The efficiency of earth-covered houses

An earth-covered house provides one of the most energy-efficient forms of shelter imaginable. Here are some facts you'll want to know if you'd like to consider an earth-covered home.

Underground architecture is attracting more and more attention from solar heating experts and others interested in making the utmost of the sun's output. Earth-covered houses are recognized as the most thermally efficient form of passive solar building in temperate climate regions.Whatever the weather outside, the inside temperature at floor level varies by only a few degrees annually, so that mechanical heating and cooling can, in all but the most extreme conditions, be kept to a minimum.

Even in extremely cold or overcast conditions, it's unusual for temperatures to drop more than 5°C below a level that requires heating. Additional heat is generally provided by using passive solar design methods. In warm climates, a solar-efficient design and a proper covering of earth are enough to maintain a comfortable internal temperature for most of the year.

The regions in which earth-covered houses are most efficient are those with the greatest difference between day and night temperatures and/or summer and winter temperatures. This means that the closer an earth-covered house is to the equator, the less efficient it is at maintaining a comfortable temperature.

The thermal system of a house built into hillsides is deceptively simple. North-facing windows are double glazed or at least heavily insulated by double curtains and pelmets or external insulated shutters. These are combined with skylights, courtyards or covered atriums depending on the climate and aspect to ensure that the sun's rays are able to penetrate the house. The buried walls facing in other directions act as a heat source or sink to provide heat to the interior, or absorb heat from it depending on the season and time of day.

During the winter, solar heat gain from the rooms facing north will build up and be absorbed into the internal and earth-contact walls; as the temperature drops during the evenings, heat will be re-radiated back into the rooms. In summer, heat is excluded from the building by carefully designed sun shading of all glazed areas. During summer evenings, when the air is cool, the building is opened up to natural ventilation and the heat-bank wall system flushed of its daytime heat build-up.

Proper ventilation is essential for an earth-covered house to be effectively cooled. The house should be designed to take advantage of any breeze that springs up. With air circulating freely throughout all areas of the house, moisture build up is prevented and there is little chance of condensation occurring. All internal areas where moisture is produced artificially (such as kitchens and bathrooms) must be fitted with efficient exhaust fans to the outside to minimize the potential for condensation on cool wall surfaces.