Aipedia: Structural and civil engineers

LLMs and AI for structural calculations

Aipedia, by the Apex broking team · Last reviewed 2026-10-27

Large language models should not be relied on to produce structural calculations, because CROSS-UK says they are "not inherently calculation engines" and their numbers need competent verification. For engineers, an unchecked AI calc is an unchecked design, with the same liability.

Part of: AI in structural and civil engineering

In short

A language model predicts plausible text; it does not reliably carry out arithmetic, apply load combinations or exercise engineering judgement. CROSS-UK Report 1554 (July 2026) described an AI-written calculation report for heavy rooftop plant that looked robust to a non-engineer but was fundamentally wrong, with fresh errors in each revision. IStructE expects a senior engineer to review any AI-produced structural design, and Part 2A reg 11K requires designers to take reasonable steps so the design would comply if built. PI usually treats a calc error the same way whether or not AI was involved, subject to the wording.

How AI is being used for calculations

Engineers and others around them are using generative AI chatbots to explain code clauses, set out calculation steps, draft calculation narratives and, increasingly, produce whole calculation reports. Some use them to sense-check hand calculations or to convert spreadsheet logic into readable text. Architects and building services designers sometimes use the same tools to estimate structural effects of their proposals, as our guides on architects and AI structural calculations and AI and rooftop plant loads explain.

The risk is not that an LLM is always wrong. It is that it is fluent, formats numbers convincingly and has no reliable way of knowing when it has made an error.

The duties that apply

Part 2A, Building Regulations 2010 (England). Reg 11K requires a designer to take reasonable steps so the design, if built, would comply with all relevant requirements, and to give sufficient design information to others. Reg 11F requires the skills, knowledge, experience and behaviours for the work. Read Part 2A.
IStructE Code of Conduct. Article 5: undertake only tasks you are competent for. Article 6: appropriate skill and judgement, including a quality management system. Code of Conduct.
IStructE AI guidance. A senior engineer should review any AI-produced structural design, and tools should be evaluated regularly against current standards. Implementing AI in structural engineering.
Statement of Ethical Principles. Principle 3 requires accuracy and rigour and work within current competence.

What can go wrong

CROSS-UK Report 1554 is the clearest UK example. Heavy rooftop plant was proposed on an existing reinforced concrete flat-slab building with retail below and flats above. The calculation report, in the reviewing engineer's view largely AI-written, was fundamentally wrong and created a risk of overloading. Each revision introduced new errors, and no competent structural engineer had verified it. The panel said responsibility must stay with suitably qualified structural engineers, cited Part 2A regs 11F to 11H and suggested that AI-assisted outputs be disclosed in submissions.

Illustrative scenario: a small practice uses a chatbot to produce the calculation for a steel beam supporting a new opening. The model omits a point load from a column above and applies the wrong combination factor. The checker reviews layout and presentation but does not recalculate. Cracking appears after completion, propping and remedial steelwork are needed, and the client claims the cost and loss of use.

How PI usually responds

There is no statutory compulsory PI for structural engineers generally; cover is usually required by appointment. A civil liability PI policy commonly responds to a claim alleging the design fell below the standard of a reasonably competent engineer, and the use of AI does not usually change that test. The question will be whether the calculation was negligent, not which tool produced it. Cover still depends on the policy wording, any exclusions, and whether the proposal form accurately described how the firm works. See our structural calculation error scenario and the structural engineers PI guide.

Practical controls

Never issue a number from an LLM without an independent calculation or verified software run.
Record which parts of a calculation package were AI-assisted and who verified them.
Have a senior engineer review any AI-produced design, as IStructE expects.
Check loads and combinations from first principles on every revision, not only the first issue.
Keep junior staff off AI calculation tools until they can show the underlying competence.
Tell clients and Building Control where AI was used, in line with IStructE and CROSS.

How Apex helps

Apex arranges PI for structural engineers. A broker reviews your cover, your appointment limits and how your policy treats AI-assisted calculations.

Sources

Frequently asked

Can I use AI to check my own structural calculations?

You can use it as a prompt to look again, but not as the check itself. An AI that agrees with your numbers proves little. Verification should come from an independent calculation, validated software or a competent engineer who reworks the critical elements.

Who is liable if an AI tool gets a calculation wrong?

The engineer or firm that issues the design. Part 2A reg 11K places the designer duty on the designer, and CROSS says responsibility must stay with suitably qualified structural engineers. Any recovery from a tool supplier is a separate question and depends on their contract terms.

Should I tell Building Control that AI was used?

IStructE says firms should share their AI policy with Building Control, and CROSS-UK suggested designers disclose AI-assisted outputs in submissions and noted approving authorities may ask about it. A short statement of what was AI-assisted and how it was verified is sensible.

Does an AI calculation error void my PI?

Not usually by itself. PI generally responds to negligent professional work regardless of the tool used. Problems are more likely if the proposal form misdescribed your practices or the wording contains a relevant exclusion, so check the policy with your broker.

Check your PI covers how you use AI

Tell us about your firm and the work you do. A broker will review how your current PI treats AI-assisted work, or arrange new cover. No fee for a quote. Or call 0117 325 0027.

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Apex Insurance Brokers Limited is authorised and regulated by the Financial Conduct Authority. Registered in England and Wales, company number 07014570. This page is general information about how AI is used in the profession and how insurance may respond. It is not legal, regulatory or insurance advice on your circumstances, and it does not guarantee that cover will be available or on what terms.