Foundation Crack Checklist: Stair-Step, Horizontal, Hairline
This page helps you describe what you're seeing so a professional can assess it. It isn't an engineering assessment. When in doubt, especially with any sign of structural movement, have a structural engineer or experienced foundation professional look at it.
Before you start: what you need
- A flashlight and phone camera
- A tape measure or a crack-width card (a coin works for rough comparisons)
- A pencil or painter's tape to mark crack ends
- A 4-foot level (for walls and floors)
- A notebook or the notes app, with dates
Step 1: identify the crack type
Hairline vertical cracks (poured concrete walls)
Thin, roughly vertical cracks, often running from the top of the wall or around a window. Many are caused by concrete shrinking as it cured. They are commonly considered lower priority if they're thin, dry and not growing.
Diagonal cracks
Running at an angle, often from a window corner or near a wall end. These can point to differential settlement, with one part of the foundation moving more than another.
Stair-step cracks (block or brick)
A zig-zag following the mortar joints. Kansas City contractors call these especially common in KC block walls (Olson). They can come from settlement or from soil pressure on the wall.
Horizontal cracks
Running sideways partway up a basement wall, often around the frost line or mid-height. These are typically linked to soil pressure pushing the wall inward. Treat a horizontal crack, especially with any bowing, as a reason to get a professional assessment rather than waiting.
Slab and floor cracks
Cracks in the basement floor or a slab-on-grade. Many are shrinkage cracks; vertical displacement (one side higher than the other) is the thing to note.
Step 2: measure and record
For every crack:
- Photograph it with something for scale, and note the date.
- Mark both ends with a pencil line and the date. If it grows past the mark, you'll know.
- Measure the widest point. Write it down.
- Check for offset: is one side of the crack higher, or pushed further in, than the other?
- Check for water: damp edges, efflorescence (white mineral deposits), or staining.
- For walls: hold a level vertically against the wall near the crack. Note any lean or bow.
- Re-check in 4–8 weeks, and again after a big wet spell or a freeze.
Step 3: check the warning signs
Note any of these. Each makes a professional look more worthwhile:
Priority guide
This is a way to organize your next step. It's not a diagnosis.
| What you see | Suggested next step |
|---|---|
| Single hairline vertical crack, dry, not growing | Mark, photograph and re-check over the next few months. Consider sealing if it ever leaks. |
| Hairline crack that leaks water | Get it looked at; crack injection is a common fix (see costs below). Check gutters and grading too. |
| Stair-step crack, stable | Professional inspection when convenient; monitor monthly. |
| Stair-step crack, widening, or with sticking doors | Schedule an inspection soon. |
| Horizontal crack, or any bowing | Schedule a professional assessment soon; consider a structural engineer. |
| Rapid change, a wall moving visibly, or doors suddenly jammed | Contact a professional promptly. If you're worried about safety, keep people out of the area until it's assessed. |
What repairs typically cost
- Crack injection: $250–$800 per crack nationally (HomeGuide); one KC contractor lists epoxy injection at $40–$50 per foot (Olson).
- Bowing walls: see carbon fiber vs beams vs anchors.
- Settlement (piers): see pier installation cost in KC.
- An inspection or engineer's report: HomeGuide lists foundation inspections at $400–$750 and engineer reports at $500–$3,000. Some contractors offer free inspections, but a contractor's inspection isn't the same as an independent engineer's opinion.
Plug crack counts into the estimator for a ballpark.
Download-style checklist
Copy this into your notes:
Crack #__ Location: __________ Wall/floor: ____ Material: poured / block / brick
Type: hairline / diagonal / stair-step / horizontal / slab
Width (widest): ____ Length: ____ Offset: Y/N Water: Y/N
Wall plumb (level): OK / leaning ____ in
Date marked: ____ Re-check 1: ____ change? __ Re-check 2: ____ change? __
Other signs: doors sticking / floor slope / exterior brick cracks / gaps