Cob is a composition of clay (sticky mud bonding), straw (cellulose), sand (aggregate) and water mixed together and formed into a lump (ball). Cob when made into a more fluid base can be poured into molds and baked in the sun forming bricks. Both cob styles have been used in building homes/dwellings for centuries across the globe. Materials are abundant and inexpensive and require human labor to produce/build.
Cob homes/buildings are strong enough to support roofs and multi story levels. Cob exterior walls are typically 15” to 24” thick and are ideal for passive thermal solar applications. In climates where insulation is needed it would be suggested to use an amendment such as vermiculite. Or incorporating some minor design and material changes to make a “hybrid” natural material utilizing straw bales for the north and west walls.
What makes Cob such a great natural material to build with? There are three primary reasons: FIRST, the materials are “organic” and do not require chemicals in order to build a home so it provides for a “healthy” environment. SECOND, cob utilizes clay soil which is “dirt cheap” and found everywhere. THIRD, requires inexpensive tools and minimal experience to build. It’s quite common to find 700 year old cob homes across England and France still being lived in.
All homes should provide for a healthy environment but Cob built homes are exceedingly healthy (chemical free from formaldehyde, volatile organic compounds -paints) and built without harmful, carcinogenic materials. Cobs built homes are unique, beautiful, warm and inviting. Inspiration is limited only to one’s individual creativity.
Cob homes are “GREEN and SUSTAINABLE”. “Stick built homes” require a lot of wood (lumber). The average American home needs approximately 27,000 board feet or 11-30 trees (size of tree determines how many) for a 1200 square foot home. In addition, the cost to mill and transport adds to the carbon footprint. Word on the street is in the very near future lumber length will be limited to only 16 feet due to increased demand for lumber….this will raise the cost to build a home.