All houses have some sort of foundation.
The foundation is the portion of the house that is below ground level, and which anchors the house to the earth, spreads the load of the weight of the house, and prevents the house from settling unevenly. Foundations can be minimal and simple in some locales, or can be complex and large where seismic activity is anticipated, where the ground typically freezes several feet below the surface, where the home site is on a hillside, or for other reasons. Other than supporting the house, the most common problem a foundation is asked to solve is frost heaving due to the ground seasonal freezing and thawing. The bottommost part of the foundation is the A footing which is a pad of concrete several times as wide as concrete stub or basement walls, upon which the basement or stub walls rest. While simple, slab footings are notoriously cold for living spaces, are unfriendly to the feet and knees, and use what some feel to be an excessive amount of concrete.