Surprisingly there are already millions of people living underground due to the lack of space above ground. An example of this is in Singapore, which is one of the most crowded countries on the planet. Its population of nearly 5.5 million people is squeezed into a city state that covers just 710 sq km. It is also used in communities with extreme environments such as Italy’s Sassi di Matera, Australia’s Coober Pedy and the Berber caves in Matmâta, Tunisia. Underground living is even being considered for the design of a future base on Mars. With today’s technologies one can direct natural light into living spaces with light tubes. Often, underground living structures are not entirely underground, typically they can be exposed on one side when built into a hill. This exposure can significantly improve interior lighting, although at the expense of greater exposure to the elements.
Some of the advantages of underground houses include resistance to severe weather, quiet living space, an unobtrusive presence in the surrounding landscape, and a nearly constant interior temperature due to the natural insulating properties of the surrounding earth. The greatest appeal for most is the energy efficiency and environmental friendliness of underground dwellings. Initial building costs are often low, as underground building is largely subtractive rather than additive, and because the natural materials displaced by the construction can be recycled as building materials. However, underground living does have certain disadvantages; such as the potential for flooding, which in some cases may require special pumping systems to be installed. Also for a small percentage of people, the mere thought of being underground in a confined space can be terrifying, about 3% of people are severely claustrophobic – not having a clear way out or being fearful of flooding or fires can cause a lot of stress.