It is generally considered that earth-sheltered structures in this region are of marginal benefit to the operating energy costs of a building. It must be recognized that practically all earth sheltered homes are designed with passive solar principles. From the standpoint of the quality of the energy source, earth-sheltering and solar energy can be considered superior to fossil fuels. In areas of cold winter temperatures, insulation is added to the full exterior of a building that is earth-sheltered. This prevents temperature variations in the upper walls.
Extruded polystyrene is the most suitable insulation material for earth contact.
This insulation has CFC's or HCFC's. If the building is bermed, the upper portion of the building should be insulated to the same standards used in above ground structures. This is too shallow to effectively insulate the building and is the reason that roof insulation is required. The lack of air infiltration in an earth-sheltered structure intensifies the need to eliminate pollutants within the house. Mechanically-controlled air infiltration via energy recovery ventilators can mitigate such concerns and should be strongly considered, particularly those models with humidity regulation capabilities.