Earth sheltering is the architectural practice of using earth for external thermal mass against building walls. This is a passive solar practice.
The principle is that the earth, because of its high density, undergoes slow temperature changes and thus presents a fairly constant exterior temperature at the wall. In most of the United States, the average temperature of the earth once well below the frost line is around 55 to 57 degrees Fahrenheit (13 to 15 degrees Celsius). Thus, at the base of a deep earth berm, the house is heated against an exterior temperature gradient of perhaps ten to fifteen degrees, instead of against a steeper temperature grade where air is on the outside of the wall instead of earth. In the summer, the temperature gradient actually helps to cool the house.
Earth sheltering may take one of several forms:
- Earth berming: Earth is piled up against exterior walls and packed, sloping down away from the house
- In-hill construction: The house is set into a south-facing slope or hillside so that the north, and possibly part or all of east and west walls, are sheltered.
- Underground construction: The ground is excavated, and the house is set in below grade.