down away from the building. The berm can be partial or total. The polar facing wall may be bermed, leaving the equator-facing wall un-bermed (in temperate regions). Usually this type of earth shelter is built on, or only slightly below the original grade. Due to the building being above the original ground level, fewer moisture problems are associated with earth berming in comparison to underground/fully-recessed construction, and it costs less to construct. According to one report, earth berming provided 90-95% of the energy advantage as a completely below grade structure. In-hill The in-hill (also termed "earth covered", or "elevational") construction is where the earth shelter is set into a slope or hillside, and earth covers the roof in addition to the walls. The most practical application is using a hill facing towards the equator (south in the Northern Hemisphere and north in the Southern Hemisphere), towards the aphelion (north) in the Tropics, or east just outside the Tropics. There is only one exposed wall in this type of earth sheltering, the wall facing out of the hill, all other walls are embedded within the earth/hill. This is the most popular and energy efficient form of earth shelter in cold and temperate climates. Underground The true underground (also termed "chambered" or "subterranean") earth shelter describes a house where the ground is excavated, and the house is set in below grade. They can feature an atrium or courtyard constructed in the middle of the shelter to provide adequate light and ventilation. The atrium is not always fully enclosed by raised ground, sometimes a U-shaped atrium is used, which is open on one side. With an atrium earth shelter, the living spaces tend to be located around the atrium. The atrium arrangement provides a much less compact plan than that of the one or two-story bermed/in hill design; therefore it is commonly less energy efficient, in terms of heating needs. Therefore, atrium designs are found mainly in warmer climates. However, the atrium does tend to trap air within it which is then heated by the sun and helps reduce heat loss. Atrium designs are well suited to flat sites, and are fairly common. Other types Depending on what definition of earth sheltering is used, other types are sometimes included. In culvert homes ("Cut and Cover"), precast concrete containers and large diameter pipes are arranged into a connecting design to form a living space