ESOS energy audit — the 95% rule
An ESOS energy audit is the default route to compliance, and it is defined by one number.
The audit must cover at least 95% of your total UK energy consumption, across buildings, transport and industrial processes.
No more than 5% may be set aside as de minimis.
Everything else — the twelve-month reference period, the site visits, the lead assessor sign-off — follows from getting that coverage right.
It is an audit in the energy sense, not the accounting sense
An ESOS energy audit is not a financial audit and not an assurance engagement.
Nobody gives an opinion on your figures.
What happens is that a registered assessor examines how your organisation uses energy, identifies cost-effective savings opportunities, and signs to confirm the assessment meets the scheme’s requirements.
That distinction matters because it changes what “passing” means: the scheme asks you to look properly and record what you found, not to hit a performance threshold.
The 95% rule, on your numbers
Enter your total annual UK energy consumption.
The split below is the coverage you must audit and the de minimis you may exclude.
The threshold used to be 90%, which allowed a 10% exclusion; the 2023 amendment regulations raised it.
Twelve consecutive months, containing one fixed date
Phase 4 constrains the reference period at both ends.
It must include the qualification date of 31 December 2026, and it must close before the compliance deadline of 5 December 2027.
Pick a start month and the validator will tell you whether the window works.
What an ESOS energy audit has to cover
Three domains, one total, and a depth requirement inside it.
Audit, ISO 50001, or a mix
The energy audit is the default, not the only, route to the 95%.
And two routes that worked in earlier phases no longer do.
The sign-off chain
An audit nobody signs is not compliance.
Four steps close the loop, and two of them are personal accountability rather than paperwork.
What is left before 5 December 2027
Two dates govern Phase 4, and the earlier one is the one people forget.
What ESOS energy audits cover
ESOS energy audits must cover at least 95% of total UK energy consumption across all business activities, including buildings, industrial processes and transport (GOV.UK).
The 95% figure is not the original one: the ESOS (Amendment) Regulations 2023 raised coverage from 90%, cutting the de minimis exclusion from 10% to 5% (SI 2023/1182).
Within that 95%, the audit must go further on areas of significant energy consumption, and site visits are required where consumption is significant.
The practical consequence is that coverage and depth are two separate tests: a thin audit spread across 95% of your estate does not satisfy the scheme.
Energy is converted to a common basis using the annual DESNZ conversion factors.
For the qualification test that gets you here in the first place, see ESOS requirements and the exemptions.
Data requirements and the reference period
ESOS energy audits must be based on twelve months of verifiable energy consumption data.
For Phase 4 that twelve-month reference period must include the qualification date of 31 December 2026 and end before the compliance deadline of 5 December 2027 (GOV.UK).
The earliest a compliant period could begin is 1 January 2026 and the latest it could end is 4 December 2027.
Total energy consumption and significant energy consumption may use different twelve-month periods, which is useful where sub-metering came online part way through.
Acceptable sources include energy bills, meter readings and consumption-monitoring systems, provided each is capable of independent verification.
Estimates are permitted where data genuinely does not exist, but the basis has to be stated in the audit rather than left implicit.
Records should be retained for possible Environment Agency inspection.
Standards that apply to ESOS energy audits
ESOS does not mandate a single audit methodology, but it does require audits to meet a recognised standard.
In practice that means ISO 50002 or the EN 16247 series, which set out how an energy audit should be planned, conducted, and reported.
Both require a systematic approach: an agreed scope, a data-collection phase, analysis of consumption patterns, identification of opportunities, and a report that a reader can follow from data to recommendation.
Lead assessors are drawn from approved registers and must meet competence requirements — see ESOS lead assessor requirements for the registers and the PAS 51215 framing.
Whether the audit is run in-house or bought in is a separate question from who signs it off; choosing an ESOS consultant covers what a compliant engagement has to produce and what to ask before appointing one.
Where an organisation holds ISO 50001 certification accredited by UKAS and covering the organisation’s total energy consumption — or its significant energy consumption, the areas comprising at least 95% of the total — the participant is deemed to have complied with the duties to appoint a lead assessor, carry out an ESOS energy audit and produce an ESOS report. It does not have to reach 100%, and a notification of compliance is still required.
What ESOS audit reports must include
The audit report is the evidence that the assessment happened properly, so its contents matter as much as its conclusions.
It should record total energy consumption for the reference period and how that figure was arrived at.
It should identify the areas of significant energy consumption and explain how they were selected.
It should set out the cost-effective energy-saving opportunities identified, with enough detail that a reader can understand the basis of each.
It should state the methodology followed, the data sources used, and any estimation or apportionment applied.
And it should record the site visits undertaken.
Structures for the pack itself are on ESOS templates, and the plan that follows from it on the ESOS action plan.
What is actually submitted to the Environment Agency — as opposed to what stays in your own records — is set out on ESOS reporting and notification.
How ESOS audits differ from other energy assessments
An ESOS energy audit is a scheme-specific exercise, and several adjacent things are commonly mistaken for it.
A Display Energy Certificate rates a building’s operational energy use; it was a valid ESOS route in earlier phases and was removed for Phase 4 by regulation 26 of SI 2026/701.
An ISO 50001 energy management system is an ongoing management framework rather than a four-yearly assessment, and it substitutes for the audit where certification covers total or significant (at least 95%) energy consumption.
A SECR disclosure reports energy and emissions annually in the directors’ report; it is a disclosure obligation, not an audit, and it neither satisfies ESOS nor is satisfied by it — see the SECR guide.
Sustainability assurance under ISSA (UK) 5000 is an opinion on reported information, which is a different exercise again — see sustainability assurance.
Where ESOS data can be reused for UK SRS and SECR reporting, the overlap is mapped in ESOS and UK SRS integration.
The standards that reporting runs on are a separate subject again — see UK SRS S1 and S2 explained.
ESOS energy audit — frequently asked questions
ESOS energy audits must be based on 12 months of verifiable energy consumption data covering at least 95% of total consumption. For Phase 4 the reference period must include the qualification date of 31 December 2026 and end before the 5 December 2027 compliance deadline, so the earliest start is 1 January 2026 and the latest end is 4 December 2027. Data sources include energy bills, meter readings and consumption monitoring systems, all of which must be capable of independent verification. Total energy consumption and significant energy consumption may use different 12-month periods.
Yes, site visits are mandatory for areas of significant energy consumption. Coverage and depth are separate requirements: reaching 95% coverage across the estate does not remove the obligation to examine significant consumption in detail, and a lead assessor will expect to see which sites were visited and why those were selected.
ESOS does not mandate one methodology but requires audits to meet a recognised standard, in practice ISO 50002 or the EN 16247 series. Both require a systematic approach covering scope, data collection, analysis, identification of opportunities and reporting. Lead assessors must come from an approved register and meet competence requirements.
An ESOS audit is a four-yearly, scheme-specific assessment with statutory sign-off. Display Energy Certificates and Green Deal Assessments were valid routes in Phases 1 to 3 but were removed for Phase 4 by regulation 26 of SI 2026/701, which omits regulation 34 of the 2014 Regulations. ISO 50001 is an ongoing management system that substitutes for ESOS audits where UKAS-accredited certification covers total energy consumption, or significant energy consumption — at least 95% of the total; it does not have to reach 100%. SECR is an annual disclosure obligation rather than an audit, and satisfying one does not satisfy the other.
Total energy consumption for the reference period and how it was calculated; the areas of significant energy consumption and how they were identified; the cost-effective energy-saving opportunities found, with the basis for each; the methodology and data sources used, including any estimation or apportionment; and a record of site visits. Documentation must be retained for potential Environment Agency inspection and should demonstrate a systematic approach to energy-efficiency planning.
Not if the UKAS-accredited certification covers your total UK energy consumption, or your significant energy consumption (at least 95% of the total), and is valid on 5 December 2027 — in that case ISO 50001 is a complete compliance route and lead assessor sign-off is not required either. Certification does not have to reach 100%. Notification to the Environment Agency is still required. Where certification covers only part of the estate, a mixed approach is permitted provided audits and certification together reach the 95% coverage requirement.
Non-compliance is dealt with by civil sanctions rather than criminal prosecution. The Environment Agency may impose penalties of up to £50,000 plus £500 a day for failing to carry out an ESOS assessment, and up to £5,000 plus £500 a day for failing to notify. Non-compliance can also be published. Penalties are enforcement outcomes, not fees. The ESOS penalties guide sets out the civil-penalty table by breach type and the Environment Agency’s stepped methodology for arriving at a figure.
Primary sources
Every figure, date and obligation on this page is cited to one of these.
Across the ESOS guidance set
ESOS explained
What the Energy Savings Opportunity Scheme is, who runs it, and how the phases work.
RequirementsESOS requirements
The compliance steps from qualification to notification.
AssessorsLead assessor requirements
Approved registers, competence, and what the assessor signs.
NotificationNotification and MESOS
Submitting compliance through the Environment Agency’s service.
After the auditESOS action plan
The Part 6A plan and the annual progress updates that follow.
Phase 4Phase 4 compliance guide
The whole phase in one place, end to end.
Also: all ESOS deadlines · exemptions · templates · the legislation · compliance overview · reusing ESOS data for UK SRS.
Check the 95%, or read the whole scheme
Neither sends anything anywhere.