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A yaodong (窰洞) is a dugout used as an abode or shelter in China. Yaodongs are common in north China, especially on the Loess Plateau. The history of yaodongs goes back centuries, and they continue to be used.
Yaodongs are usually carved out of a generally vertical side of a loess hill. If the side is not vertical, it must be cut vertical. The silty soil is soft and easy to dig. The cross section of a yaodong is similar to that of a cave: a rectangle in the lower part connected to a semicircle in the upper part. The width at the floor is from 3 to 4 meters, and the highest point in the ceiling is around 3 meters or higher. The depth of a yaodong can be 5 meters or more. Windows and doors are installed at the opening of the yaodong. The inner side wall is usually plastered with lime to make it white. A platform called a kang is built to be used as a bed. A fireplace is built beside the kang and the smoke and hot gas go through the built-in channels inside the kang to heat it before exiting through a chimney.
The hill that surrounds all but one side of the indoor space serves as an effective insulator keeping the inside of a yaodong warm in cold seasons and cool in hot seasons. Consequently, very little heating is required in winter, and in summer, it is as cool as an air-conditioned room.
More elaborate yaodongs may have a facade built with stones with fine patterns carved on the surface. Yaodongs can also be constructed with stones or bricks as stand-alone structures. Often, three or more yaodongs in a row are constructed. First, stones or bricks are used to build the arch-shaped structure, and then soil is used to fill up the external space above the arches to make a thick and flat roof.
Many thousands of people died in collapsed yaodongs in the 1556 Shaanxi earthquake.
The most famous yaodongs in China are perhaps those in Yan'an. The communists led by Mao Zedong headquartered there in 1935-1948 and lived in yaodongs. Edgar Snow visited Mao and his party in Yan'an and wrote Red Star Over China. An estimated 40 million people in northern China live in yaodongs. 
See also Edit
Golany, Gideon S. Chinese Earth-Sheltered Dwellings. Honolulu: University of Hawaii, Press, 1992.