For centuries, the people in very hot climate have used varieties of underground homes to stay comfortable. Recently, due to the rising cost of heating and cooling, homeowners begin to consider the advantages of underground homes. There are very few insulating materials more effective than plain soil. At a certain depth, the temperature of the earth always stays around 50 degrees Fahrenheit. And only a few feet down from the surface, the earth tends to be more comfortable than the air above. This margin of comfort can be quite substantial. An underground home in Minneapolis would be cool already in the summer; in the winter, it would be easier to heat with warm soil packed around it rather than subzero winds whistling around its corners. There are several different approaches to constructing underground homes to take advantage of this energy efficiency. Some homes are built entirely underground, with only a few vents and an entry door. But many people miss windows, so they develop berm homes, which are built into the side of a hill so that one side of the construction is left uncovered. Yet, some architects point out that underground homes will require much stronger roofs to support a soil layer, and drainage must be planned very carefully to ensure that ground water does not seep into the home. Underground homes may be more expensive to build. However, the cost of a properly designed underground home will eventually be lower. There is no sliding to repaint and replace, and there are very few windows to keep in good repair.