Is My Foundation Crack Serious? How to Tell

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Not every crack is a crisis — but some are. Here's how to read them.

Usually cosmetic

• Thin vertical or diagonal cracks (less than about 1/8”) from normal concrete curing and minor settling.
• Hairline cracks in plaster or drywall above doors and windows.

Take seriously — get it inspected

• Horizontal cracks in a foundation wall — often a sign of soil or water pressure pushing the wall in.
• Stair-step cracks in block or brick.
• Cracks wider than 1/4”, or ones that are getting wider over time.
• Cracks with bowing walls, sticking doors/windows, or uneven floors.

Why foundations crack

The biggest culprit is the soil. Expansive clay swells when wet and shrinks when dry, putting relentless pressure on walls — it's one of the leading causes of foundation movement in the US. Freeze–thaw cycles, poor drainage, and plumbing leaks add to it. (See which US metros carry the most risk in our Basement Water Risk Index.)

What to do

Mark the ends of a crack with a pencil and date it; if it grows, act. Non-structural cracks are often sealed with epoxy or polyurethane injection; bowing or structural issues may need carbon-fibre straps or steel reinforcement. Compare at least two quotes from local foundation repair pros.

General guidance only — a professional on-site inspection is the only way to diagnose a structural problem.

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