A form of earth-sheltered house that has been receiving much attention is referred to as an “Earthship.” These houses are built to be self-contained and independent; their design allows occupants to grow food inside and to maintain their own water and solar electrical systems. Some builders believe they have proven the design’s ability to tap into the constant temperature of the earth and store additional energy from the sun in winter, although a back-up system, usually electric, may be recommended.
These Earthships carry out their environmentally conscious theme by employing unusual building materials in the form of recycled automobile tires filled with compacted earth for thermal mass and structure. Aluminum or tin cans are also used for filling minor walls that are not load-bearing. Foam insulation can be applied to exposed exterior or interior walls and covered with stucco. Interior walls can also be drywalled for a more conventional look.
There has been a recent surge in homes that use soil as a primary building material. This type of construction is literally “old as the hills.” Some ancient reinforced at the site, architecture, such as the Great Wall of China, shows the durability of earthen construction. So building with earth and sand, always plentiful and inexpensive, is not a new idea.
Although these houses do not typify the earth-sheltered construction designs discussed in this publication, earth is a major component in their construction material and many of the same energy efficient ideas are used. Many buildings in the south-western United States use adobe—bricks constructed of tightly compacted earth, clay, and straw—as their main construction material.
Another building material is “rammed earth.” This process entails mixing earth and cement, and packing it into the wall forms with a pneumatic tamper. The result is a rough approximation of sedimentary floors, walls, and rock. In fact, this “stabilized earth” achieves compressive strengths estimated to be about half that of concrete. Walls can be made even thicker with little added cost, since the labor and the formwork are the more costly items of a wall. Although a steel-reinforced, eight-inch (20.32 centimeters) thick earthen-wall is strong enough for load-bearing walls, extra mass, coupled with good solar design, can offer better insulation and increased heating and cooling capacity. Compared to earth-sheltered houses, additional insulation may not be necessary in rammed-earth houses, depending on the area’s climate.