Foundation repair contractors offer free inspections. Those inspections are competent and they are performed by people whose business is selling repairs.
A structural engineer is paid for the assessment and sells nothing else. That difference is the entire reason to hire one.
What an engineer produces
Floor elevations across the whole house, plotted, which establishes the shape of the movement and whether it is dishing or doming.
An opinion on cause — settlement, heave, lateral pressure, or something unrelated to the foundation at all.
A recommendation, which may be repair, may be drainage work, and may be to monitor for twelve months and measure again.
A defined scope where repair is warranted: how many piers, where, and what type.
A written report, which is a document you own and can show to any contractor.
Why the scope matters more than the diagnosis
Contractor quotes on the same house routinely differ in pier count, not just in price. That is not necessarily anyone acting badly — different people make different assumptions about load and about how far to extend past the damage.
With an engineer's scope in hand, every contractor bids the same work, and three prices become comparable for the first time.
Without it, comparing quotes means comparing different jobs by their totals.
When to call one
Any horizontal crack, or a wall bowing inward. Different mechanism, more urgent, and not a piering question.
Cracks over about a quarter inch, or cracks on multiple walls.
Doors and windows that have started binding, particularly if it happened recently.
Before buying a house with any visible foundation issue.
Before a repair, when the quoted number is large.
When two contractors disagree substantially about what is needed.
When you probably do not need one
Hairline vertical cracks in a poured wall with no other symptoms. A single crack that has not changed in years. Cosmetic cracking in a house with no functional problems.
Those are monitoring situations. Mark, measure, photograph, and look again in six months.
Cost, in context
An engineer's assessment runs a few hundred dollars in most markets — a small fraction of a repair that commonly runs into five figures.
It is also the only expenditure in the process that might return the answer "nothing needs doing," which no free inspection is structured to produce.
Finding one
Look for a licensed professional engineer with residential foundation experience, and specifically one who does not also perform repairs or take referral fees from repair companies. Ask directly; a straight answer is a good sign.
Some engineers offer a limited visual assessment and others a full elevation survey with a report. For anything that might lead to a repair, the survey and the written report are what you want, because the report is what the contractors will bid against.
After the repair
An engineer can also verify the completed work against the specified scope and sign off that it was installed as designed. On a large repair, and particularly where a house may be sold later, that letter is worth having in the file alongside the contractor's warranty.
What the report should contain
A useful report names the cause, not just the symptom. "Differential settlement at the south-east corner, consistent with shrinkage of expansive clay during the drought period" is actionable; "foundation movement observed" is not.
It should include the elevation plot, photographs, the recommendation, and where repair is recommended, the scope: number of piers, positions on a plan, type, and whether the intent is stabilisation or lift.
It should also state what was not inspected — engineers are explicit about this, and it is a mark of a careful report rather than a limitation.
Buying a house with foundation cracks
This is the single situation where the cost of an engineer is most obviously justified. A visible crack can mean nothing or it can mean a five-figure repair, and a general home inspector will usually recommend exactly this — a specialist opinion — rather than making the call.
Where a seller has had repairs done, ask for the engineer's report, the contractor's scope, and the warranty document, and check whether the warranty transfers to you. All three should exist; frequently only the last is offered.