Sinking Foundation in Houston: Settlement, Subsidence or Clay?

Is my house really sinking?

Sticking doors, cracked brick or drywall, and floors that feel out of level are on the checklist on our signs of foundation problems page. None of them tells you on its own which way the slab moved, or why.

Settlement, subsidence and heave

The Foundation Performance Association (FPA) defines three kinds of vertical movement (FPA-SC-13-1, Guidelines for the Evaluation of Foundation Movement, 2015, checked 2026-10-17):

• Settlement: soil moving down because the load from above is more than it can bear. It includes compression of the soil, slope instability, erosion, fault movement and slow consolidation of saturated clay, and it can happen in any soil.
• Subsidence (in the engineering sense): soil moving down because it lost moisture and shrank. It normally happens in clay, often from drying by trees or other large plants, especially in drought.
• Heave: clay swelling as it takes on water, pushing that part of the foundation up. Heave is the reverse of subsidence.

So a "sinking" corner might really be the rest of the house rising. The same guidelines say that without a fixed reference point, elevation contours alone may not show whether heave or subsidence happened.

Why Houston clay moves with the seasons

The association's maintenance guide says expansive soils, usually clay, swell when they absorb moisture and shrink when they lose it, and that going from dry to saturated can change soil volume a great deal. It says this movement doesn't mean the foundation was badly designed or has failed, and that uniform soil moisture all around the foundation is the key to less distress (FPA-SC-07-0, Foundation Maintenance and Inspection Guide, 2003, checked 2026-10-17). The guide also says trees near the foundation cause the majority of foundation problems needing repair in this area: trees removed during construction tend to cause heave in the first few years, while trees planted later tend to cause subsidence as they mature, often ten to twenty years on.

Houston clay soil: "gumbo," and what's actually under the city

Where "gumbo" comes from. USDA's Natural Resources Conservation Service says Houston Black, the Texas state soil, formed from Cretaceous clays and marls, is dark, and is sticky and moldable when wet, which is why it's often called "black gumbo" (USDA NRCS, Soils – Texas, checked 2026-10-17). Despite the name, its official series description places Houston Black in the Blackland Prairies and eastern Grand Prairies of east-central Texas (USDA Official Series Description, Houston Black, checked 2026-10-17), so USDA's description doesn't place it on the Gulf Coast prairie around Houston, where the Lake Charles and Beaumont series below are described. The coastal clays. For Southeast Texas, USDA describes the Lake Charles series as an extensive clay found mainly between the Colorado and Trinity Rivers, formed in clayey deposits of the Beaumont Formation on broad coastal prairies. It is moderately well drained but very slowly permeable, and in most years its dry-season cracks stay open for a combined 60 to 90 days (USDA Official Series Description, Lake Charles, checked 2026-10-13). East of the Trinity, the Beaumont series is a poorly drained, very slowly permeable clay of the Gulf Coast Prairie (USDA Official Series Description, Beaumont, checked 2026-10-17). Soil maps work at a broad scale; only a soil test tells you what's under a particular lot. What engineers say about it. The Foundation Performance Association's maintenance guide says much of the clay in the Houston area, especially south of Interstate 10, is expansive, and that its movement can mean either loss of support or tremendous upward pressure on a foundation. It adds a less obvious problem: where low-permeability clay lies a few feet below sand or silt, water can get trapped above it in a perched water table, and that saturated soil can lose much of its bearing capacity, letting the foundation settle (FPA-SC-07-0, Foundation Maintenance and Inspection Guide, 2003, checked 2026-10-17). How it's measured. Engineers rate a clay's potential to change volume with the plasticity index (PI). The association's homebuyers' guide calls clay with a PI under 15 non-expansive, 15 to 25 moderately expansive, and above 26 highly expansive. It suggests asking whether the foundation was designed by a professional engineer based on a site-specific soil report, which is where a PI would be reported (FPA-SC-06-0, Homebuyers' Guide for Foundation Evaluation, 2005, checked 2026-10-13).

Houston subsidence and the Harris-Galveston Subsidence District

There's a second, much bigger kind of sinking. The Harris-Galveston Subsidence District says it was created by the Texas Legislature in 1975 to regulate groundwater withdrawal in Harris and Galveston counties to end subsidence, and that groundwater withdrawals in the region have led to the land sinking (Harris-Galveston Subsidence District, checked 2026-10-17). The District publishes an interactive map built from satellite radar (InSAR) and GPS station data. Regional subsidence lowers whole areas of land at once; it isn't evidence that any one slab has a problem, so treat it as background.

How an engineer tells which one you have

The association's monitoring guidelines assume an initial survey of floor elevations and of cracks and other distress, then describe repeating those surveys over time to see whether movement is still happening, whether it has likely stopped, and why it occurred, and say repairs made after movement has likely ceased carry less risk of distress coming back (FPA-SC-12-0, Guidelines for Evaluating Foundation Performance by Monitoring, 2006, checked 2026-10-17). Its test-methods paper covers tools such as plumbing leak tests, which are often run to confirm or rule out movement caused by leaks below the slab (FPA-SC-02-0, Test Methods for Evaluating Existing Foundations, 2010, checked 2026-10-17). See our foundation inspection guide for what that visit looks like.

Things that look like sinking but aren't

The association says not all distress in Texas homes on expansive soil comes from foundation movement. One example it lists: brick cracks above a long opening, such as a garage door, can come from an undersized or overloaded lintel rather than the slab, and the fix is to reinforce or replace the lintel (FPA-SC-03-1, Distress Phenomena Often Mistakenly Attributed to Foundation Movement, 2004, checked 2026-10-17).

Repair options, briefly

Slab work. The association's repair committee says foundation repair usually includes stabilization, through methods such as changing the foundation support, underpinning with deeper support, or perimeter barriers (FPA-RC-01-0, Post Foundation Repair Performance, 2004, checked 2026-10-17). Our slab foundation repair page walks through them. Piers. One kind of deep support has its own page: helical piers. Pier-and-beam homes. Houses with a crawl space are covered on pier and beam foundation repair. Leveling. See house leveling. Post-tension slabs. If your slab has steel cables, read post-tension slabs and have a professional engineer involved before anyone drills or cores. Prices vary by method and house; see the published ranges on our cost page.

Quote requests are coming soon. For now, call (832) 646-1494 or email [email protected].

When quote requests open, the contractor we refer you to will pay us for each referral; you pay us nothing. We're not a contractor.

Permits in the City of Houston

The Houston Permitting Center says a residential repairs permit is required for repairs that replace or repair existing structural members and other building elements, and that work needing a building permit must be inspected by a structural inspector, including a foundation inspection; the Structural Inspections section is at 832.394.8840 (Houston Permitting Center, Structural Inspections, checked 2026-10-17).