Net zero advisory and engineer PI: where the exposure is building
Why this is a cluster, not a single risk
“Net zero advice” is not one service. It covers whole-life carbon assessment, operational energy modelling, retrofit strategy, feasibility studies for heat and power systems, decarbonisation roadmaps for estates, and the supporting reports that clients then quote in planning submissions, funding applications and marketing. Each of those has a different failure mode and a different route to a claim, which is why it is worth treating as a family of exposures rather than a single line item on a proposal form.
What they share is a long tail. Advice given at design stage is tested against measured outcomes once a building is occupied, which may be several years later — and by then the standards, the metrics and often the client’s ownership will have changed.
The performance gap
The most predictable source of dispute is the difference between how a building was modelled to perform and how it performs in use. Design-stage models rest on assumed occupancy, assumed operating hours, assumed set points and assumed maintenance. Real buildings depart from all four. Where a client has relied on the modelled figure — in a business case, a lease negotiation or a funding covenant — the shortfall becomes a loss looking for a defendant.
The defensible position is usually available at the time the advice is given, and consists of writing down what the model assumes, what it does not represent, and what would have to be true in operation for the modelled figure to be achieved. Advice that survives is advice whose limits were stated in the report rather than in a later witness statement.
Assumptions, inputs and the duty to explain
Carbon and energy work depends heavily on datasets and factors that are themselves revised: emissions factors, embodied carbon coefficients, grid decarbonisation trajectories, discount rates on future energy prices. Using a superseded factor is a straightforward error. Using a current one without recording which version was used is a slower problem, because it makes the advice impossible to reconstruct when it is challenged.
Where an engineer is one of several consultants feeding a single output, the apportionment question follows quickly. See net contribution clauses in construction appointments and joint and several liability across professional teams.
The standards are moving
A voluntary industry standard now exists for net zero carbon claims about buildings. A pilot version of the UK Net Zero Carbon Buildings Standard was released in September 2024, and Version 1 was published on 10 March 2026. It was developed collaboratively by CIBSE, the Better Buildings Partnership, BRE, the Carbon Trust, the Institution of Structural Engineers, LETI, RIBA, RICS and UKGBC, and verification services were announced for the second quarter of 2026. Adoption is voluntary: the Standard is not a legal requirement, and describing a building as meeting it is a claim capable of being tested. Our page on specialist engineers PI broking covers scoping, presentation and negotiation in turn.
The exposure for advisers is straightforward. A client who is told that a design is aligned with a named standard, and who then relies on that in public or in a transaction, has an obvious complaint if the alignment does not hold up when verified. Where advice references a standard, it is worth being explicit about which version, which scope and which stage of design is being assessed. Further reading: ESG and sustainability advice as a PI exposure and climate risk advice.
Greenwashing allegations
Consumer protection law reaches environmental claims. The consumer provisions of the Digital Markets, Competition and Consumers Act 2024 came into force on 6 April 2025, giving the Competition and Markets Authority direct enforcement powers over misleading claims, including the ability to impose penalties of up to 10 per cent of global turnover. The CMA’s Green Claims Code remains the practical guidance on what an environmental claim has to be able to support.
Most engineers do not make claims to consumers. The exposure is indirect: the consultant’s report becomes the evidence base for a claim the client makes, and when that claim is challenged the consultant is the first person the client turns to. The mitigation is again documentary — being clear about what the analysis supports and what it does not, and about whether the output was intended for publication at all.
The contractual traps
Professional indemnity responds to negligence: a failure to exercise reasonable skill and care. It is not, as a rule, a performance guarantee. Net zero work attracts wording that quietly crosses that line — commitments that a design “will achieve” a stated energy or carbon outcome, fitness for purpose obligations, or warranties tied to a certification result. Those obligations can be uninsured, which is a worse outcome than an uninsured excess, because the firm carries the whole of it.
Three checks are worth making before signing. Is the standard of care expressed as reasonable skill and care, and only that? Are any performance figures expressed as estimates based on stated assumptions rather than commitments? Is there a liability cap, and does it interact sensibly with the PI limit? See engagement letter liability caps and standard of care versus strict liability.
Scope of duty and how loss is measured
Even where advice was wrong, the adviser is answerable for the consequences of it being wrong — not for every loss that flows from the project. That is the principle restated in Manchester Building Society v Grant Thornton, applied to design work in our note on scope of duty in engineer PI claims. Technology-led projects show the same pattern from a different angle in CIS General Insurance v IBM, where the contractual allocation of loss did most of the work.
Notification, because this is a long-tail exposure
Performance shortfalls surface after handover, sometimes long after. Professional indemnity is written on a claims-made basis, so the policy that responds is the one in force when the claim or circumstance is notified — not the one in force when the advice was given. Firms taking on net zero advisory work should be alert to early signals: a client querying measured consumption, a verification exercise that does not confirm expected results, a request to revisit an earlier report. Our notes on what and when to notify, notifications versus claims and preserving privilege set out the mechanics.
Where the work touches higher-risk buildings, the Building Safety Act regime sits alongside all of this — see our hub on the Building Safety Act and professional indemnity and the note on the principal designer role.
Related entries
ESG and sustainability advice: PI exposure · Climate risk advice · Scope of duty: engineers · Scope of duty: architects · Net contribution clauses · Joint and several liability · Liability caps · Standard of care vs strict liability · Principal designer under the BSA · Notifying a circumstance
Frequently asked questions
Does professional indemnity insurance cover net zero and carbon advice?
A professional indemnity policy responds to civil liability arising from the provision of professional services, so advisory work on carbon and energy performance normally falls within it — provided the business description on the schedule reflects what the firm actually does. The risk is not usually the subject matter; it is a performance guarantee or fitness for purpose obligation in the appointment, which sits outside the negligence trigger the policy is built around.
What is the performance gap and why does it generate claims?
It is the difference between modelled design-stage performance and measured performance in use. Models rely on assumed occupancy, operating hours, set points and maintenance, and real buildings depart from those assumptions. When a client has relied on the modelled figure commercially, the shortfall turns into a claim. Recording the assumptions and the limits of the model in the report itself is the main defence.
Can an engineer be caught by greenwashing rules?
Consumer protection enforcement is aimed at the party making the claim to consumers, which is usually the client rather than the consultant. The realistic route to a consultant is indirect: the client makes a public claim on the strength of the consultant’s report, the claim is challenged, and the client looks to the consultant. Being explicit about what the analysis supports, and whether it was intended for publication, reduces that exposure.
Should net zero advisory work be declared to PI underwriters?
Yes. The business description and the activity split drive both the rating and the cover. A firm that has moved into sustainability consultancy without telling its insurers has a presentation problem as well as a cover problem, because the duty of fair presentation runs to every material circumstance about the risk.
Is the UK Net Zero Carbon Buildings Standard compulsory?
No. It is a voluntary industry standard. A pilot version was released in September 2024 and Version 1 was published on 10 March 2026, developed collaboratively by a group of built environment bodies including CIBSE, BRE, RIBA, RICS, IStructE and UKGBC. Because it is voluntary, describing a project as aligned with it is a claim that can be tested rather than a regulatory status.
Apex Insurance Brokers Limited is authorised and regulated by the Financial Conduct Authority (FRN 724952). This page is general information, not advice on a specific policy.