Foundations

Foundations

The foundation is one of the most critical parts of any building. The best foundation for an Earth Block building is made of steel reinforced concrete. Earth Blocks, or adobes, even if stabilized (made from soil mixed with cement), are NOT to be used for foundations, as earthen blocks are susceptible to severe damage in the face of long-term moisture exposure. Foundations typically consist of two major components - footings and stem walls.

Footings are the first major component of the foundation.

"Footings should be at least eight inches thick and not less than two inches wider in each side than the foundation stem walls above. All foundation walls which support adobe units shall extend to an elevation not less than eight inches above then finished grade."

(Section 2413(m) of the Adobe Code-City of Mesa, Maricopa County, State of Arizona)

Stem walls are the second major component of the foundation. Although codes vary, they extend vertically from the top of the footing to appoint six to twelve inches above the finished grade. As a general rule, the wetter the climate, the higher the stem wall should project above the finished grade. The interior finished floor should be at least four inches below the top of the stem wall. This results in a curb which keeps the first course of Earth Blocks from sustaining water damage in the event of minimal interior flooding. The stem wall must be at least as thick as the exterior earth Block wall above.

Both the footing and the stem wall should be reinforced with rebar. Again, the codes vary depending upon location, but at least two horizontal half-inch (#4) continuous rebar should be in the footing. It is important to prevent contact between rebar and the earth, therefore, the rebar should be at least three inches up from the bottom of the footing and at least two inches in from the sides. Likewise, the stem wall should have at least two horizontal half-inch (#4) continuous rebar near the top of the wall. Additional horizontal rebar and/or vertical rebar may be required, depending on the region.

In many areas, concrete trucks or pumpers are not available and concrete is mixed by hand on the ground. It is unlikely under these circumstances that the builder would be willing to fill a footing and stem wall trench with pure concrete due to the cost of labor and the cost of the Portland cement. In these situations, rocks are frequently used to fill the trench, With this scenario it is best to at least encase the rock fill in concrete and keep the rebar encased in concrete as well. It should be noted that concrete varies widely in quality. Factors such as the quality of the Portland cement itself, the amount of water added to the mixture, the amount of time the concrete has been mixed, and the skill of the workers involved all affect the quality of the finished product.

Another alternative foundation system, the rubble or gravel-filled foundation, was popularized by the famous architect Frank Lloyd Wright. With this system a trench is filled with gravel. The size of the gravel can vary, with the largest no more than three inches in diameter (three inch minus). This gravel-filled trench is filled with six-inch lifts, with each lift or layer being compacted pneumatically or by hand. A grade beam of continuous, steel reinforced concrete at least eight inches thick is then poured on top of the gravel-filled trench. The advantage of this system is the obvious savings in the quantity of concrete. There is also some speculation - and experimentation by the Chinese - that this system may be superior in seismic zones, however, more testing must be done before this theory can either be proved or disproved.

Flooring options depend upon the climate, region, material availability and client preference. Although not all flooring systems have structural ramifications, some do provide lateral support at the floor or ground level. Floors may be of wood, earth, concrete, or other material. If a concrete slab is used, it can be attached to a stem wall by virtue of rebar connections which can have some positive structural significance. When pouring a concrete slab for a floor, care should be taken to thicken the slab wherever an interior earthen wall will be located.

Earth Block, Inc.

P.O. Box 3605
Pagosa Springs, CO 81147
Jim or Nora Hallock
Phone: 970-883-2456
Email: earthblock@juno.com