With extreme weather battering all parts of the globe, now might be the time to bring earth homes back. One foot of soil has an R-value of anywhere from less than R 0.125 to R 0.25 per inch, depending on the soil composition, moisture content, etc R-value is the capacity of an insulating material to resist heat flow. The higher the R-value, the greater the insulating power. 

Exterior of an earth house, built by Peter Vetsch

Depending on the season and time of day, the temperature at the earth's surface may vary considerably, while underground, temperatures are blunted. In winter, the temperature below the surface is higher than at the surface, and in summer, it is cooler. At a depth of 4m, the soil temperature becomes constant.

Throughout most of the US, the temperature 1-1.5m down and below the frost line, is a nearly constant 7.2-10C in northern latitudes, and in southern latitudes, it is 10-21C.

The constant temperature of the earth allows earth houses to have minimal heating and cooling, and this results in a drastic cut in energy costs when compared to typically constructed homes. Another advantage of earth homes is that they provide protection against severe winds and storms which are increasingly more common due to global warming.

Earth homes offer increased protection from wildfires because they are primarily constructed from reinforced concrete. Earth homes also fare better during earthquakes because they are designed to move along with the earth. By placing the excavated dirt onto the roof of an earth house, the roof becomes a garden where residents can grow their own food.

In busy urban areas, earth homes offer increased privacy from neighbours and soundproofing, which can be very beneficial near busy motorways.

History of earth houses

Humans have been living partly in the ground for millennia. By about 15,000 BC in Europe, some migratory hunters were building 'round houses' that were partially sunk into the ground and covered with turf. Examples of this type of construction, which date to 5,000 years ago, can be found in Skara Brae in the Orkney Islands off the northern coast of Scotland.

In the southwestern US, homes built in Mesa Verde National Park, a UNESCO World Heritage Site located in Colorado, took advantage of natural ledges and caves within the earth. Most native American tribes constructed earth-sheltered structures, called 'earth lodges', and across the Great Plains, sod houses known as 'soddies' were common.

In October 1973, the members of the Organization of Arab Petroleum Exporting Countries, which was led by Saudi Arabia, proclaimed an oil embargo as punishment for nations who the organisation felt had helped Israel during the Yom Kippur War of that year. The countries targeted were: Canada, Japan, the Netherlands, the UK, and the US, with the embargo later extended to include Portugal, Rhodesia, and South Africa.

By the time the embargo ended in March 1974, the price of oil had risen nearly 300%, which is referred to as the 'first oil shock'. A second oil shock came in 1979, and this is when, combined with a growing interest in alternative lifestyles and the back-to-the-land movement, interest in earth houses took off.

In the US, most earth houses were built between 1979 and 1983, and the first International Conference on Earth-Sheltered Buildings was hosted in Sydney, Australia in 1983. While earth houses quickly fell out of favour with the US public, they continued to be popular in Russia, Japan, and China, with an estimated 10 million people in northern China living in earth homes.

Beginning in 1974, Swiss architect Peter Vetsch began creating over 50 'Earth Houses' including nine houses that comprise the Lättenstrasse in Dietikon. Vetsch's homes feature domed roofs and rigid foam insulation, and they are surrounded by around 3m of soil. 

Earth house in Dietikon, Switzerland Source: Roland zh/Wikimedia Commons

Vetsch's designs feature buildings that are incorporated into the surrounding landscape, and they include large windows at the front, providing the homes with lots of natural light.

In the US, Earthship Biotecture sells its 'Earthships', which are passive solar earth shelters made out of both natural and recycled materials, including tires. Earthships are intended to be 'off-the-grid-ready' homes that don't rely on public utilities and fossil fuels, but instead utilise energy from the sun. Most Earthships are clustered in New Mexico.

Types of earth houses

Building an earth house usually requires extensive excavation, an increased need for damp-proofing compared to traditional homes and, depending on the design, materials that are designed to stand up to greater weights. One type of earth house is similar to regular home construction, only the home is countersunk into the ground, with windows located just beneath the roof.

A second type of earth house, called 'earth bermed', uses banked earth against the home's exterior walls, and this earth then slopes away from the building. In earth-bermed homes, the polar-facing wall is usually bermed while the equator-facing wall is usually level with the ground.

Since earth bermed houses are built only slightly below ground level, they have fewer moisture problems than other underground structures, and they cost less to construct.

A third type of earth house is 'in-hill', where the home is set into a slope or hillside, with earth covering both the walls and the roof. If this sounds to you like the homes of the Hobbits in JRR Tolkien's Lord of the Rings books which were brought to life in the films by Peter Jackson, they are.

In-hill homes are favoured in cold and temperate climates, and most are built with the opening facing towards the equator.

Another type of earth home, known as 'subterranean', homes are built completely below ground and they often feature an atrium or courtyard in their centre which provides both light and ventilation. These types of houses are most commonly found in warmer climates such as Morocco and Tunisia (the interiors of Luke Skywalker's childhood home on planet Tatooine were filmed in an underground hotel in Matmata, Tunisia).

The last type of earth house is called 'cut and cover', and it features the use of buried containers, such as shipping containers, or precast concrete containers including large-diameter concrete pipes. In 1989 in Japan, the Taisei Corporation submitted plans for a cut and cover project called Alice City, however, it was never built.

Benefits of earth homes

Living roofs better withstand UV rays and temperature fluctuations than conventional roofs. The stable indoor temperatures within earth homes reduce energy costs and the need to burn fossil fuels, so they are better for the environment in this respect. Earth homes require less maintenance than conventional homes, and home insurance costs may be less. Many insurance companies even offer discounts and incentives for 'green' homes.

This article was written by Marcia Wendorf and first appeared in Interesting Engineering.