Adobe, Cob, Soil-Cement & Rammed Earth - 4/4/2003 - Home Foundation Structure Framing

Adobe, Cob, Soil-Cement & Rammed Earth

Building with soil based materials

Homes made from soil based materials have been called various names; adobe and cob are terms often used to describe sun dried clay materials. Rammed earth and soil-cement brick refer to a popular method used today, with a cement additive and pressure to mold the blocks or bricks.

Earth building techniques are practiced in many parts of the world. While most people might associate this construction practice with third world countries, there are earth building standards in China, Peru, Turkey, New Zealand and Australia. A renewed interest in green building materials has also kept the technique visible in the United States, mostly in the southwestern area of the country.

Public perception may not accept earthen buildings in some regions more familiar with wood framed or masonry homes. Lending, insurance and code requirements may also provide barriers.

Adobe and rammed earth construction are an insignificant percentage of the residential construction market. Experienced labor may be unavailable for this specialized technique in some areas of the country.

	Because the major material component is derived from the site, building material costs are lower.
	Thick earth material walls provide good sound deadening and thermal mass properties.
	Building with renewable earth materials.

Because the major material component is derived from the site, building material costs are lower than traditional techniques. However, the method is labor intensive and may require special equipment and craftsman. Installed costs can be at $80/sf of wall or more, depending on labor cost and purchase or rental equipment.

Thick earth material walls provide good thermal mass properties, which should lower operational costs

The International Residential Code does not address rammed earth and adobe structures. Some local jurisdictions may allow the technique or allow the procedure with engineering approval. An example is New Mexico at http://www.nmcpr.state.nm.us/nmac/parts/title14/14.007.0004.htm.

Not Applicable

A strong foundation is particularly important with this type of construction because of the immense weight of the wall material. Each square foot of wall material might weight 100 or more pounds; therefore, each linear foot of 8' high wall could weigh more than 800 pounds. Rock substrate, stone and concrete are popular foundation materials used to support earth material walls. Older methods of this type of construction were as simple as forming the walls by hand. The walls could be built in lifts, so that the lower portions of the wall could cure before supporting the weight of the wall above. The mixture could also be formed into blocks and then sun dried before assembly. Rammed Earth and TerraBrick systems compact a soil-cement mixture. Cement is added to the soil, and hydraulics or pneumatics apply a force to shape and bond the materials together. The load bearing strength of the resulting blocks can vary depending on the type of soil and amount of cement used, but testing has shown that this method can produce blocks with a 900 to 2,240 psi compressive strength.

Not Applicable

Thick earth material walls provide good sound deadening and thermal mass properties.