"An important reason why caves are warm in winter and cool in summer is that they have a thick roof. On the top of the cave in northern Shaanxi, pedestrians can ride horses and even push carts. Even brick kilns and earth kilns must be covered with a thick layer of soil to keep the cave warm, just like air conditioning. " In addition, the top and wall of the cave can neither directly absorb heat from the atmosphere nor directly radiate heat to the atmosphere. Only the hole can be in direct contact with the outside world. Therefore, the temperature change in the cave always lags behind the outside world, and the temperature difference changes little. On the northern Shaanxi plateau, a farmer worked hard all his life, and his basic wish was to build several caves. In their view, how the cave is built is related to the good or bad events of future generations. There are differences in caves such as soil, brick and stone, and there are also differences in brick hanging surfaces and stone interfaces. Explains the family background. In the past, before men and women got married, the woman went to the man's house to "see the place", that is, to see how many caves and what materials the other person had, and the other person's family background was clear at a glance. It's easy to repair and dig holes in the soil. In front of a hillside, the cliff was cut and doors and windows were installed, which became a hole kiln. Usually, the life of an earth hole can last for two generations, and then it can't be because the loess layer is gradually peeling off. In the Loess Plateau, thousands of gullies have been formed due to thousands of years of rain erosion. Clay and minerals make the soil here very hard. The loess with a depth of 100-200 meters is extremely difficult to penetrate water and has a strong vertical position. It can be dug at will without collapsing, which provides a good architectural premise for cave dwellings. Most of the kiln roofs of earth caves are tied with wicker to prevent the soil from collapsing. However, in the case of floods or landslides, the danger of collapse is always devastating.