How do you tell foundation heave from settlement?

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

In short: Heave is the ground under a foundation rising, usually because clay soil took on water; settlement is the ground dropping, often because clay dried and shrank or soft soil compressed. Both leave a house uneven and can produce similar cracks, so the distinction is made from floor surveys over time, the season, and the water sources around the house. Getting it right matters because the two call for different responses.

What are heave and settlement?

Post-Tensioning Institute (PTI) evaluation guidelines define heave as upward movement of an underlying supporting soil layer and settlement as downward movement of that layer ¹. On expansive clay, heave happens when moisture is added and shrinkage happens when moisture is removed ¹. "Expansive" clay is soil that swells noticeably when wet; the most swelling clays are smectites such as montmorillonite ².

In Oklahoma, the Oklahoma Geological Survey notes that more than 75 percent of the state has bedrock that can produce expansive soils, and that saturation from rainfall, lawn watering or sewer leaks can damage foundations ⁶.

What drives heave and settlement?

Some notes on the table:

• HUD's soil guide states that vegetation can worsen shrinkage during warm, dry periods because plants draw water from the soil ⁵. See tree-root desiccation settlement.
• Lawn and garden watering creates a moist zone along the outside of a foundation, and leaking pipes and pools add water unevenly ². See leak-induced localized heave.
• Because corners of a uniformly loaded slab press on the soil with about a quarter of the pressure at the center, corners tend to lift when the soil swells ². See perimeter wetting heave and center heave.
• ASCE Texas guidelines note that removing a tree can allow soil heave and that a waiting period may be recommended before repair ³; see post-tree-removal heave.

The greatest expansive-soil hazard is in climates with pronounced wet and dry seasons, and a two-year drought followed by an extremely wet year is cited as a problem case ².

Why is a single survey not enough?

An elevation survey maps high and low areas, but PTI notes that unless a benchmark is used, contours alone do not show whether heave or subsidence occurred ¹. A center that reads high could be a center that rose, or edges that fell. The only absolute way to measure movement is to compare two surveys ¹, calculating the change at each matching point ⁸.

Which tests help decide?

• Plumbing tests. ASCE Texas guidelines list plumbing testing as part of a more detailed investigation and say water supply and drain lines should be tested for leaks if lifting is part of the repair ³. The ASCE homeowner guide suggests watching for unexplained increases in water bills and confirming leak repairs with pressure tests ⁴. See plumbing leaks under slab.
• Soil sampling. Site-specific soil sampling is also listed among detailed investigation tests ³; see soil testing and lab values.
• Repeat surveys. Comparing surveys taken at different times shows whether an area is rising or falling ¹⁸.
• Ruling out look-alikes. Ceiling-wall gaps at interior partitions that open in winter and close in summer are often truss uplift, roof trusses bowing as their lumber dries unevenly, not foundation movement ⁷.

Why does the call matter?

Lifting is aimed at raising low areas. If a high area is high because it heaved, raising the surrounding foundation does not address the added water that caused it. ASCE Texas guidelines stress maintaining near-uniform soil moisture and caution against excessive watering ³, and the ASCE homeowner guide notes overwatering itself can cause heave ⁴.

Related

• Shrink-swell and the active zone
• Distress pattern library
• Over-lift heave after drought lift
• Seasonal movement calendar
• Perimeter drying settlement