Finding a crack in your basement wall is unnerving, but most aren't emergencies. The direction, width and behavior of a crack tell you a lot about what's going on.
Usually not structural
- Thin vertical cracks in poured concrete. Often from the concrete shrinking as it cured. They can leak, but they rarely mean the wall is failing.
- Short diagonal cracks from window corners. Common stress points; watch them, seal them if they leak.
Worth watching
- Stair-step cracks in block walls. They follow the mortar joints. Thin and stable ones may be settling; wide or growing ones need attention.
- Cracks that get wider. Mark the ends with a pencil and the date, and measure the width. Growth over months is a warning sign.
Get these checked soon
- Horizontal cracks, especially in block walls partway up the wall.
- Walls that bow or lean inward. Hold a level or straight board against the wall.
- Cracks where one side has shifted in or out relative to the other.
These suggest soil pressure is pushing on the foundation. Repairs such as carbon fiber straps, steel bracing or anchors can stabilize the wall, but the sooner it's addressed, the simpler the fix.
Leaks are a separate question
Any crack can let water in. A leaking crack in a stable poured wall is usually sealed with injection from inside. If water pressure behind the wall is high, drainage work keeps it from leaking again.
Take dated photos of any crack you're unsure about. They make it easy for a contractor to see whether it's changing.