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CRI's Cob Code Proposal

Approved for the 2021 International Residential Code

What is Cob?

Cob is an ancient method of building with earth. Clay-rich soil is mixed with water, straw, and often sand to a dough-like consistency and sculpted into walls while still wet. Under different names, the technique has been common for centuries throughout northern Europe and in parts of Asia, Africa, and the Americas. There are more than 20,000 cob homes in the English county of Devon alone, some of which are as much as 600 years old and still inhabited today.

The Cob Revival

In recent decades cob has enjoyed a revival in North America, Britain, and elsewhere. The resurgence of interest is driven in part by the fact that cob is one of the most ecologically sensible ways to build a house. The materials are often available for low cost or free on or close to the building site. Cob can easily be sculpted into whimsical and curvilinear shapes, making each cob building a unique work of art. Cob walls are highly fire-resistant and contain no harmful chemicals. Despite these advantages, there have been many obstacles to building with cob legally, including an almost total absence of building codes.

Developing the Code

The Cob Research Institute is a 501(c)3 non-profit organization founded in 2008. Our mission is to remove legal obstacles to building with cob while retaining its character as a simple, ecologically sound building system. After many years of intensive collaboration with several universities and testing facilities, as well as dozens of cob builders, engineers, architects, and code specialists, we have produced the world’s first complete model building code for cob. In 2019, our code was approved by voting members of the International Code Council as an appendix to the 2021 International Residential Code.

Next Steps

Despite this enormous victory, much work remains to be done. The code needs to be refined and improved through further laboratory testing and real-world application. A fire-resistance rating needs to be established. Better systems for insulating cob walls must be developed. A great deal of outreach to and education of both building officials and cob builders is required before the code can make its maximum potential impact on the health, safety, and sustainability of building practices at home and around the world. With increasing concerns about the fire safety of our built environment and the contribution of buildings to climate change, our work is more urgent than ever.

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