Earth sheltered homes as an option reserved exclusively for the inhabitants of Hobbiton
Earth sheltered homes are energy efficient because they benefit from the constant thermal mass of the soil. Whilst surface temperatures fluctuate with the seasons, the earth stays at around a steady 15 degrees Celsius. So occupants benefit from a cooling effect in the summer and heating effect in the winter. By using this passive solar method on its own, energy bills can be cut by 80% but a 50% reduction is still said to be possible if used in conjunction with conventional heating and cooling methods.
Earth sheltered homes don’t mean has to be underground.
Earth sheltered homes can be built above ground and then covered with earth or alternatively they can be built into a hill-side so that the front facade of the property can be constructed the same as any traditional properties.
What I’ve never been convinced about with earth sheltered homes construction is the ability to prevent the ingress of damp? The standard practice is to construct the property in reinforced concrete with the waterproofing membrane fixed to the outside of the concrete in several layers. In theory, it's not much different to applying a damp proof course in a regular home - a thick layer of impermeable material acting as a barrier between the earth and the structure.
Even though there are some obvious benefits to an earth sheltered home there are also some risks as is the case with any experimental housing technology. Which is why at the end of the day most of us will stay as surface dwellers for at least a little while longer and the idea of eco-towns full of earth sheltered homes is some way off.