Cob Building

After reading for years about Native American and Mexican adobe houses and the construction of the Egyptian Pyramids, I realized that these were both examples of cob building. Checking at the time with historical records, modern investigative research, and personal contacts in both Egypt (archaeology) and in New Mexico, this was confirmed in certain ares of each locale. The same materials were used and are still used in parts of NM; sometimes bricks/blocks were formed, and adobe has been molded and still is among small Native American communities or pueblos.

Only after this did I find many examples of cob building in England - and then in the United States by green businesses set up to build these structures, and by eco-friendly individuals on their own. Several have written books that you might check out of the library or find at your local book store or green building supply outlet.

Building Green: A Complete How-To Guide to Alternative Building Methods Earth Plaster * Straw Bale * Cordwood * Cob * Living Roofs by Clarke Snell and Tom Callhan is excellent. This book provides step-by-step instructions and dozens of correlated pictures.

More recently, I have looked at the marerials of several house plans for cob building and examining the printed materials used in construction of a cob house in Knox County, Ohio. I've come up with some foundational information about arches and, while what I have discovered may not fully meet your needs, I have supplied information for additional specific places to go for help. I've also supplied several links to cob building sites that will anwser email questions about cob related projects, and a couple of descriptions of some very good books that illustrate methods and give instructions in cob building.

It appears that the sturdy construction of cob, especially if straw is added into the mix of clay and sand, can support an arch over an arched window that is otherwise standard window size or even double the width of a standard window in today's construction of houses. In several pictures of completed cob homes, arches across dooorways that span twice the width of standard house dooralso appeared strong.

You can set the window or door temporarily in place, and pretty simply mold the cob around it and let dry.

Several sets of plans and intructions I read suggested that the arch should be made more narrow in the center than on the ends, so that the weight the arch must bear can be somewhat reduced. No specific measurements were given.

None of the house plans indicated any means for determining the lengths of arches of any longer possible spans than a standard window, double window, door width, or double door width. However, since the cob-with-straw-mix is extremely strong when sun-baked, a longer arch span of this material may be possible. Based in standard engineering calculations, the base supporting the arch would need to be of a size, height, strength, and shape adequate to support the span of cob.

For longer cob arches, suspension bridge building engineering formulas would likely work, and your local university engineering and architecture departments would probably help you with these at no charge. Graduate students often do these sorts of projects and department professors check their work. A link on building suspension bridges is at the following:

Building a Suspension Bridge

Cob revivalist Ianto Evans gave a series of Cob Workshops at the Ohio State University in 2004. Evans helped attendees to refresh current skills and to learn new ones as well. One lesson taught was that a properly constructed and molded cob house can last for over 100 years.

History of Cob Building

Apprenticeship Program: Cob Cottage Company

•  Cob Projects - Timeless Art of Cob Building - hundreds of projects and fantastic photos.
• cobcottage site for The Cob Cottage Company features information and resources about building with cob.
• cobworkshops.org lists many workshops featuring cob in North America.
• naturalhomes.org lists workshops from around the world related to cob.
• earthedworld.co.uk a fine, informative site about cob, listing workshops, forums, and an extensive photo gallery.
• cobworks.com information, photos, workshops related to cob.
• coblist email discussion group about cob.
• daycreek.com page of photos and description of cob.
• spiralworks.com is devoted to sustainable community development, and specializes in teaching about cob on the East Coast.
• housealive.org This site is mostly focused on cob, and offers information and workshops.
• barefootbuilder.com has information about cob and sponsors cob workshops in Tennessee
• mudgirls.ca A women's cobbing cooperative in Canada that offers workshops, etc.
• edwardsecobuilding.com features information about cobbing, with photos, articles, courses, links, etc. in the UK.
• cobbuildersforum.com - Forum specific to cob building; gallery, videos, and workshops listed.