Why is my foundation cracking?
Many foundation cracks come from the soil, not the concrete. Clay soil swells when it's wet and shrinks when it dries out, so long wet spells followed by droughts push and pull on a slab or piers. Poor drainage makes it worse by soaking one side of the house more than the other. Thin hairline cracks are common and often harmless. Wide cracks, cracks that keep growing, or sticking doors and sloping floors mean the house is moving and needs a foundation specialist.
- Urgency
- Address soon
- DIY
- Call a professional
- Typical cost
- $500–$10,000
- Time
- An hour or two to inspect
Hairline cracks that aren't changing can be watched. Get it looked at soon if cracks are wider than about a quarter inch, growing, uneven from side to side, or showing up with sticking doors, gaps at trim, or sloping floors.
What's happening
Clay soil changes volume with moisture. When one part of the soil under the house is wetter or drier than another, the foundation is lifted or dropped unevenly, and the stress shows up as cracks in the slab, brick, drywall or around doors and windows.
Most likely causes
- 01Swelling and shrinking clay
Wet seasons swell the soil and dry spells shrink it. The more the moisture swings, the more the house moves.
- 02Water collecting on one side
Bad slope or downspouts at the wall soak one side of the foundation while the rest stays drier.
- 03Trees near the house
Large trees pull moisture out of the soil during dry weather, shrinking it under the nearest part of the foundation.
- 04Plumbing leaks under a slab
A leaking drain or supply line under the slab can soften the soil in one spot.
- 05Normal curing and settling
Thin cracks in a new slab are usually concrete shrinking as it cures, and are not a sign of movement.
What you can safely check before they arrive
- 1Photograph each crack with a tape measure or coin for scale, and date the photo
- 2Mark the ends of the crack with a pencil so you can see if it grows
- 3Note any doors or windows that started sticking and when
- 4Check that gutters and downspouts carry water away from the house
- 5Do not fill or patch the crack before a specialist sees it. Patching hides what they need to measure
When to call someone
Call a foundation specialist or structural engineer if cracks are wide, growing, or come with sticking doors, sloping floors or gaps around windows. An independent engineer's report is worth having before you sign any repair contract.
What it should cost
$500–$10,000
An engineer's inspection is often $300 to $800. Fixing drainage around the house can be $1,000 to $6,000. Underpinning with piers commonly costs several thousand dollars and up, depending on how many are needed.
Estimates are typical US ranges for orientation. Actual pricing varies by region, home and contractor — always get a written quote.
What happens if you wait
Movement that's left alone usually keeps going. Small problems turn into cracked pipes, broken tile, doors that won't close and much larger repair bills, and active foundation problems can hurt resale value.
Questions to ask the contractor
- Is this crack from movement, or from normal settling and curing?
- Has a structural engineer looked at it, and can I see the report?
- Will fixing the drainage alone help, or do I need piers?
- How many piers, how deep, and what warranty comes with them?
- Is the warranty transferable if I sell the house?
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Last reviewed November 8, 2026. General guidance only — it can't replace an inspection of your actual home by a qualified professional.