by Steve Graham, Networx
Cob construction is like shaping a house with artists’ clay but never baking it. Cob (which borrows an Old English word for mound and has nothing to do with corn) is a mass of straw, clay, sand, and water. In a gradually reviving form of construction, it is hand-sculpted into buildings while the mixture is still wet.
Cob construction may be the world’s most environmentally friendly building process. There are no additives or chemicals. No energy is consumed in heating or forming the material, and no heavy machinery is required. In the right areas, the basic building materials all can be obtained locally.
Cob was used for many years in Europe, and is still widely used in Africa. Many European earth structures are still standing despite centuries of rain and harsh winters.
It is closely related to adobe, a popular building style in the Southwestern United States. The main difference is bricks. Adobe uses sun-dried earth bricks connected with mud mortar. Cob construction is a simpler concept, but takes detailed planning. Here are the first steps of cob construction.
Choosing a Site
The most important factor is drainage. Cob will break down if it is submerged. Make sure that even a 1,000-year flood won’t saturate your cob walls.
Instead, build on a hill to ensure good drainage. Cob works well on sloped properties that complicate standard frame construction. Also look for full sun exposure in the winter, and land with available clay soils, if possible.
Designing the House
Spend plenty of time designing every inch and each curve of a cob house. Make a scale model of the house, including surrounding trees and landscape features. Without four-foot sheets of drywall and other pre-measured supplies to confine the project, much of the house can be as creative as your imagination.
Thoroughly consider lighting and insulation. Take advantage of natural solar light and heat, and design thick walls with embedded straw-bale insulation where needed. After creating a design and consulting with cob experts, obtain the proper building permits (even though very few municipal housing codes explicitly cover cob construction).
You can’t just buy cob mix at a home improvement store, but you may be able to creatively find the materials for free or really cheap. All but the richest agricultural soil and rockiest mountain landscapes have some mix of sand and clay. If either material is not immediately available, look for road projects or construction sites where they may be looking to get rid of clay and sand. Farmers often sell cheap straw bales. As long as the straw is not rain-rotted, it should hold the sand and clay together nicely. With materials in hand and a model of the house, you’re ready to build.
Cob construction is an old, simple and environmentally friendly building technique that is new to most of us. For cob building workshops and classes, and other information, visit the Cob Cottage Company. “The Hand-Sculpted House” by Ianto Evans, Michael Smith and Linda Smiley, is a detailed cob construction handbook that provided background information for this article.