More than two-thirds of new single-family homes built in the U.S. in 2021 were constructed on concrete slab foundations, according to analysis from the National Association of Home Builders. The association analyzed data from the U.S. Census Bureau’s Survey of Construction and determined that slab adoption rates are growing nationally as new single-family home construction increases in Southern states.

According to the NAHB, slabs are most prevalent in Texas, Oklahoma, Arkansas and Louisiana. In those states, slabs accompany more than 96% of new single-family homes as the dominant foundation type.

Unsurprisingly, slab foundations are less common in the Great Lakes region, New England and the northern Midwest. Building on slabs is more cost-effective in warmer climates, according to the NAHB.

The share of new single-family homes being built on slab foundations in the U.S. has increased steadily throughout the years. In 2000, 46% of new homes across the country were being built on slab foundations. In 2021, slab foundations accounted for 67% of foundations for new homes, according to the data.

Conversely, the share of new homes being built with basements has decreased steadily. In 2021, only 21% of new single-family homes were built with full or partial basements—down from 36.8% of new homes in 2000.