How much earth cover does the average building need?
That depends on circumstances. In the Texas area we are experimenting with a 9-foot-thick earth cover, in the tentative belief that a 9-foot depth is about right for the temperature time lag experienced in one season and a nearly constant earth temperature of 65°F. Circulation of unconditioned outside air is expected to provide the major requirements for heating and cooling. The selection of the proper depth of cover, its composition, moisture content and type of cover (asphalt or vegetation) has a profound effect on heating and cooling requirements. In general, however, a depth can be determined which provides significant heat transfer delay and moderation.