In Arizona we typically have two general types of concrete foundations:

Slabs/Mono-pour Slabs are most common in warmer areas such as Florida, Arizona, California and Texas. Since there is often a shallow frost line, or no frost line at all the footings and slab can be poured right on top of the ground. The footings and slab can often be poured at the same time. When the footings and slab are poured together it is called a monolithic slab.

Stem Wall SlabWhere a slab is desired for cost savings or otherwise in a cold climate a stem wall/slab foundation is the choice. The footings and foundation are constructed like a crawlspace foundation. Fill is placed inside the foundation and is compacted. The slab is then poured. Sand bags are used occasionally instead of fill.

CrawlspaceCrawlspace is more popular in moderate climates such as the Pacific Northwest, the mid-Atlantic coast. The footings are placed below the frost line, and a stem wall is placed on top of the footing. The sub-floor structure is placed on top of the foundation.

Basements are most often built in cold weather climates such as the Northeast, Midwest and Rocky Mountains. The footings in these colder climates need to be below the frost line which is fairly deep in these areas. Basements provide the cheapest square footage in most instances. The upfront cost of basements is high, but the cost of the square feet that is gained is comparatively inexpensive. Check your area for basements. If basements are popular in your area, not having one may make your home harder to sell. There are three types of basements standard, walkout and daylight. Standard basements are not accessible by the outside and don't have exposed basement walls. Daylight basements have one or more walls exposed, and are typically built on hillsides. Walkout basements have access via an exterior door and staircase to the outside.