Engineer negligence claims: design-liability examples
Reviewed by Apex Insurance Brokers · Last reviewed 2026-08-05
Structural, civil, mechanical and building-services engineers all carry design responsibility, and with it the risk of a negligence claim. Most disputes are not about collapsed buildings — they are about calculations that had to be redone, specifications that did not meet a standard, or advice a client relied on and lost money over. The examples below are anonymised and illustrative, but each reflects a common pattern in how design-liability claims arise and how PI cover responds. Engineering consultancies reviewing their current broking arrangement can read about our engineers professional indemnity broking page.
What "design liability" actually means
A design-liability claim alleges that the engineer failed to exercise the reasonable skill and care expected of a competent member of the profession. That is the test at common law and, for most services contracts, under the Supply of Goods and Services Act 1982 (or the Consumer Rights Act 2015 where the client is a consumer). It is a negligence standard — not a guarantee that the design will be perfect.
Trouble often starts when a contract quietly raises that bar. A "fitness for purpose" obligation asks the engineer to warrant an outcome, which is a stricter promise than reasonable care and is frequently excluded by PI policies. Reviewing appointment wording before you sign is one of the cheapest risk controls available to an engineering practice.
Anonymised design-liability examples
These scenarios are composite illustrations, not real firms or cases.
- The structural miscalculation. A structural engineer sizes a steel transfer beam for a mixed-use development. A loading assumption is carried over from an earlier scheme and never rechecked. The error surfaces during building control review, forcing a redesign, delayed steel fabrication and a contractor's prolongation claim. The client pursues the engineer for the added cost and programme loss.
- The wrong specification. A building-services consultancy specifies a ventilation product that does not meet the performance criteria the client's brief required. The mistake is caught after installation. The remedial cost — stripping out and replacing plant — becomes the basis of the claim, along with the disruption to a live building.
- The missed ground condition. A civil engineer designs foundations relying on a limited site investigation. Variable ground is later encountered, requiring redesigned piling. The client argues the engineer should have recommended further investigation before committing to a foundation solution. Whether that is negligence or simply the realisation of a known ground risk becomes the central dispute.
- The reliance on a third party. A lead engineer coordinates a design that incorporates a specialist sub-consultant's element. When that element fails to perform, the client sues the lead practice as the party it appointed. The lead firm then has to consider recovering against the sub-consultant — a reminder that collateral warranties and sub-consultant PI matter.
- The drawing that did not match the intent. A mechanical engineer's issued drawings contain a routing clash that the contractor builds as drawn. The rework is modest in isolation, but the claim bundles in delay, professional fees and the client's management time.
Notice the common thread: the headline error is often small, but the loss is driven by downstream consequences — delay, rework, third-party claims and fees. That is why even a "minor" design mistake can generate a claim well into six figures.
Reviewing your appointment terms or renewing cover? Get an engineer's PI quote built around your actual design exposure.
Get a PI quote →How professional indemnity insurance responds
A PI policy is written on a "claims made" basis. What matters is that the policy is in force when the claim is made or a circumstance is notified — not when the design work was done. That has two practical consequences: you must keep cover running after a project completes (through renewal or run-off), and you must notify circumstances promptly, before they harden into a formal claim.
When a valid claim is notified, the insurer typically funds:
- the legal defence, including solicitors and expert engineers;
- damages or a negotiated settlement, up to the limit of indemnity;
- claimant costs awarded against you, subject to the policy terms.
You retain the excess, and cover is capped at your limit of indemnity. Whether that limit applies to each claim or in the aggregate over the policy year is a key term to check.
Where cover can fall short
| Situation | Why it can be a problem |
|---|---|
| Fitness-for-purpose clause | Often excluded — the policy covers negligence, not guaranteed outcomes. |
| Late notification | Failing to report a known circumstance can prejudice or void a claim. |
| Limit too low | Remedial plus consequential loss can exceed a modest indemnity limit. |
| Uninsured sub-consultants | If they cannot pay, the loss stays with the practice that appointed them. |
| Gap in run-off cover | Claims arrive years after completion; without run-off, there is no policy to respond. |
Generic limits such as £1m, £2m or £5m are common starting points, but the right figure depends on project values, contract requirements and the consequential losses your designs could trigger. A limit that suits a small residential practice may be nowhere near enough for a firm doing structural work on large commercial schemes. Talk to a broker before defaulting to a round number — start a quote here.
Reducing the risk of a claim
- Use clear written appointments and avoid accepting fitness-for-purpose or uncapped liability by default.
- Keep an auditable design record — assumptions, calculations, checks and sign-offs.
- Operate a genuine second-pair-of-eyes review on critical calculations.
- Manage the client's brief and scope changes in writing, so reliance is documented.
- Notify your insurer of circumstances early — a phone call before a claim, not after.
Common questions
Does PI cover an honest mistake, or only serious negligence?
It covers civil liability arising from a breach of professional duty — which includes ordinary errors, not just gross failings. The test is whether reasonable skill and care were exercised, so a genuine but negligent mistake can be covered.
How long after a project can an engineer be sued?
Under the Limitation Act 1980, contract claims generally run for six years, and negligence claims can run longer depending on when the damage was discoverable. This is why maintaining PI or run-off cover well past project completion matters.
What should I do the moment a client raises a design concern?
Do not admit liability or promise to put it right for free. Notify your broker or insurer as a potential circumstance straight away, and preserve your project records. Early notification protects your position under a claims-made policy.
Apex Insurance Brokers Limited is authorised and regulated by the Financial Conduct Authority (FRN 724952). This guide is general information, not advice on a specific policy or a substitute for your policy wording.