Partially covering a building with earth adds to the thermal mass of the structure. Combined with insulation, this results in both amplitude dampening and phase shifting. In other terms, earth sheltered structures receive both a degree of cooling in Summer and heating in Winter. This reduces need for other measures of heating and cooling, saving energy. A potential disadvantage of a thermally massive building in cooler climates is that after a prolonged period of cold, when the external temperature increases again, the structures internal temperature tends to lag behind and take longer to warm up (assuming no other form of heating).