NAHB analysis of the Survey of Construction (SOC) shows that 60.1% of all new single-family started in 2018 were built on slab foundations, followed by 24.3% with a full/partial basement, and 14.3% 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 60.1% in 2018, while the share of new homes with basements dropped from 36.8% to 24.3%. The increasing gap is largely driven by the declines of the basement foundation adoption rates in New England and the Middle Atlantic divisions.
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 West North Central (81.8%), followed by New England (69.5%), and Middle Atlantic (57.3%). 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 1,050 square feet in the West North Central division, 884 sq. ft in the Middle Atlantic, and 727 sq. ft in New England. Nationwide, the average finished floor space of basements was 1,115 sq. ft. in 2018.
New homes with slab foundations are most common in the West South Central (96.9%), South Atlantic (72.9%), Pacific (63.4%), and Mountain (43.7%) 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. Warmer climate makes building on slab more cost-effective, compared to full/partial basements. Slab foundation also needs the least amount of maintenance in the long run.
In the East South Central division, 46.9% of new homes started in 2018 had a crawl space and 31.3% were built on slabs. Since 2003, the share of new homes built with crawl space increased from the lowest level of 17.6% in 2004 to the highest of 47% in 2017. On the contrary, the share of homes built on slab foundation declined from the highest of 61.0% in 2004 to the lowest of 31.3% in 2018.