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.
Are the basements finished with a concrete floor? And isn’t that somewhat akin to a slab at ground level? But maybe also akin to an insulated crawl space (just a taller space, tall enough to be useable for living space)? The data is interesting; it would be helpful to learn why the slab is preferred. Less labor? Less expensive materials? Improvement in suitable floor coverings? Or other reasons that explain the dramatic increase.
I’d say its the stability of the structure and the number of foundation repairs that are made through the years. Slab with a turn down, (monolithic slab) is a far superior foundation and has many more times the strength than the footer and block or poured wall systems. Rebar and a solid foundation will very rarely require anything for 50+ years if done right. Look at everyones steps in these states that don’t do slabs. They all sink because they’re not tied in with bar and concrete. An all in one is not much more intensive but contractors have been cheap for far too long and the cost is relatively the same, cancels out pretty much.
What about slabs in earthquake prone areas?
We are looking for an area to purchase a new home with slab on grade foundation that has been built in the last 5 years in an high desert climate. We looked in the greater Denver area and it seems as though most everything is crawl space or full basement. In Boise, just about all newer homes are crawl space. The only place we’ve found is Arizona, but it’s just too hot. What other areas would you recommend we investigate?