Why your house foundation is cracking
Sunnyvale’s expansive clay swells when wet and shrinks when dry. If one side of the house sits in soggy soil (under a downspout, at a low spot) and the other stays dry, the foundation gets pushed unevenly. Over years, that shows up as cracks. How clay soil works →
Homes built before about 1945 often have concrete with no steel reinforcement, and crack more easily.
Is a foundation crack normal?
Usually fine, keep an eye on it:
- Hairline cracks, thinner than a credit card
- Vertical cracks that aren’t getting wider
- Cracks that showed up in the first year or two after the concrete was poured
When to worry about foundation cracks
Have it checked if you see:
- Cracks wider than 1/8 inch
- Horizontal cracks in a foundation wall
- Diagonal or stair-step cracks
- Cracks that are getting wider, or one side higher than the other
- Cracks along with doors or windows that stick, gaps at the ceiling, or sloping floors
A simple test: mark the ends of a crack with a pencil and the date. Check after the next few storms and again in late summer. Growth means movement.
Why drainage comes first
If water is pooling next to the house, fixing the foundation without fixing the water treats the symptom. Control the water first, then decide whether the foundation needs work.
Start here:
When you fill out our form, tell us about any cracks. If it looks like more than a drainage job, we’ll match you with a contractor who does both.
Common questions
Is a foundation crack normal?
Hairline and vertical cracks that aren’t growing are usually cosmetic. Cracks wider than 1/8 inch, horizontal or diagonal cracks, growing cracks, or cracks with sticking doors and sloping floors should be checked.
Why is my house foundation cracking?
In Sunnyvale, expansive clay swells when wet and shrinks when dry. Uneven moisture around the house, often from downspouts or low spots, pushes the foundation unevenly and causes cracks.
Are foundation cracks covered by insurance?
Usually not when the cause is soil movement or settling. Check your policy.
Do foundation cracks get worse in summer or winter?
Clay movement is seasonal. Some cracks open in late summer when the clay shrinks and close a little in winter when it swells. That’s why tracking a crack across both seasons is useful.
Who should I call about a foundation crack?
For small cracks with an obvious water source, a drainage contractor. For wide, horizontal or growing cracks, a foundation contractor or a structural engineer.
Get a free estimate from a licensed contractor →
Sunnyvale Drainage Help is a free referral service, not a contractor. Contractors pay us for referrals. How it works · Updated 2026-10-26