class="mw-page-title-main">Earth structure</span> Building or other structure made largely from soil

An earth structure is a building or other structure made largely from soil. Since soil is a widely available material, it has been used in construction since prehistory. It may be combined with other materials, compressed and/or baked to add strength.

<span class="mw-page-title-main">Compressed earth block</span> Building material

A compressed earth block (CEB), also known as a pressed earth block or a compressed soil block, is a building material made primarily from an appropriate mix of fairly dry inorganic subsoil, non-expansive clay, sand, and aggregate. Forming compressed earth blocks requires dampening, mechanically pressing at high pressure, and then drying the resulting material. If the blocks are stabilized with a chemical binder such as Portland cement they are called compressed stabilized earth block (CSEB) or stabilized earth block (SEB). Typically, around 3,000 psi (21 MPa) of pressure is applied in compression, and the original material volume is reduced by about half.

<span class="mw-page-title-main">Superadobe</span> Form of earthbag construction

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 employ corbelled arches, corbelled domes, and vaults to create sturdy single and double-curved shells. It has received growing interest for the past two decades in the natural building and sustainability movements.

Ceramic houses are buildings made of an earth mixture which is high in clay, and fired to become ceramic. The process of building and firing such houses was developed by Iranian architect Nader Khalili in the late 1970s; he named it Geltaftan. "Gel" means "clay" and "taftan" means "firing, baking, and weaving clay" in Persian language. Khalili's research into creating ceramic houses was strongly based on the idea that permanent, water-resistant, and earthquake-resistant houses could be built with the implementation of the four elements: earth and water to build the forms, and fire and air to finish them. His impassioned work led to a few small scale projects in Iran, including the Javadabad Elementary School, and the Ghaled Mofid restoration project. Aside from Khalili's own documented work, there seems to be little widespread research on ceramic houses.

<span class="mw-page-title-main">Light clay</span>

Light clay is a natural building material used to infill between a wooden frame in a timber framed building using a combination of clay and straw, woodchips or some other lighter material.

Alternative natural materials are natural materials like rock or adobe that are not as commonly used as materials such as wood or iron. Alternative natural materials have many practical uses in areas such as sustainable architecture and engineering. The main purpose of using such materials is to minimize the negative effects that built environments can have on the planet, while increasing the efficiency and adaptability of the structures.

<span class="mw-page-title-main">Wattle and daub</span> Building technique using woven wooden supports packed with clay or mud

Wattle and daub is a composite building method used for making walls and buildings, in which a woven lattice of wooden strips called "wattle" is "daubed" with a sticky material usually made of some combination of wet soil, clay, sand, animal dung and straw. Wattle and daub has been used for at least 6,000 years and is still an important construction method in many parts of the world. Many historic buildings include wattle and daub construction.

<span class="mw-page-title-main">Musgum mud hut</span>

Musgum mud huts or Musgum dwelling units are traditional domestic structures built of mud by the ethnic Musgum people in the Maga sub-division, Mayo-Danay division, Far North Province in Cameroon. Referred to in Munjuk as Tolek, the dwellings are built in a variety of shapes, such as tall domed or conical dwellings or huts, some with a reverse-V shape, and others with geometric designs.

Ianto Evans is a Welsh-American applied ecologist, landscape architect, inventor, writer, social critic, and teacher. He is known for his work building, writing and teaching about natural building, cob and high-efficiency solid-fuel stoves, ovens and heaters.

References

  1. Wright, Joseph. "COB(B, sb3. 1.", The English Dialect Dictionary, Being the Complete Vocabulary of All Dialect Words Still in Use, or Known to Have Been in Use during the Last Two Hundred Years. London: H. Frowde;, 1898. 676-677. Print.
  2. Goodnow, Cecelia (October 5, 2007). "Thinking of building a cob home?". Seattle Post-Intelligencer.
  3. "cob, n2. 1." Oxford English Dictionary 2nd. ed. 2009. CD-rom.
  4. "cob". Collins English Dictionary. HarperCollins. Retrieved 13 January 2017. verb: (transitive) British informal to beat, esp on the buttocks
  5. 1 2 3 4 5 Rapp, George Robert. "Unbaked clay or mud", Archaeomineralogy. 2nd ed. Berlin: Springer, 2009. Print.
  6. Oliver, Paul; Hess, Janet B. (23 February 2012). "African architecture". Encyclopædia Britannica. Retrieved 13 January 2017.
  7. 1 2 3 Edwards, Jay Dearborn, and Nicolas Verton. "mud with straw", A Creole Lexicon Architecture, Landscape, People. Baton Rouge: Louisiana State UP, 2004. Print.
  8. "cat and clay" Websters Online Dictionary accessed March 23, 2015.
  9. Bouwens, Dirk. "Earth Buildings and Their Repair". buildingconservation.com. Cathedral Publications Ltd. Retrieved 13 January 2017.[reproduced from The Building Conservation Directory, 1997]
  10. Hilling, John B. (2018). The Architecture of Wales From the First to the Twenty-First Century. University of Wales Press. p. 13. ISBN   9781786832856.
  11. McArdle, Patricia (June 19, 2011). "Afghanistan's Last Locavores". The New York Times .
  12. Routledge Hill, Donald (1996). "Engineering". In Rashed, Roshdi; Morelon, Régis (eds.). Encyclopedia of the history of Arabic science. Vol. 3. p. 766. ISBN   0-415-02063-8.
  13. Dozens of cob cottages are listed on the Register of the New Zealand Historic Places Trust, e.g. "Ferrymead Cob Cottage". Rarangi Taonga: the Register of Historic Places, Historic Areas, Wahi Tapu and Wahi Tapu Areas. New Zealand Historic Places Trust Pouhere Taonga. Retrieved 21 August 2013.
  14. Snell, Clarke; Callahan, Tim (2009). Building Green: A Complete How-to Guide to Alternative Building Methods : Earth Plaster, Straw Bale, Cordwood, Cob, Living Roofs. Sterling Publishing Company, Inc. pp. 276–. ISBN   978-1-60059-534-9 . Retrieved 1 June 2013.
  15. Goodhew, Steven; Griffiths, Richard (2005). "Sustainable earth walls to meet the building regulations" (PDF). Energy and Buildings. 37 (5). Elsevier: 1. Bibcode:2005EneBu..37..451G. doi:10.1016/j.enbuild.2004.08.005. Archived from the original (PDF) on 10 January 2015. Retrieved 24 January 2013.
  16. Cioruța, Bogdan (2016). "Trends In The Techniques Of Design And Building Traditional Earth Houses". Scientific Bulletin Series D: Mining, Mineral Processing, Non-Ferrous Metallurgy, Geology and Environmental Engineering. 30 (2). North University of Baia Mare: 21–31. ProQuest   1856858074 via ProQuest.
  17. Saxton, R. H. (1995). "The performance of cob as a building material". The Structural Engineer. 73 (7). The Institution of Structural Engineers: 111–15.
  18. Practical Sustainability: About
  19. Welcome to The Hollies (2010-08-03). "The Hollies". thehollies.ie. Retrieved 2010-12-04.
  20. "Sota Construction Services, Inc. - Sota Construction Corporate Offices". Archived from the original on 2013-10-17. Retrieved 2013-11-28.
  21. "Sota Construction Office Expansion | U.S. Green Building Council".
  22. Barton, Adriana (3 August 2007). "A Dream Home Made of Mud". The Globe and Mail . Retrieved 2008-09-26.
  23. The History of Cob
  24. Building with Oregon Cob
  25. Cob code appendix approved for the 2021 IRC

Further reading