Earth sheltering

Earth sheltering is the architectural practice of using earth for external thermal mass against building walls. This is a passive solar practice.

Theory

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.

Most often, there is not an earth covering on the roof, but this is occasionally done.

Earth sheltered homes

Totally underground houses are uncommon, but are usually built around a central atrium which is open to the sky, much like similar homes sometimes built by the ancient Romans.

The majority of earth sheltered homes use earth sheltering around three of the sides and over the roof. The remaining side (facing south in temperate areas of the northern hemisphere and north in temperate areas of the southern hemisphere) is entirely covered with windows to allow passive solar heating and a maximum of natural light from the sun.

In theory, an earth-sheltered home can give better insulation against the elements, reducing heating and cooling costs and also reduce the noise levels coming from outdoors. In practice it is very difficult to design and implement such a house given the issues of water seepage, internal condensation, cave-like acoustics, and the lack of construction companies with experience in building residences underground.

In the 1970s and 1980s, Earth-sheltered homes were popularized by the back to the land movement as a form of self-sufficient homes.

The most famous and probably the largest earth-sheltered home belongs to Bill Gates, who had it built over a period of several years on a heavily wooded site on the shore of Lake Washington. It is an excellent example of the lack of obtrusiveness of this kind of home, since it appears much smaller than it actually is, when seen from the lake.

One of the oldest examples, dating from some 5,000 years ago, can be found at Skara Brae in the Orkney Islands off northern Scotland.

See also

• Malcolm Wells, proponent of earth-sheltered building
• British Earth Sheltering Association