What causes center heave in an Oklahoma slab foundation?

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

In short: Center heave is when the clay soil under the middle of a slab-on-grade house slowly gains moisture, swells, and pushes the center of the floor up. It is driven by expansive clay plus a water source such as a plumbing leak, and it can look almost identical to the edges of a house sinking. Elevation surveys over time and a check for leaks are how the two are told apart.

What is center heave?

A slab-on-grade foundation is a concrete floor poured directly on the ground. These slabs are flexible enough that they tend to follow the shape of the soil beneath them as it moves ¹. When the middle of the slab rises, engineers call it "center lift" or center heave, and they link it to a long-term gain in soil moisture, typically seen in older foundations ¹.

The soil involved is expansive clay: clay that swells when it takes on water and shrinks when it dries. Clay soils do not move if their moisture stays constant, but in practice moisture rarely stays constant, and it is the change in moisture that causes damage ¹.

How does center heave develop?

• The slab covers the soil. Soil under a house is shielded from the weather, so its moisture can differ from soil that is exposed outside ².
• Water reaches the soil under the center. Common sources include leaking pipes, landscape irrigation, poor drainage and groundwater ¹. Leaking water or sewage pipes add water to nearby soil and can worsen swelling damage ².
• The clay swells. As the soil under the slab swells, the slab moves with it, and because the swelling is uneven the movement is differential, meaning one area rises more than another ¹.
• The house distorts. Differential movement of a slab causes wallboard and brick cracking and skewed door and window frames ¹.

This kind of movement is usually slow. It builds over years rather than a single season, unlike edge movement, which engineers tie to seasonal or temporary moisture changes ¹.

Why are Oklahoma soils prone to center heave?

A 2017 Oklahoma State University study using USDA soil survey data found that nearly all of Oklahoma has medium or high swelling potential, and that more than 75% of the state's bedrock units are possible sources of expansive soils ³. The same study estimated the active zone in Oklahoma, the depth of soil whose moisture changes with the climate, at roughly 0.5 to 4 meters (about 1.5 to 13 feet) ³.

Earlier OSU testing of five western Oklahoma benchmark soils found their fine clays dominantly montmorillonite, a smectite clay that swells strongly when wet, with the Kirkland subsoil dominated by it and rated high in shrink-swell potential ⁴. Soil surveys rate this behavior using linear extensibility, the percent change in length of a soil clod as it dries:

The USDA notes that above 3%, shrinking and swelling can damage buildings and roads and special design is commonly needed ⁵. You can read more about soil types in the shrink-swell and active zone guide.

What signs often go with center heave?

Signs that commonly appear include:

• an interior floor hump near the middle of the house
• ceiling-wall separation at interior walls
• diagonal drywall cracks at door and window openings
• floor tile cracks running in a line
• an unexplained high water bill when a supply leak is feeding the soil

Is it center heave or edge settlement?

Center heave and perimeter drying settlement can both leave a floor that is high in the middle. The difference is which part actually moved.

A single elevation survey shows the foundation's shape at one moment; repeated surveys over months or years show how that shape is changing, and an original-construction survey is useful when one exists ⁷. Without a baseline survey, the amount of movement cannot be determined accurately, partly because most residential slabs are built only to within about 1 inch of level ⁸. See elevation surveys for how this is done, and compare with perimeter drying settlement.

How is the water source found?

The U.S. EPA describes a simple whole-house leak check: read the water meter, use no water for two hours, and read it again; a change suggests a leak ⁶. The EPA also notes that a family of four using more than 12,000 gallons a month in winter probably has a leak ⁶. Texas engineering guidelines call for water supply and sanitary drain lines to be tested for leaks whenever lifting is part of a foundation repair ⁷.

How is center heave typically addressed?

• Remove the water source. Leaks found during testing are repaired ⁷.
• Monitor. The Texas ASCE guidelines note that non-structural measures followed by monitoring may be prudent before, or instead of, structural repairs ⁷.
• Cosmetic repairs. An owner may choose periodic cosmetic repairs and door adjustments rather than full underpinning ⁷.
• Underpinning and lifting. Where lifting is used, the guidelines say it is governed by field judgment and is unlikely to produce a perfectly level foundation ⁷.

Lifting methods such as mudjacking adjust foundation elevations ⁷; they raise low areas rather than lower an area that is already high. The plumbing leak detection and repair and monitoring program pages cover these steps in more detail.

Related

• Leak-Induced Localized Heave
• Perimeter Drying Settlement (Edge Drop)
• Plumbing Leaks Under Slab
• Slab on Grade
• Interior Floor Hump