Short answer
The strongest signs come in groups: new cracks plus doors or windows that stick, floors that slope enough to notice, or cracks with one side higher than the other. A single sign alone is weak evidence. Many cracks, nail pops and binding doors have other causes. An engineer's elevation survey decides whether the slab moved.
Key facts
- Cracks are more likely to be a structural concern when they come with inoperable doors and windows or excessively sloping floors, per NAHB.[2]
- FPA says floor slopes of 1% or more may be noticeable, and it recommends slab tilt stay at or below 1%.[1]
- FPA lists doors that bind at the bottom but open easily when lifted by the knob as a loose or undersized hinge problem, not foundation movement.[3]
How engineers group the signs
The Foundation Performance Association (FPA) sorts distress into three tiers[1]:
- Architectural (cosmetic): cracks and separations. In concrete or masonry they usually become noticeable at about 0.04 in wide; in drywall and stucco, at about 0.02 in[1].
- Functional: doors or windows that stick, will not close, or swing on their own; noticeable floor slopes or wall tilt; tilted countertops; pavement offsets high enough to trip on[1].
- Structural: a framing or foundation member can no longer carry its design load with an adequate safety margin[1].
Most homeowners see the first tier. The second tier is what makes an engineer's visit worthwhile. NAHB guidance puts it this way: cracks alone do not necessarily mean a structural concern. They are more likely to be one when they come with inoperable doors and windows or excessively sloping floors, or when one side of the crack has moved vertically[2].
Signs that point toward slab movement
| Sign | Why it matters | Source |
|---|---|---|
| Several doors start sticking in the same season as new cracks | Functional distress plus cracking | [1][2] |
| Floor slope you can feel or see with a marble or level | FPA says slopes of 1% or more may be noticeable | [1] |
| A crack where one side sits higher than the other | Vertical offset can indicate a structural concern | [2] |
| Cracks that keep getting wider | Active movement, not a one-time shrinkage crack. NRMCA advises professional evaluation of cracks widening with time | [5] |
| Gaps between walls and ceiling or floor that open and close with the seasons | Typical of clay that swells and shrinks with moisture | [4] |
| Cracks that appear after a leak, a drought, or a big tree goes in or comes out | Moisture change under the slab is the usual driver in clay areas | [4] |
FPA's guideline sets a recommended tilt limit of 1% over the full length, width or diagonal of the slab, and a deflection limit of L/360[1]. Those limits only apply after an engineer has taken a floor elevation survey[1]. A salesperson's quick reading with a handheld level is not the same thing.
Look-alikes: signs often blamed on the foundation
FPA's structural committee published a table of distress that is often mistakenly blamed on foundation movement[3]. A selection:
| What you see | More likely cause (per FPA) | Usual fix |
|---|---|---|
| Door binds at the bottom but opens easily when you lift the knob | Loose or undersized hinge | Tighten or replace hinge screws[3] |
| Nail pops, crown molding gaps, drywall tape cracks in a newer house | Wood framing drying and shrinking | Wait about two years, then repair[3] |
| Brick cracks over a wide garage door opening | Lintel undersized or overloaded | Reinforce or replace the lintel[3] |
| Brick cracked 1 to 2 ft above the slab next to the garage door jamb | Hit by a car bumper | Repair brick and jamb[3] |
| Small spalled chip at a slab corner under brick | Brick bonded to the grade beam and moved with heat | Cosmetic patch[3] |
| Random hairline cracks in the slab with no distress above | Shrinkage as the concrete cured | Wait until dormant, then repair as needed[3] |
| Hairline cracks in tile or grout in a newer home | Slab still shrinking under the tile | Wait until dormant, then replace tiles[3] |
| Floor out of level with no cracks anywhere | Slab may have been built that way | Monitor elevations, for example quarterly[3] |
The last row matters. FPA found most slabs are built within 1.0 inch of level[1]. A floor can be uneven from day one. Without a baseline, one survey cannot prove it moved.
What to do this week
- Document. Use the crack assessment checklist. Photograph each crack with a ruler or crack card in the frame, and date it.
- Mark crack ends with a pencil and the date. Recheck in a month and again next season.
- Check water. Look for downspouts that empty at the slab, soil that slopes toward the house, ponding, or a sprinkler spraying the slab edge. FPA says drainage must move stormwater away from the foundation for most repairs to work[4].
- Check plumbing. A rising water bill, a warm spot on the floor, or a damp area with no source can mean a slab leak. Leaks under the slab are a known cause of movement[4].
- Read the crack width guide before you assume width alone decides anything.
What not to conclude
Do not treat any single symptom as proof of foundation failure. Do not treat a free inspection from a company that sells piers as a diagnosis. The deciding evidence is an elevation survey plus the distress pattern, read by an engineer. See how slab foundation repair works for the evaluation levels.
When to call a pro
- Doors or windows start sticking and new cracks appear in the same season: call a structural engineer.
- A crack shows a vertical offset or keeps widening between your dated marks.
- You suspect a slab leak: call a licensed plumber first, then an engineer if cracks follow.
- You are buying or selling a home with visible slab distress: get an engineer's report, not just a contractor's estimate.
More questions
My floor is out of level but nothing is cracked. Is that a problem?
Not necessarily. FPA notes the slab may have been built out of level. Its suggestion is to monitor slab elevations, for example quarterly, to confirm there is no ongoing movement.
Are cracks in floor tile a sign of foundation movement?
Often not. FPA traces many tile and grout cracks in newer homes to concrete that kept shrinking after the tile went down. Wait until the cracking looks dormant, then replace tiles.
Sources
- FPA-SC-13-1: Guidelines for the Evaluation of Foundation Movement for Residential and Other Low-Rise Buildings (Rev. 1, Apr 2015), Foundation Performance Association, Structural Committee. Accessed 2026-10-06.
- Misconceptions about the common crack (Builder Education Series), National Association of Home Builders (Walt Keaveny, PE, PG). Accessed 2026-10-06.
- FPA-SC-03-1: Distress Phenomena Often Mistakenly Attributed to Foundation Movement (May 2004), Foundation Performance Association, Structural Committee. Accessed 2026-10-06.
- FPA-RC-01-0: Post Foundation Repair Performance of Residential and Other Low-Rise Buildings on Expansive Soils (Jan 2004), Foundation Performance Association, Repair Committee. Accessed 2026-10-06.
- CIP 7: Cracks in Residential Basement Walls (2014), National Ready Mixed Concrete Association. Accessed 2026-10-06.
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