What is Bernow soil and how does it affect Oklahoma foundations?

Reviewed by Preston, Oklahoma foundation repair consultant · Updated 2026-10-14

In short: Bernow is a deep, well-drained soil of eastern and southeastern Oklahoma that formed from weathered Cretaceous sandstone. Its subsoil is loam, sandy clay loam or clay loam with roughly 20 to 32 percent clay, far less than the heavy clays that drive most seasonal foundation movement in the state. For a Bernow lot, water management, erosion and fill quality are usually the first things to look at.

Where does Bernow soil occur?

The USDA Natural Resources Conservation Service (NRCS) maintains an Official Series Description (OSD) for every named soil. The Bernow OSD places the series in eastern Oklahoma, and possibly Arkansas, Louisiana and Texas, with its type location in Bryan County about 4 miles northeast of Bokchito ¹. It lies in Major Land Resource Areas 87B (Texas Claypan Area) and 133B (Western Coastal Plain) and is described as moderately extensive ¹.

Bernow forms on hillslopes of dissected plains, on slopes of 0 to 12 percent ¹. This puts it in the Southeast (Ouachitas and Red River) and South-Central (Arbuckles and Texoma) parts of the state, on sandy and loamy material weathered from Cretaceous sandstones ¹.

What are the key properties of Bernow soil?

"Residuum" means soil that weathered in place from the rock below it. The "Bt" horizon is the subsoil layer where clay has built up over time.

Most Bernow land is used for tame pasture or woodland, and native vegetation is mainly oak with a grass understory ¹.

What do these properties mean for foundations?

Lower clay content

Clayey soils swell when they take on water and shrink when they dry, which pushes foundations up and lets them drop as seasons change ⁴. Bernow's subsoil tops out around 32 percent clay and is loam, sandy clay loam or clay loam rather than clay ¹. NRCS rates shrink-swell by linear extensibility percent (LEP), the change in length of a soil sample between moist and oven-dry: under 3 percent is low, 3 to 6 percent moderate, 6 to 9 percent high and 9 percent or more very high ³. The rated LEP for each map unit is listed in Web Soil Survey ².

Water, leaks and erosion

Even on less expansive soils, uneven moisture under a foundation is more damaging than uniform moisture, and leaks in sewer or water lines can cause localized movement ⁴. Bernow is well drained with moderate permeability ¹, and its sandy surface layers lie on hillslopes where runoff ranges from very low to medium ¹. Concentrated water from downspouts or leaks is worth tracing on these lots; see erosion, undermining and washout voids and surface drainage and grading.

Fill and site grading

Fill placed during lot grading is not part of the native Bernow profile that the OSD describes ¹; its behavior depends on how it was placed. See fill consolidation settlement and fill soils and lot history.

How do you check a specific lot?

• Look up the address in Web Soil Survey, which publishes soil data produced by the National Cooperative Soil Survey ².
• Check the map unit's LEP value against the NRCS shrink-swell classes ³.
• Keep soil moisture next to the foundation as uniform as practical: slope soil away from the house and discharge downspouts away from the foundation ⁴.
• Watch for warning signs such as stair-step cracks in brick, sticking doors and sloping floors ⁴.

Related

• Soil Series Index
• Shrink-Swell and Active Zone
• Cretaceous Shales, Clays and Sandstones
• Southeast Oklahoma (Ouachitas and Red River)
• Durant soil