Design Considerations

To take full advantage of earth sheltering it is necessary to design the house with an eye to increasing the passive solar gain of the house. Minus the jargon this basically means that the house should be oriented such that it receives the maximum possible winter sun and as little as possible summer sun (this depends somewhat on the particular climate). An elevational type design (A3, B3) is ideal from this point of view because all (or most) exposed surfaces face in one direction. The direction in which the house should be 'pointed' varies with latitude, but fundamentally houses in the southern hemisphere should face north and houses in the northern hemisphere should face south.

The reason this is the case is because although the sun never changes which direction it comes from (basically north or south) the angle at which it hits the earth sheltered home changes throughout the year. In winter the sun is low in the sky and thus hits the sunside of the house at a low angle. In summer the sun is high in the sky and hits the house from more like directly above. e.g.

As the above diagram hopefully illustrates,the angle at which the sun hits the house in winter allows sunlight and heat to penetrate deep into the house. Conversely, in summer the overhang of the roof blocks all sun from entering the house and thus keeps the house cooler.

All this heat entering the house during winter days is great, but what about winter nights which are surely colder than winter days? The crucial part of passive solar design is trapping the sun's heat once it has entered the house, and this is where earth sheltered homes stand out above conventional houses.

Objects with high mass, such as rocks have a much greater capacity for storing heat than objects with low mass. In an earth sheltered house all or most of the external walls are directly connected to earth which has a very good capacity for storing heat, the internal walls are also likely to be made of poured concrete or masonry which also has a considerable capacity for heat storage. In addition to this the floor and ceiling are both often (always in the case of the floor) in contact with the earth and are also made of heavy materials. All in all an earth sheltered house has a considerable capacity to store heat which it receives from the sun. In contrast a conventional home, even one built on a concrete slab, has much less mass and therefore much less capacity to store heat. The end result of this stored heat is that come winter night in an earth sheltered house, heat actually radiates from the walls, floor and ceiling and warms the house.

This has been a very basic overview of passive solar design. Passive solar design is an energy efficient style of building construction in its own right, and therefore before you build any new home you should seek more information on this very important topic.

[ Top ]

Something that should be briefly mentioned is the exterior surface area of a building. The following diagram shows two floor plans, Plan A. and Plan B. which both enclose the same floor space but have a differing amount of wall area in contact with the outside world.

The units here are irrelevant, what is relevant is the fact that Plan B. has a larger wall area while enclosing the same floor area. This demonstrates the fact that a compact design can reduce the amount of surface area which a building has in contact with the outside. (N.B. This principle also works in three dimensions.) The more surface area a house has in contact with the outside, the more heat it will lose through these surfaces. This leaching of heat is reduced in an earth sheltered house but is still worth consideration. In cold climates it will be desirable to reduce the surface area of the walls, floor and roof in order to minimise heat loss. However, in hot climates, it will aid the cooling of the house if the surface area is increased. In both cases the 'compactness' of the design should be noted and adjusted to suit the conditions if this is acceptable to those who will live in the house.

[ Top ]