Every house is built on a foundation, but not every house is built on the same foundation. Depending on factors such as your type of house, geographical location, soil, climate, moisture, and budget, your house foundation will be either a full basement, crawlspace, or slab.
A full basement foundation is the deepest of the three major foundation types. One advantage of building a full basement is that it allows the possibility of doubling your floor space if you eventually finish the basement. A full basement comprises 100% of the floor space of the level above and it is generally at least 6 feet high. A full basement can be conditioned (meaning that its temperature and humidity are controlled by HVAC ducts) or unconditioned. Both the full basement and crawlspace depend on foundation footings around the perimeter, upon which the structure rests. Footings extend a minimum of 12" below grade.
Crawlspaces elevate the house a few feet above the ground--higher than a slab (which lies directly on the ground) and lower than the full basement. Typically, crawlspaces are vented from the outside. But this can lead to moisture problems, which lead to condensation and mold. Alternatively, you can close up the crawlspace and condition it in order to control moisture.
Slab on Grade
Grade refers to ground-level and slab refers to the monolithic concrete pad that rests on the ground. Slab-on-grade foundations have typically been used in climates that do not experience ground freezing and thawing, as this can lead to cracks in the concrete. Slab-on-grade foundations tend to be less expensive than the deep (elevated basement or crawlspace) foundations and better protect against termite infestation. One notable downside of slab foundations is that water supply and drainage pipes are encased in the concrete. In the event of problems, the concrete must be broken up before the repair can take place. Not all slabs are built on grade. Commercial properties and custom homes may be built on elevated concrete slabs.