Green Building Primer

Earth-sheltered design employs the earth as a major component of a building's thermal control system. A house that is surrounded (completely or partially) by earth that stays at a steady 55-60° temperature year round requires less heating in the winter and less cooling in the summer. For comparison, a house that is exposed to 20° winter air needs to be heated 50° to be a comfortable 70°, while a house exposed to 55° earth only needs to be heated 15° to reach that same comfortable 70°

Advantages of Earth Sheltered Design (in general):

• House is less susceptible to outside air temperatures, so temperatures inside house are more stable than in conventional homes, making rooms more comfortable. Energy needed to maintain a comfortable temperature is lower than in a conventional house.
• Less outside maintenance required as earth covers part or all of exterior.
• Natural soundproofing.
• Building blends into the landscape.
• Reduced insurance costs because extra protection from high winds, hailstorms, and natural disasters like tornados and hurricanes.
• Most cost effective in climates that have significant temperature extremes and low humidity e.g. Rocky Mountains and northern Great Plains, as earth temperatures vary much less than air temperatures, allowing earth to absorb extra heat from house in hot weather or to insulate house to maintain warmth in cold weather.

Disadvantages of Earth Sheltered Design:

• Initial costs of construction may be up to 20% higher
• Increased care required to avoid moisture problems during construction and after house is completed
• May be harder to resell, and it may complicate the mortgage application process
• Flat sites require extensive excavation
• Not all sites are suitable. Best soils are granular, as they compact well for bearing the weight of construction materials, and are permeable, allowing water to drain quickly. Poorest soils for earth-sheltered homes are cohesive soils like clay, which may expand when wet and have poor permeability
• Radon, produced naturally from the radioactive decay of uranium in rock, can reach dangerous levels when trapped, and thus radon levels must be considered when locating the home. There are methods to reduce radon buildup in earth-sheltered buildings
• The water table must be low enough to ensure that water will naturally drain away from the building, and to avoid water pressure against underground walls. Seasonal or regular surface water flows must be channeled away from the structure