Guide
Foundation crack types and what they actually indicate
Updated
Crack width is the thing everybody measures and the thing that matters least. Pattern, location and change over time are what tell you whether you have a problem.
The patterns, and what they suggest
- Fine vertical cracks in poured concrete
- Very common, often shrinkage as the concrete cured in its first year or two. Usually not structural. They can still leak, and sealing a leaking shrinkage crack is a waterproofing job rather than a foundation job.
- Diagonal cracks from a corner of a window or door
- Openings are stress concentrators, so differential settlement expresses itself here first. Worth taking seriously, particularly if the crack is wider at one end and if doors in that part of the house have started to bind.
- Stair-step cracks in block or brick
- The crack follows the mortar joints in a staircase pattern. Classic differential settlement, or in a basement wall, a sign of lateral pressure. Note which direction the step climbs and whether one side has moved out of plane with the other.
- Horizontal cracks partway up a basement wall
- The one to act on. A horizontal crack, especially in a block wall around the mid-height, usually indicates the wall is bending under lateral soil pressure. Combined with any inward bow, this is a call to an engineer now rather than at the weekend.
- Wide cracks with vertical offset
- Where one side of the crack has dropped relative to the other, or where the wall has moved out of plane, you have measurable differential movement rather than surface cracking.
- Cracks that reappear after being filled
- Filling a crack does not stop movement. A repaired crack that reopens is evidence the movement is active, and that is genuinely useful information for an engineer.
The symptoms that are not cracks
- Doors and windows binding, particularly if it changes with the seasons, which points at shrink-swell clay rather than a one-off failure.
- Sloping floors, checkable with a long level or a ball. A consistent slope across a room says more than a crack does.
- Gaps opening between trim and ceiling or wall, or nail pops in a line.
- A chimney separating from the house, which often sits on its own footing and settles independently.
- Water entry that started recently, which can mean the wall has moved enough to open a path, or simply that drainage has changed.
How to monitor properly, for free
- Photograph everything, with a ruler or coin in the frame for scale, and with the date recorded.
- Mark the ends of each crack with a pencil line and the date, so any extension is visible later.
- Measure the width at a marked point rather than at the widest point, so you are comparing like with like.
- Repeat monthly for a season, ideally across a wet-to-dry swing, since Missouri clay movement is seasonal.
- Take that record to the engineer. Evidence of rate is the most useful thing an owner can bring, and it can be the difference between a monitoring recommendation and a pier design.
When to stop monitoring and call someone today
A horizontal crack with visible inward bow, a wall that has shifted out of plane, sudden change over days or weeks, a crack that appears alongside new water entry, or any structural movement combined with a suspected sinkhole or slope failure. The Missouri Geological Survey lists earthquakes, sinkholes and landslides among the state's geologic hazards (dnr.mo.gov), and a suspected karst feature under a house is a geotechnical question rather than a repair-product question.
None of this is a diagnosis of your house. It is what to look at and what to record, so that the professional you call arrives with something to work from. Read who to call, and why the order matters next.