NAHB analysis of the Survey of Construction (SOC) shows that 67% of all new single-family homes started in 2021 were built on slab foundations, followed by 21% of homes built with a full/partial basement and 11% of homes built with a crawl space. As home building shifts towards the southern divisions, the slab adoption rates are growing larger. The share of new homes built on slabs steadily increased from 46% in 2000 to 67% in 2021, while the share of new homes with basements dropped from 36.8% to 21%.
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. As a result, in the northern divisions, full/partial basement foundations offer additional finished floor areas at a marginal increase of construction cost. The division with the highest share of full/partial basements in new homes is New England (78.7%), followed by West North Central (76.1%), Middle Atlantic (63.5%), and East North Central (53.5%). The average area of finished basement was 1,125 square feet in East North Central, 1,088 sq. ft. in the West North Central division, 822 sq. ft. in New England, and 778 sq. ft in the Middle Atlantic. Nationwide, the average finished floor space of basements was 1,170 sq. ft. in 2021.
New homes with slab foundations are most common in the West South Central (96.2%), South Atlantic (82.7%), Pacific (73%), and Mountain (46.5%) divisions. 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, 42.2% of new homes started in 2021 had a crawl space and 39.6% were built on slabs.
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