What is a Cob Building?

A cob building is a structure which has been built with the use of cob, a building material made from a blend of sand, straw, and clay. Cob has been used in construction for thousands of years all over the world, with cob building being associated in particular with many areas of England and Ireland. This building material is similar to adobe, a material native to the Americas, and structures made from cob have endured hundreds of years of continuous use.

To make a cob building, people start out by creating a solid foundation. Framing is erected around the foundation, and packed with straw bales, sandbags, or other materials, depending on regional norms. Then, a cob mixture is used to plaster the structure, with people molding the cob by hand. One of the great features of cob is that it can be used to integrate sculptural elements into a structure, such as curved walls, ornamental sculpted devices, and so forth. The flexibility and durability of cob allows people to create truly unique and distinctive structures, as well as more sedate and ordinary ones which look like they would fit right in on an English country lane.

Once a structure has been thoroughly covered with cob, the cob is allowed to cure. Like adobe, the cob becomes hard and impermeable during the building process, which makes it suitable for a number of climates. The cob can be covered in plaster or left in a raw state, and architectural features like wooden window trim, floor tiles, and windows can be added in the process of finishing the structure. For cold climates, it may be necessary to use more insulation when building with cob, while warmer climates can require other building adaptations.

A revival in interest in cob building began in the late 20th century, when people became interested in traditional building techniques and sustainable building. Building with cob involves the use of natural, renewable resources which can often be found right on the building site, and it results in durable structures which tend to be very heat efficient, making them environmentally friendly.

People may enjoy working with cob because it allows them to construct an environmentally friendly structure, and because it allows them to be very involved in the construction of their homes. People can learn the basics in a weekend workshop, and a growing acceptance of natural building techniques has made resources like professional cob builders available in many communities. Constructing a cob building can require some challenging negotiations of building codes and community norms about what a building should look like, but it can also be very rewarding.