How commercial EPC ratings are worked out
Updated 19 October 2026 · SEO Dons Editorial
A commercial EPC rating is an asset rating. Approved software models the carbon emissions from the building's fabric and fixed services under a standardised pattern of use, compares the result with a reference building of the same size, shape and use, and converts it into a score and a band from A+ to G. Because the use is standardised, your opening hours, thermostat habits and energy bills play no part in it.
What does a commercial EPC rating actually measure?
The Energy Performance of Buildings (England and Wales) Regulations 2012 define an asset rating as an energy performance indicator worked out from the amount of energy estimated to meet the different needs of a standardised use of the building. Every EPC entered on the register since 9 January 2013 must show that asset rating, calculated using the method approved by the Secretary of State, and must include a reference value so the result can be compared.
The government's guide to EPCs for non-dwellings explains that the rating is based on the building itself (the fabric) and its services, such as heating, ventilation and lighting. In practice the calculation draws on four groups of information:
- the construction: walls, roofs, floors and glazing
- the zones of the building, what each one is used for and its occupancy profile
- the heating, cooling, ventilation and hot water systems
- the lighting
The result is expressed as a carbon dioxide based index. It is adjusted for the building's total useful floor area, so that size alone does not decide the outcome for a given type of building. The register's certificate pages put it in one line: the better the rating and score, the lower the property's carbon emissions are likely to be.
What is the reference building, and why does it matter?
The score is relative, not absolute. The government guide says the calculation compares the carbon emissions of the building with those of a reference building: an equivalent building of the same size, shape and use, built to a notional specification. The official National Calculation Methodology (NCM) website describes the same principle for Building Regulations checks, where a building's annual energy use is compared with a comparable notional building, and notes that a similar process produces the asset rating for EPCs.
This is why a large distribution warehouse and a small shop can land in the same band. Each one is judged against a benchmark version of itself, so the rating shows how well its fabric and services perform for that size, shape and activity, not how much energy it uses in total.
The register also gives some context under the headline band. In a section headed "How this property compares to others", it shows the ratings that similar properties could have if newly built and if typical of the existing stock. That is a quick way to see whether your building is behind, level with or ahead of the typical stock for its type.
How do the A+ to G bands work?
Each certificate shows a band and a numeric score, and on a commercial EPC a lower score is better. The register sets the bands out like this:
| Band | Score |
|---|---|
| A+ | Below zero |
| A | 0 to 25 |
| B | 26 to 50 |
| C | 51 to 75 |
| D | 76 to 100 |
| E | 101 to 125 |
| F | 126 to 150 |
| G | Over 150 |
Band E is the line that matters most to landlords. Since 1 April 2018, landlords of non-domestic property in England and Wales have only been able to grant, extend or renew a tenancy if the property has at least an EPC E, unless they have registered a valid exemption. From 1 April 2023 the same minimum applies to all privately rented non-domestic property, including lettings that simply continue. Commercial certificate pages on the register state that properties can be let if they have an energy rating from A+ to E.
Below the band, the certificate breaks the result down: the main heating fuel, the building environment (for example heating with natural ventilation, or air conditioning), the assessment level, the building emission rate and the primary energy use per square metre. The register describes primary energy use as a measure of the energy required for lighting, heating and hot water. These lines are worth reading, because they show what the model assumed about your building.
Which software works out the rating: SBEM or DSM?
Only government-approved software may be used to produce a commercial EPC. The current notice of approval, which took effect on 24 March 2026, says the energy performance of a building that is not a dwelling must be calculated using an approved implementation of the NCM, meaning SBEM or an approved dynamic simulation model (DSM). It approves the 2026 version of the NCM for non-dwellings in England and the 2022 version for existing non-dwellings in Wales. SBEM, the Simplified Building Energy Model, estimates monthly energy use and carbon dioxide emissions under standardised operating conditions from a description of the building's geometry, construction and building services, while approved DSM tools are the alternative where, for example, a building's systems are not among SBEM's options. Which route your building needs, and the assessor level that goes with it, is explained in SBEM Level 3 vs Level 4 vs DSM.
Why doesn't the way you run the building change the rating?
Because the rating is built on a standardised use. The assessor divides the building into zones and gives each one an activity, such as office, retail, storage or kitchen, and the software applies that activity's standard assumptions. The government guide notes that different activities bring different periods of occupancy, different required temperatures and different needs for lighting and hot water. The NCM website adds that the parameters and schedules for each activity are standardised so buildings can be compared consistently, and that users cannot change them for energy certification.
Take a hypothetical pair of identical units with the same fabric, heating and lighting. One trades around the clock and the other opens nine to five. Their energy bills will differ, but their EPCs will not. Turning the thermostat down, running a switch-off campaign or moving to a cheaper tariff does not move the score either.
What does move it is a change the model records: insulation, glazing, a different heating system or fuel, better controls, more efficient lighting, or a change in what the zones are used for. Even then, nothing happens to the published rating until a new EPC is lodged. Under the 2012 Regulations an EPC stays valid until it is more than 10 years old or a newer EPC for the building is entered on the register.
How is a DEC operational rating different?
A Display Energy Certificate (DEC) works the other way round. The regulations define an operational rating as an indicator based on the energy actually consumed while a building is occupied over a period of time. The government's DEC guide says a DEC shows a building's energy performance based on actual consumption recorded over the last 12 months, and that typical performance for the building type equals an operational rating of 100. DECs are required for buildings over 250 square metres that are occupied by a public authority and frequently visited by the public. Private organisations do not need one but can display one voluntarily. There is more on this in Display Energy Certificates explained.
| Commercial EPC (asset rating) | DEC (operational rating) | |
|---|---|---|
| What it measures | Modelled emissions from the fabric and fixed services under standardised use | Actual metered energy use over 12 months |
| Effect of how the building is run | None | Directly reflected |
| Scale | A+ to G, lower score is better | A to G, typical building scores 100 |
| When it is needed | Construction, sale, letting and some modifications that create or merge separately used parts | Public authority buildings over 250 square metres frequently visited by the public |
| Comes with | A recommendation report | An advisory report |
Because one is modelled and the other is measured, the two can tell different stories about the same building. A well-specified building that is run wastefully can hold a good EPC and a poor DEC, and a modest building run with care can show the reverse.
What should you do with your rating?
Start with the detail behind the band. Check that the floor area, heating fuel, building environment and assessment level match the building, then read the recommendation report that comes with the certificate, which lists the improvements the assessment identified and how quickly each might pay back. How to read a commercial EPC recommendation report walks through it section by section.
If the building has no EPC, the current one is close to 10 years old, or works since the last assessment should change the result, a new assessment by an accredited non-domestic energy assessor is the only way to update the rating. You can request quotes for a commercial EPC through this site's form, and the enquiry is passed to companies that carry out assessments.
Sources
- The Energy Performance of Buildings (England and Wales) Regulations 2012, regulation 2, legislation.gov.uk, checked 19 October 2026.
- The Energy Performance of Buildings (England and Wales) Regulations 2012, regulation 9, legislation.gov.uk, checked 19 October 2026.
- A guide to Energy Performance Certificates for the construction, sale and let of non-dwellings, Ministry of Housing, Communities and Local Government (GOV.UK), checked 19 October 2026.
- UK's National Calculation Method for Non Domestic Buildings (NCM and SBEM introduction), uk-ncm.org.uk (BRE, official NCM and SBEM website), checked 19 October 2026.
- NCM and SBEM frequently asked questions, uk-ncm.org.uk (BRE, official NCM and SBEM website), checked 19 October 2026.
- Methodologies for expressing the energy performance of buildings in England and Wales: notice of approval, Ministry of Housing, Communities and Local Government (GOV.UK), checked 19 October 2026.
- Find an energy certificate, GOV.UK register (search page, plus the standard wording shown on non-domestic EPC and recommendation report pages), checked 19 October 2026.
- Non-domestic private rented property: minimum energy efficiency standard - landlord guidance, Department for Energy Security and Net Zero (GOV.UK), checked 19 October 2026.
- A guide to display energy certificates and advisory reports for public buildings, Ministry of Housing, Communities and Local Government (GOV.UK), checked 19 October 2026.
- Energy Performance Certificates for your business premises, GOV.UK, checked 19 October 2026.
Common questions
Will lower energy bills improve my commercial EPC rating?
No. A commercial EPC is an asset rating based on a standardised use of the building, so actual consumption and tariffs are not inputs. Bills and the rating only move together when the change behind them, such as more efficient lighting or heating, is recorded in a new EPC.
Is a higher score better or worse on a commercial EPC?
Worse. On the commercial scale a lower score is better: A+ is below zero, A runs from 0 to 25 and G is anything over 150. Band E, the minimum for most non-domestic lettings in England and Wales, covers scores of 101 to 125.
Why can two similar units in one building have different ratings?
Each EPC reflects the fabric, services, lighting and zone activities recorded for the part that was assessed, so differences in heating, controls, glazing, lighting or use can produce different scores. Where a non-residential block has a common heating system, the regulations also allow certification based on the whole building.
Does my EPC change when the government updates the calculation method?
No. A lodged EPC stays valid for up to 10 years unless a newer EPC for the building is lodged. A new assessment is calculated with the methodology approved at the time, currently set by the notice of approval that took effect on 24 March 2026.