Cob,cobb,orclom(in Wales) is a naturalbuilding materialmade fromsubsoil,water, fibrousorganic material(typicallystraw), and sometimeslime.[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 andsustainabilitymovements.
In technical building and engineering documents, such as theUniform Building Codeof 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 betweenpost and beamconstruction.
History and usage
edit
Cobis 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 ofcobandcobbingis unclear, but in several senses means tobeatorstrike,[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 asadobe,[5]lump clay,[5]puddledclay,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), andcat and clay.[8]
Cob structures can be found in a variety of climates across the globe. European examples include:
- in England, notably in the counties ofDevonandCornwallin theWest Country,and inEast Anglia(where it is referred to asclay lump)[9]
- in Wales, notably in ruralAnglesey[10]
- inDonegal BayinUlsterand in Munster, South-WestIreland[citation needed]
- inFinisterreand Ille-et-Vilaine inBrittany,where many homes have survived over 500 years and are still inhabited[citation needed]
Some of the oldest human-made structures in Afghanistan are composed oframmed earthand cob.[11]Cobwork (tabya) was used in theMaghrebandal-Andalusin the 11th and 12th centuries, and was described in detail byIbn Khaldunin the 14th century.[12]
Many old cob buildings can be found inAfrica,the Middle East, and the southwestern United States like theTaos Pueblo.[citation needed]A number of cob cottages survive from mid-19th-century New Zealand.[13]
Traditionally, English cob was made by mi xing the clay-based subsoil with sand, straw and water usingoxento trample it. English soils contain varying amounts ofchalk,and cob made with significant amounts of chalk are calledchalk coborwychert.The earthen mixture was then ladled onto a stonefoundationincoursesand trodden onto the wall by workers in a process known ascobbing.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 excellentthermal masswhich 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 isfireproof,[16]: 28 while "fire cob" (cob without straw or fiber) is arefractory 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
edit
When Kevin McCabe constructed a two-story, four bedroom cob house inEngland,UKin 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 atractorto mix the cob and adding sand or shillet, a gravel of crushedshale,to reduce shrinkage.[citation needed]
From 2002 to 2004, sustainability enthusiastRob Hopkinsinitiated the construction of a cob house for his family, the first new one inIrelandin circa one hundred years. It was a community project, but an unidentifiedarsonistdestroyed it shortly before completion.[18]The house, located at The Hollies Centre for Practical Sustainability inCounty 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 inWorcestershire,England,UK,designed byAssociated Architects,was sold for £999,000. Cobtun House was erected in 2001 and won theRoyal 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 theUnited Statesthere 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 SouthernGulf IslandsofBritish Columbia,Canada.[citation needed]
In 2010, Sota Construction Services inPittsburgh,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 likeradiant heatflooring, a rooftopsolar panelarray, anddaylighting.The cob walls, in conjunction with the other sustainable features, enabled the edifice to earn aLEEDPlatinum 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 inVictoria,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 enablepassive solar heating.[22]
Welsh architectIanto Evansand 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
editIn 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
edit- Adobe– Building material of earth and organic materials
- Appropriate technology– Concept in the philosophy and politics of technology
- ARGE-SH,a German Research-Institute for Cob-buildings
- Chirpici– Earth blocks for construction(a variant of cob used in southern Romania)
- Composite material– Material made from a combination of two or more unlike substances, the earliest human-made composite materials were straw, combined with mud, to make bricks and walls.
- Compressed earth block– Building material
- Earth structure– Building or other structure made largely from soil
- Earthbag construction– Building method
- LOHAS– Demographic defining a particular market segment
- Mudbrick– Earth blocks for construction
- Rammed earth– Construction material of damp subsoil
- Rice-hull bagwall construction
- Sod– Upper layer of soil and grass
- Sod house– Turf house used in early colonial North America
- Straw-bale construction– Building method that uses bales of straw
- Superadobe– Form of earthbag construction
- Vernacular architecture– Architecture based on local needs, materials, traditions
- Woodway House– Historic house in Devon, England, a typical Devon cob building
References
edit- ^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.
- ^Goodnow, Cecelia (October 5, 2007)."Thinking of building a cob home?".Seattle Post-Intelligencer.
- ^"cob, n2. 1."Oxford English Dictionary2nd. ed. 2009. CD-rom.
- ^"cob".Collins English Dictionary.HarperCollins.Retrieved13 January2017.
verb:(transitive) British informalto beat, esp on the buttocks
- ^abcdeRapp, George Robert. "Unbaked clay or mud",Archaeomineralogy.2nd ed. Berlin: Springer, 2009. Print.
- ^Oliver, Paul; Hess, Janet B. (23 February 2012)."African architecture".Encyclopædia Britannica.Retrieved13 January2017.
- ^abcEdwards, Jay Dearborn, and Nicolas Verton. "mud with straw",A Creole Lexicon Architecture, Landscape, People.Baton Rouge: Louisiana State UP, 2004. Print.
- ^"cat and clay" Websters Online Dictionary accessed March 23, 2015.
- ^Bouwens, Dirk."Earth Buildings and Their Repair".buildingconservation.Cathedral Publications Ltd.Retrieved13 January2017.[reproduced from The Building Conservation Directory, 1997]
- ^Hilling, John B. (2018).The Architecture of Wales From the First to the Twenty-First Century.University of Wales Press. p. 13.ISBN9781786832856.
- ^McArdle, Patricia (June 19, 2011)."Afghanistan's Last Locavores".The New York Times.
- ^Routledge Hill, Donald(1996). "Engineering". In Rashed, Roshdi; Morelon, Régis (eds.).Encyclopedia of the history of Arabic science.Vol. 3. p. 766.ISBN0-415-02063-8.
- ^Dozens of cob cottages arelisted on the Registerof 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.Retrieved21 August2013.
- ^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–.ISBN978-1-60059-534-9.Retrieved1 June2013.
- ^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 fromthe original(PDF)on 10 January 2015.Retrieved24 January2013.
- ^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.ProQuest1856858074– via ProQuest.
- ^Saxton, R. H. (1995)."The performance of cob as a building material".The Structural Engineer.73(7).The Institution of Structural Engineers:111–15.
- ^Practical Sustainability: About
- ^Welcome to The Hollies (2010-08-03)."The Hollies".thehollies.ie.Retrieved2010-12-04.
- ^"Sota Construction Services, Inc. - Sota Construction Corporate Offices".Archived fromthe originalon 2013-10-17.Retrieved2013-11-28.
- ^"Sota Construction Office Expansion | U.S. Green Building Council".
- ^Barton, Adriana (3 August 2007)."A Dream Home Made of Mud".The Globe and Mail.Retrieved2008-09-26.
- ^The History of Cob
- ^Building with Oregon Cob
- ^Cob code appendix approved for the 2021 IRC
Further reading
edit- Building With Cob, A Step by Step Guideby Adam Weismann and Katy Bryce. Published by Green Books; 2006,ISBN1-903998-72-7.
- 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),ISBN1-890132-34-9.
- The Cob Builders Handbook: You Can Hand-Sculpt Your Own Homeby Becky Bee, Groundworks, 1997ISBN978-0-9659082-0-7
- Essential Cob Construction: A Guide to Design, Engineering, and Buildingby Anthony Dente PE, Michael Smith, and Massey Burke, New Publishers Society; 2024, ISBN 978-0865719682.
External links
edit