Structure
There is a crack in my foundation. Is it serious?
The honest version of this article is shorter than most: some cracks are normal, some are not, and the difference is not something to diagnose from a photo.
Most concrete cracks. Fine hairline cracks in a slab or foundation wall are extremely common and frequently harmless. What a general contractor can honestly do is observe and describe — width, pattern, whether it is moving, and whether the rest of the house shows related signs. Whether a crack is structurally significant is a determination for a licensed structural or geotechnical engineer, not for a builder. Anyone who tells you a foundation is fine, or not fine, without that assessment is guessing with your house.
Why we will not diagnose this for you
We hold a California General Building (B) licence. That covers building, and it is the right licence for the work we do. It is not a structural engineering licence, and structural determinations belong to engineers for good reason: they carry professional liability for that judgement and they have the analysis to back it.
So this page will not tell you whether your crack is serious. It will tell you what we look at, what tends to matter, and when the answer is clearly “get an engineer out now” — which is genuinely useful and is as far as we can honestly go.
We are a builder. If your foundation needs work, that is work we could bid. That is exactly why we do not want to be the one who decides it needs work. An independent engineer's assessment protects you from us as much as from anyone else.
What we look at on a walk-through
- Width. Hairline is different from a crack you can fit a coin into. Width is the first thing anyone measures, and it is measured rather than eyeballed.
- Pattern and direction. Vertical, diagonal and horizontal cracks tend to come from different causes. A stair-step pattern through block or brick reads differently again.
- Displacement. Are the two sides still in the same plane, or has one side moved relative to the other? Movement is a different conversation from a crack.
- Whether it is active. A crack that is stable is not the same problem as one that is still opening. This is why monitoring over time is often the first recommendation rather than repair.
- Corroborating signs elsewhere. Doors and windows that stick or have been re-hung, sloping floors, separation at wall and ceiling joints, cracks repeating above openings. A foundation issue rarely shows up in one place only.
- Water and drainage. Where the water goes is frequently part of the story, and it is often the cheapest part to address.
Signs that mean stop reading and call someone
These are not diagnoses. They are the observations that, in our experience, warrant an engineer promptly rather than at your convenience:
- A crack you can fit a coin into, or one that is visibly wider at one end than the other
- A horizontal crack running along a foundation wall, particularly with any inward bowing
- One side of the crack sitting proud of the other — visible displacement
- A crack that has measurably changed since you first noticed it
- Doors or windows that have gone out of square recently rather than gradually over decades
- Visible sloping or bounce in a floor that was previously flat
- Any of the above appearing after an earthquake, a plumbing leak, or significant landscaping or drainage work nearby
A wide crack that has looked identical for twenty years and a narrower one that appeared last winter are not the same finding. If you are unsure, photograph it against a ruler with today's date and do it again in a few months. That record is genuinely useful to whoever assesses it.
Who to actually call, and in what order
| Professional | What they determine | When you want them |
|---|---|---|
| Structural engineer | Whether it is structurally significant, and the repair design | Any of the signs above, or before buying a house with visible foundation cracking |
| Geotechnical engineer | What the soil is doing underneath | Where movement is suspected, on expansive soils, or on a slope |
| General contractor (us) | What the repair will cost and how it gets built | After there is an engineer's determination to build to |
| Foundation repair specialist | A proposed repair method | Useful — but be aware they are quoting the fix they sell. An independent engineer's assessment first is the protection |
The order matters. An independent assessment first, then bids against that assessment, is how you avoid buying a solution to a problem nobody confirmed you had.
How this shows up in a remodel
Foundation questions surface constantly in our actual work, because opening a house up is when you finally see what is under it. A second-storey addition depends entirely on whether the existing foundation and walls can carry the load — and that is an engineering answer, which we coordinate and price rather than guess at.
Where a project turns out to need foundation work, it goes in the proposal as its own line item, built to an engineer's design, and inspected. It does not get folded quietly into another number.
Common questions
Are hairline cracks in a slab normal?
Can you tell me from a photo?
How much does a structural engineer's assessment cost?
Should I just seal the crack?
Do you do foundation repair?
Where to go next
Written by the team at Elusive Construction, a licensed California general contractor (B #1112902) building in Santa Clara and San Mateo counties. General information about how residential construction works — not legal advice. For your specific contract, talk to an attorney.
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