How to prepare your building for a commercial EPC assessment

Updated 19 October 2026 · SEO Dons Editorial

What documents should you gather?

Start with floor plans. Government guidance says the zones of a building and their dimensions can often be taken from plans, and that up-to-date information and plans make the assessment less time-consuming. Without plans, the assessor has to measure everything on site.

Then pull together anything that describes the building services and fabric. The non-domestic EPC conventions, which accredited assessors must follow, list the kinds of documents they can rely on. Useful items include:

floor plans and, for newer or altered buildings, "as built" drawings
operation and maintenance manuals and the building logbook
manufacturers' technical data sheets for boilers, heat pumps, air conditioning and ventilation units
commissioning records, including any air permeability or ductwork leakage test certificates
service and maintenance records, installation records and building control sign-off sheets
the lighting specification, if the lighting has been replaced
the number of any previous EPC, and the planning use class if you know it

Documents only count if they match what is on site. The conventions say there must be a demonstrable link between what the assessor sees and the paperwork. Their example is a boiler: the model number read from the unit on site can be matched to the manufacturer's data sheet to confirm its efficiency. For newer buildings, design-stage documents alone are not acceptable, so make sure drawings and specifications are the "as built" versions.

Which areas will the assessor need to reach?

Every part of the building that is being assessed. The assessor has to understand the internal layout and what each space is used for, and must validate zone dimensions, insulation and building services through plans, a physical survey or both. Even where detailed plans exist, the information has to be checked with a site inspection.

Plant needs particular attention. The conventions say assessors should make every effort to gain access to heating and cooling generators, and where details cannot be confirmed, the assessor works on a worst-case basis for the equipment believed to be present. Before the visit, it helps to:

find keys for plant rooms, risers, cupboards and roof access
tell tenants the date and which areas will be entered
arrange for someone who knows the building to be available
clear routes to boilers, air conditioning units and ventilation plant

Occupied buildings are covered by the law. Regulation 45 says everyone with an interest in, or in occupation of, the building must give the appointed energy assessor the access reasonably necessary to inspect it.

What happens on the day of the visit?

Government guidance describes three main steps once an assessor is commissioned: gathering information about the building, analysing it and identifying the different zones, and entering it into approved software, which for commercial buildings is either the Simplified Building Energy Model (SBEM) or a dynamic simulation model (DSM).

On site, that usually means the assessor:

measures or checks the floor areas and dimensions of each zone
records what each area is used for, such as office, retail, kitchen or storage
inspects the heating, ventilation and air conditioning, including controls, metering and fuel
records the lighting and its controls in each zone
notes the construction of the roof, floors, walls and glazing

If you have the building's authorised planning use class, give it to the assessor. The conventions say it will be used as the building type if it comes from a suitable source; otherwise the type is based on what the assessor sees on the day.

An EPC visit is not a safety or servicing check. Government guidance says the EPC assesses the operational efficiency of the systems but will not comment on their safety or maintenance, or confirm that they are fit for purpose.

For larger or more complex buildings (levels four and five), assistants may help gather data, but the accredited assessor must still visit and inspect the building and verify the data before the EPC is lodged.

Can preparation affect the rating?

It can stop the rating being based on assumptions. The conventions tell assessors to use the software's default values only where there is no more specific information, and say defaults should be avoided where possible. Combined with the worst-case rule for unconfirmed heating and cooling equipment, missing paperwork can lead to a less favourable result than the building deserves.

A few specific cases are worth knowing about:

Air tightness. The conventions only allow the lowest air permeability values to be entered with an accredited air pressure test result, so have any test certificate to hand.
Decommissioned systems. A heating or cooling system that has been decommissioned is left out of the assessment if there is robust evidence, such as a decommissioning certificate or an invoice for the work.
Condemned systems. A system that has only been condemned must still be included, because it could be made operational again.

What happens after the visit?

The assessor enters the data into approved software, which produces the EPC and a recommendation report. The EPC is then lodged on the central register, which generates the certificate reference number every valid EPC must carry, and a copy goes to the person who commissioned it.

Recommendations are grouped into four categories: short-term payback (under 3 years), medium-term (3 to 7 years), long-term (over 7 years) and other recommendations. The guide to the recommendation report explains how to read them.

The EPC regulations do not require you to carry out the recommendations. Lettings are different: GOV.UK says that from 1 April 2023 privately rented non-domestic property must have at least an EPC E rating unless a valid exemption is registered, even where the tenancy has not changed. If the result is F or G and the building is let, see the MEES compliance page.

How long does the certificate last?

GOV.UK says all EPCs are valid for 10 years. Under regulation 9, an EPC is valid if it was entered on the register no more than 10 years before it is made available and no newer EPC has been lodged for the building since. Within that period it can be reused for further sales and lettings.

If the building is over 500 square metres, frequently visited by the public and already has an EPC from a sale, letting or construction, GOV.UK says the certificate must be displayed. A new EPC can be needed sooner if the building is changed so it has more or fewer separate parts and the work includes providing or extending heating, air conditioning or mechanical ventilation.

When the building is ready, you can request quotes through the commercial EPC quote form, and the checklist in what you need to get a commercial EPC quote shows what to include.

Sources

A guide to Energy Performance Certificates for the construction, sale and let of non-dwellings, Ministry of Housing, Communities and Local Government (GOV.UK), updated 11 December 2017, checked 19 October 2026
Non Domestic EPC Conventions for England and Wales, Issue 9, Non-Domestic EPC Conventions Group (published on the National Calculation Methodology website), checked 19 October 2026
Energy Performance Certificates for your business premises, 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
Regulation 45: duty to cooperate, legislation.gov.uk, checked 19 October 2026
Non-domestic private rented property: minimum energy efficiency standard - landlord guidance, Department for Energy Security and Net Zero (GOV.UK), last updated 5 May 2026, checked 19 October 2026

Common questions

Do I need to be at the building during the assessment?

Not necessarily, but someone has to give the assessor access to every area, including plant rooms and tenants' space. It helps if that person knows where the heating, cooling and ventilation equipment is and can answer questions about how the building is used.

Will the assessor check whether the boiler is safe?

No. Government guidance says the EPC assesses the operational efficiency of the building services but will not comment on their safety or maintenance, or confirm that they are fit for purpose. Safety checks are a separate matter for a qualified engineer.

What if part of the building is empty or unfitted?

The assessor still needs access to it. For a shell and core building, government guidance says the EPC is based on the most energy-intensive fit-out allowed by Part L, so tell the assessor in advance which areas have no services installed.

Do I have to carry out the recommendations in the report?

Not under the EPC regulations, which place no statutory requirement on owners to carry them out. If the building is let and rated F or G, the minimum energy efficiency standard may require improvements or a registered exemption.