The construction materials for each type of structure will vary, depending on characteristics of the site, climate, soils, and design. However, general guidelines show that houses more deeply buried require stronger, more durable construction materials. Materials must provide a good surface for waterproofing and insulation to withstand the pressure and moisture of the surrounding ground. When soil is wet or frozen, the pressure on the walls and floors increases. Pressure also increases with depth, so materials such as concrete and reinforced masonry, wood, and steel are all suitable. To reduce your transportation costs, it helps if appropriate materials are locally available.
Concrete is the most common choice for constructing earth-sheltered buildings. Not only is it strong, it is also durable and fire resistant. Several forms of concrete are used Lightly reinforced concrete, which is poured and is used for noncritical structural elements such as concrete foundations, floor slabs, and exterior walls with less than 6 feet (1.83 meters) of earth cover. Precast reinforced concrete can resist loads at any reasonable depth and can be used for roofs. Concrete absorbs and stores heat, helping to prevent temperature swings that can damage some building material.
Precast concrete components are cured at a plant or on-site location before they are used, thereby decreasing construction time and cost in comparison to cast-in-place forms. The uses and advantages of precast and cast-in-place concrete are similar, except that precast concrete works best in simple or repeatable shapes. Special care must be taken to make the joints between sections watertight.
Concrete can also provide supplemental strength in other types of earthen construction. For example, a concrete topping can be added to wooden roof planks, and cement “parging” (or coating) can be added to walls with masonry construction before waterproofing.
Masonry (i.e., brick or stone) can be used for walls that will receive vertical or lateral pressure from earth cover. It is reinforced with steel bars that are put in the core of the masonry in places of high stress, such as weight-bearing walls or walls with earth against them. Masonry generally costs less than cast-in-place concrete.
Wood can be used extensively in earth-sheltered construction for both interior and structural work including floors, roofs, and exterior walls. Wood is attractive for its color and warmth, and complements tile and masonry, as well as concrete walls, floors, and ceilings. However, using wood as a structural material requires wooden frame walls, which must withstand lateral pressure, be restricted to a burial depth of one story. Beyond this depth, the rapidly increasing cost of wood construction restricts most builders from using it as a structural material. Although wood can cost less than other materials, it does not offer the strength that a material such as steel does, so it may not be the best choice for structural material in some houses. Wood must also be treated with preservatives to prevent damage from moisture. If your structure can make practical use of wood as a framing material, employing carpenters who can rapidly construct a timber frame for an earth-sheltered house can decrease labor costs.
Steel is used for beams, bar joists, columns, and concrete reinforcement. It is particularly useful because of its high tensional and compressional strength. The primary disadvantage of steel is that it must be protected against corrosion if it is exposed to the elements or to groundwater. It is also expensive, so it must be used efficiently to be economical as a structural material.