air infiltration within an earth shelter can be advantageous. Because three walls of the structure are mainly surrounded by earth, very little surface area is exposed to the outside air. This alleviates the problem of warm air escaping the house through gaps around windows and door. Furthermore, the earth walls protect against cold winter winds which might otherwise penetrate these gaps. However, this can also become a potential indoor air quality problem. Healthy air circulation is key. As a result of the increased thermal mass of the structure, the thermal lag of the earth, the protection against unwanted air infiltration and the combined use of passive solar techniques, the need for extra heating and cooling is minimal. Therefore, there is a drastic reduction in energy consumption required for the home compared to homes of typical construction. Wind protection The unique architecture of earth houses protects them against severe windstorms. They cannot be torn away or tipped over by strong winds. Structural engineering and, above all, the lack of corners and exposed parts (roof), eliminate vulnerable surfaces which would otherwise suffer from storm damage. Natural resource saving Compared with the material needs of standard buildings, earth-sheltered homes can greatly reduce the number of natural resources. Traditional wood structure home requires lumber for framing and interior finishes, which is quite a big demand. Soil as the main building material and blending in with the landscape, earth-sheltered houses drastically reduce the demand for lumber. Biological effects Earth homes organically embrace animals and poultry as well as water, soil, and plants. Arcology studies the relationship between animals and plants and man-made buildings during ecological development. For example, raising poultry and domesticated animals is an important part of the traditional Chinese rural human settlements and these elements create a stable and sustainable ecological cycle that benefits the environment. Landscape protection and land use Compared to conventional buildings, earth houses can fit into their surroundings. The soil-covered roofs hide the building within the landscape. Some claim that the construction method is advantageous to the nitrogen-fixation of the soil on the roof, because it would otherwise be covered by the foundation of a traditional house. Contrary to conventional roofs, earth-house roofs allow plants to grow semi-naturally on them. Such houses can also be built as terraced structures on a slope in hilly terrain. Fire protection Compared to other building materials, such as wood, earth houses feature efficient