NAHB analysis of the Survey of Construction (SOC) shows that 65% of all new single-family started in 2020 were built on slab foundations, followed by 22% with a full/partial basement and 12% with a crawl space. The gap between slab and full/partial basement foundation adoption rates is growing: the share of new homes built on slabs steadily increased from 46.0% in 2000 to 65% in 2020, while the share of new homes with basements dropped from 36.8% to 22%.
New homes with slab foundations are most common in the West South Central (95.7%), South Atlantic (79.4%), Pacific (67.7%), and Mountain (48.1%) divisions. These are most popular in the West South Central division where new single-family homes have been primarily constructed on slab foundations over the past ten years. A warmer climate makes building on slab more cost-effective, compared to full/partial basements. Slab foundations also need the least amount of maintenance in the long run. In the East South Central division, 43% of new homes started in 2020 had a crawl space and 38.0% were built on slabs.
There are large regional differences in foundation types across the nation. Homes in colder areas, where building codes normally require foundations to be built below the frost line, are predominately constructed with full or partial basements. The division with the highest share of full/partial basements in new homes is New England (79.8%), followed by the West North Central division (77.2 %), the Middle Atlantic division (69.5%), and the East North Central division (54.3%). In these divisions, full/partial basement foundations offer additional finished floor areas at a marginal increase of construction cost. The average area of finished basement was 1,156 sq. ft. in the East North Central division, 998 sq. ft. in the West North Central division, 921 sq. ft. in the Middle Atlantic, and 734 sq. ft. in New England. Nationwide, the average finished floor space of basements was 1,137 sq. ft. in 2020.