NAHB analysis of the Survey of Construction (SOC) shows that 57% of all new single-family homes started in 2015 were built on slab foundations, 27% had a full/partial basement, and 14% had a crawl space. The remaining 2% included raised supports, earthen, and other foundation types. The share of new single-family homes built on slabs steadily increased from 46% in 2000 to 57% in 2015, whereas basement foundations became less common.
The foundation types for residential construction are closely related to climate conditions, especially the frost line. Homes in colder areas, where building codes normally require foundations built below frost depth, are predominately constructed with full or partial basements. The division with the highest share of full/partial basements is the West North Central (81%), followed by New England (78%), the Middle Atlantic (68%), and the East North Central (64%). However, the share of homes with a full/partial basement is low in the West South Central and the Pacific divisions.
The use of slab foundations is more popular in the West South Central (96%) and South Atlantic (69%) divisions, where the climate is warm and/or clay soil is expansive. Slab foundations are quicker and cheaper to construct, compare to full/partial basements and crawl spaces.
Slab foundations are commonly used in the West region, including the Pacific and Mountain divisions. Nevertheless, the large variation in geography and climates explains different trends of foundation types in these two divisions. In the Pacific division, new single-family homes with full/partial basements are rare, accounting for about 3.2% from 2003 to 2015. The most common foundation is slabs, followed by crawl spaces. In contrast, the share of new single-family homes with full/partial basements in the Mountain division increased to almost 50% by 2015, whereas the share of homes built on slabs declined from 54%, the highest percentage in 2005, to around 42% recently.