A specialist sustainability consultancy in the South West agreed to lead the operational energy strategy for a 35,000 square metre commercial office, targeting both BREEAM Outstanding and a NABERS UK 5-star design-for-performance rating. The modelling was diligent, the design team coordination was strong, and the building completed in 2023 with the design-stage NABERS UK certificate duly issued. Two years into operation, the developer — having marketed the building heavily on the strength of its net-zero credentials and let it on a long lease to an institutional tenant — found that the measured operational energy use was running roughly 80% above the modelled figure. The tenant invoked a clause in the lease tying rent reviews to operational performance. The developer’s solicitors wrote to the consultancy. The PI broker found that the policy responded in principle but that the limit was being eroded by defence costs faster than anyone had expected.
Performance-gap disputes of this shape are no longer unusual. As net-zero advisory work has matured from a peripheral service into a core revenue line for many M&E and sustainability practices, the claims profile of that work has begun to crystallise — and it is meaningfully different from the claims profile of traditional design work. This article looks at that exposure, the policy provisions that matter, and what we recommend to consultancies whose work increasingly sits at the operational-performance, low-carbon and certification end of the spectrum. It assumes familiarity with the wider PI framework set out in our pillar article on PI for building services consultants.
The shape of the advisory work
Sustainability and net-zero advisory work, as offered by UK building services consultancies in 2026, covers a wide range of services. Design-stage energy modelling — SAP for dwellings, SBEM for non-domestic, dynamic simulation in software such as IES-VE or TAS — sits at one end. Whole-life carbon assessment, including embodied carbon calculated under RICS or IStructE methodologies, is now common. Certification advisory work for BREEAM, LEED, WELL, Passivhaus and the design-for-performance and energy ratings under NABERS UK has become a discipline in itself. Specification and advice on low-carbon plant — heat pumps, heat networks, MVHR, on-site renewables — sits alongside the modelling work. And operational-performance services — post-occupancy evaluation, soft landings, in-use monitoring, performance verification — sit at the other end.
Each of these services has a claims profile of its own. Design-stage modelling tends to generate claims where measured performance diverges materially from modelled performance. Certification advisory work tends to generate claims where a target rating is missed, where a certificate is withdrawn or downgraded, or where the consultant’s advice on credits is challenged by the assessor. Embodied-carbon work tends to generate claims where reported figures are subsequently revised, where supply-chain data is shown to have been misrepresented, or where marketed claims are challenged by the ASA or CMA. Low-carbon specification claims look more like traditional M&E plant claims but with a particular tendency toward heat-pump under-sizing and noise complaints.
The regulatory and commercial backdrop
The advisory environment has changed substantially in recent years. The Minimum Energy Efficiency Standard for commercial property has driven sustained demand for energy assessment work, with the EPC threshold tightening and the prospect of further tightening continuing to shape lender and investor decisions. The Future Buildings Standard and Future Homes Standard, even where final implementation dates have moved, have already shaped the design conversation around heat pumps, ventilation and operational energy. The CRREM transition risk pathway and similar tools have made operational energy and carbon a matter of asset valuation rather than just compliance.
NABERS UK, launched in 2020 as the UK adaptation of the Australian NABERS scheme, has become a meaningful part of the commercial office market for new build and major refurbishment. The design-for-performance pathway in particular requires consultants to commit to a modelled rating that will be verified in operation, which exposes the modelling consultant to performance-gap claims in a more direct way than older certification regimes.
On the marketing side, the Advertising Standards Authority published updated guidance on environmental claims and the Competition and Markets Authority’s Green Claims Code sets out expectations for substantiation of environmental marketing. Where a developer markets a building as “net zero” or “carbon neutral” on the strength of advice from a sustainability consultant, and the marketing claim is subsequently challenged, the consultant who provided the underlying figures may be drawn into the response. The ASA has been increasingly willing to investigate property and infrastructure claims, and CMA enforcement in adjacent sectors has set expectations that will increasingly bear on the built environment.
Performance-gap claims: the central exposure
The performance gap — the difference between modelled energy performance at design stage and measured energy performance in operation — has been a known phenomenon in the UK industry for at least two decades. What is new is the willingness of clients, tenants and investors to monetise it. A building marketed and valued on its design-stage energy credentials, but performing materially worse in use, may now generate claims for rent abatement, void losses, remediation costs, lost certification value and reputational damage.
The defensibility of a performance-gap claim against the modelling consultant typically turns on several factors. First, the modelling assumptions — were operating hours, occupancy densities, equipment loads and weather files used appropriately, and were the assumptions documented? Second, the chain of design decisions — were variations made by the contractor or by other consultants that affected the building’s energy performance, and were those variations flagged? Third, the operation of the building — is the building being used in ways that depart materially from the modelling assumptions? Fourth, the caveats in the original report — did the consultant make clear, in language an informed lay reader would understand, the limits of what design-stage modelling can predict about in-use performance?
A well-defended performance-gap claim is often defensible. A poorly documented one often is not. The practical implication for the consultancy is that report drafting, assumption logging and version control matter more than they used to.
NABERS UK, MEES and the certification claims environment
NABERS UK design-for-performance work warrants particular attention. The consultant commits, at design stage, to a rating that will be verified after twelve months of operation. If the verified rating is lower than the committed rating, the consequences may be contractual (failure to achieve a warranted level of performance), commercial (the building’s marketing and valuation having been built on the higher rating), or both. The PI policy’s response to such claims depends on whether the consultant’s advisory services are within scope and whether the relevant clauses of the consultant’s appointment cap or define the liability.
MEES-related work has generated a steady stream of claims around EPC ratings and the advisory work that supports them — assumptions used in the SAP or SBEM model, the choice of methodology, the treatment of renewable contributions, the implications for landlord lettings. These claims are typically smaller in value than performance-gap claims but more frequent.
BREEAM, LEED, WELL and Passivhaus certification advisory work generates a different kind of claim: where a target rating is not achieved, where a certificate is withdrawn after issue, or where the consultant’s advice on individual credits is subsequently challenged. The PI defence often turns on whether the consultant was engaged to advise (in which case the standard of care is reasonable skill and care) or to deliver a certificate (in which case the consultant has effectively warranted an outcome). Appointment letters are not always as clear on this distinction as they should be.
Embodied carbon, supply chain and greenwashing
Embodied-carbon advisory work has grown rapidly since the introduction of RICS’s Whole Life Carbon Assessment for the Built Environment professional statement and the parallel rise in lender and investor interest in net-zero pathways. The work typically involves a calculation of embodied carbon across the building’s life cycle, drawing on environmental product declarations and database figures for material carbon intensities.
The claims exposure has two main components. First, the technical: where the calculation methodology is challenged, where the data sources are shown to be unreliable, or where the assumptions about end-of-life and circular economy benefits are disputed. Second, the marketing: where the consultant’s figures are used in marketing material making “net zero” or “low carbon” claims, and the marketing is subsequently challenged by the ASA, the CMA, a competitor or an activist organisation.
The marketing exposure is harder to predict and to limit. Where a consultancy’s figures are quoted in marketing without the consultant’s name, the consultant may nevertheless be drawn into the response if the developer points to its advice as the basis for the claim. Hedged language in the original report — clear caveats about scope, methodology and uncertainty — is the primary defence.
Heat pumps, low-carbon systems and specification disputes
The push toward electrification of heat has generated a class of specification disputes that did not exist five years ago. Heat-pump sizing for retrofit residential schemes has been particularly difficult: domestic heat-loss surveys are often based on limited information, occupant behaviour varies widely, and the move from a gas boiler with substantial peak capacity to a heat pump sized to design heat-loss conditions can produce comfort issues that occupants experience as system failure.
In the non-domestic sector, large heat-network and ambient-loop schemes have generated disputes around overall system performance, individual building-level performance, metering accuracy and billing. The consultant’s exposure depends heavily on the scope of services — whether it was engaged for full system design, for performance specification only, or for advisory input — and on the clarity of the assumptions and limitations in the design documentation.
PI cover for this work is generally available but the underwriting questions are increasingly granular. Underwriters want to understand the consultancy’s approach to heat-pump sizing, its post-installation performance verification protocols, and its arrangements for handling complaints.
Policy implications and what to look for
For a sustainability or net-zero advisory consultancy, several policy provisions warrant particular attention beyond the standard PI considerations covered in the pillar article.
Scope of insured services. The schedule should explicitly cover the advisory services the firm offers. Some older PI wordings define insured services in terms of traditional M&E design and do not clearly capture sustainability advisory, certification work, embodied-carbon assessment or performance verification. Where the firm’s revenue is shifting toward these services, the wording should be updated.
Defence costs and aggregation. Performance-gap claims are typically expert-heavy and protracted. Defence-costs-outside-the-limit wordings, where available, are valuable. Aggregation language matters: a performance-gap claim by a building owner, by tenants and by a funder on the same scheme may aggregate or may not, depending on the wording.
Greenwashing and marketed claims. Most standard PI wordings do not specifically exclude or specifically cover claims arising from the use of the consultant’s work in marketing material. The position is typically arguable on the wording. Where the consultancy is regularly providing input that will be used in marketing, the exposure should be raised with the underwriter at proposal stage.
Certification outcomes. Where the consultancy’s appointment commits to achieving a specified certification rating, the PI policy’s response may depend on whether the obligation is interpreted as a warranty or as an obligation of reasonable skill and care. Appointment review is essential.
Run-off considerations. Performance-gap and operational-performance claims can emerge years after completion, as data accumulates and as buildings change hands. Run-off planning for advisory work needs to take account of this latency, although the limitation periods are generally those of standard contract and tort rather than the extended Defective Premises Act windows discussed in our Building Safety Act cluster article.
How Apex approaches sustainability advisory PI
We work with a number of UK consultancies whose revenue mix has shifted materially toward sustainability and net-zero advisory work over the last five years. Our approach to placement focuses on three areas.
First, getting the scope right. We work with the firm to articulate the full range of advisory services in language that matches how underwriters describe the work, and we negotiate amendments to wordings where the standard schedule does not capture what the firm actually does.
Second, market selection. Not every PI insurer that writes construction professionals is comfortable with sustainability advisory work; some markets have specific appetite for it, others approach it warily. The choice of insurer matters more on this work than on traditional design.
Third, appointment review. We routinely review the firm’s standard appointment letters, NDA templates and certification advisory contracts against the PI cover, flagging clauses that create exposure outside the policy’s response — particularly outcome-based obligations on certification ratings, warranties on operational performance, and indemnities relating to marketing claims.
Where claims arise, we act as the consultancy’s advocate. Performance-gap claims in particular often turn on the early framing of the dispute, and a broker-led notification that sets out the firm’s position clearly can shape the way the insurer approaches the matter.
Frequently asked questions
What is a performance gap and why is it a PI issue? The performance gap is the difference between modelled energy performance at design stage and measured performance in operation. It is a PI issue because clients, tenants and investors increasingly bring claims against the modelling consultancy where in-use performance falls materially short of design figures. Defensibility usually depends on assumption logging, design coordination, building operation and the caveats in the original report.
Does a standard PI policy cover NABERS UK design-for-performance work? Most construction-professional PI wordings will cover NABERS UK advisory work provided the insured services on the schedule are drafted broadly enough. Where the appointment commits to a specific rating, the contractual commitment and the policy response should be reviewed together.
Am I exposed if a developer markets a building as “net zero” on the strength of my carbon assessment? Potentially. If the marketing claim is challenged and the developer points to the consultant’s work as the basis, the consultant may be drawn into the response. The defensibility depends on the clarity, scope and caveats of the original report.
What is the Green Claims Code and does it affect sustainability consultants? It is CMA guidance on substantiation of environmental claims in marketing. Although directed at the businesses making claims, it shapes the standard against which marketed claims are judged and indirectly affects the standard of care expected of supporting consultants.
How are heat-pump specification disputes typically resolved? It depends on the scope of services and the facts. Disputes typically focus on heat-loss assumptions, system selection, the interface with the installer and the documentation of advice. Early PI insurer engagement is usually advisable.
Can I limit my liability for performance-gap claims contractually? Liability caps, exclusions and net-contribution clauses can all play a role, subject to enforceability. Standard form appointments include relevant clauses, but advisory work often requires bespoke drafting joined up with the PI placement.
Should sustainability advisory work be insured under the same policy as M&E design? In most cases yes, provided the schedule captures the advisory services. A single PI placement with a comprehensive insured-services definition is generally simpler and more cost-effective than separate placements.
Related guides
For the wider professional indemnity framework, see our pillar article on PI for building services consultants. For the Building Safety Act dimension — particularly relevant where advisory work touches HRBs — see our cluster on M&E design risk under the Building Safety Act.
About this guide. This article was prepared by Apex Insurance Brokers and last reviewed in May 2026. It is intended as general information for UK sustainability and net-zero advisory practices and is not advice on any specific contract, policy or claim. Market conditions and regulatory expectations continue to evolve; readers should take advice on their own circumstances.
Apex Insurance Brokers. Authorised and regulated by the Financial Conduct Authority, Firm Reference Number 724952. Registered in England and Wales, Companies House number 07014570. Registered office: Bristol. Email: info@apexinsurancebrokers.co.uk. Telephone: 0117 325 0027.
This article is part of our PI insurance for building services consultants (pillar guide). See the pillar for the full guide.