How is floor area measured on a commercial EPC?
Updated 23 October 2026 · SEO Dons Editorial
The floor area on a commercial EPC follows its own definition, which may not match the area in a lease or a valuation. It is recorded as an estimate, and several legal thresholds depend on it. The duties themselves are covered in do I need a commercial EPC? and in the guide to the display rule. This guide covers the measurement.
What is “total useful floor area”?
Regulation 2 of the 2012 Regulations defines it as “the gross floor area as measured in accordance with the guidance issued from time to time by the Royal Institution of Chartered Surveyors or by any body replacing that Institution”. The government’s guide to EPCs for non-dwellings describes the same measure in plainer words: the total area of all enclosed spaces, measured to the internal face of the external walls. It adds two conventions. Sloping surfaces such as staircases, galleries and tiered terraces are taken at their area on the plan, and areas that are not enclosed, such as open floors, covered ways and balconies, are excluded.
Two points follow. First, the regulation points to RICS guidance “from time to time”, so the convention can move when RICS updates it. RICS’s page on its Code of measuring practice says the 6th edition became globally effective in May 2015 and that a draft 7th edition is out for consultation. Until the 7th edition is published, it says, members should keep using the 6th edition and/or IPMS: All Buildings, and the basis of measurement used should be documented.
Second, the certificate carries an estimate. Regulation 9 requires an EPC to include “an estimate of the total useful floor area of the building”, and the guide says the assessor must validate plan data with a site inspection. The government’s separate DEC guide words the definition slightly differently, as gross floor area measured “in accordance with the Building Regulations”, so the regulation itself is the authority.
Which thresholds depend on the floor area?
Five lines are tied to floor area. Four are law today. The fifth is a proposal.
| Floor area | What it changes | Status | Source |
|---|---|---|---|
| Under 50 m² | A stand-alone building is outside the EPC duties in Part 2 of the 2012 Regulations | In force | Regulation 5(1)(g) |
| Over 250 m² | A building occupied in whole or part by a public authority and frequently visited by the public needs a Display Energy Certificate (DEC) and advisory report | In force | Government DEC guide |
| Over 500 m² | A building frequently visited by the public must display its valid EPC once one has been produced for a sale, letting or construction | In force | Regulation 10 |
| Over 1,000 m² | A public authority’s DEC is valid for 12 months instead of 10 years | In force | Regulation 14(4) |
| Over 1,000 m² | Privately rented buildings in England and Wales are proposed to reach EPC B from 2031, where cost effective | Proposal only; needs secondary legislation | Interim response, 18 June 2026 |
“Stand-alone” means entirely detached from any other building, so a small unit inside a larger block does not qualify for the 50 square metre rule. The DEC guide explains what each duty requires.
Why can the EPC area differ from the area in a lease or valuation?
Areas are measured for a purpose. The Valuation Office Agency (VOA), which values business premises for rates, usually measures offices using the net internal area (NIA) method and measures factories, warehouses and workshops using the gross internal area (GIA) method. Its business floorspace statistics also separate “the area used as the basis for valuation” from the total floor area of the property.
A lease or sale document may use another basis again. None of the official sources read for this guide gives a conversion between those measures and total useful floor area, so a rule of thumb would be a guess. If a decision turns on a few square metres, the answer is a measurement on the right basis, written down.
How does the energy model use the area?
The assessor builds the model from zones, and the total is what the zones add up to. The SBEM frequently asked questions give an example of an office inside a warehouse. A space above the office that is accessible, for instance by ladder, and usable, for instance for storage, is entered as its own zone. An unusable void above the office is not, and “will not be counted towards the useable floor area of the building”. Small unconditioned areas such as risers and store cupboards can be absorbed into the adjacent conditioned space, which adds their floor area to it.
The model uses the area to scale the result: the guide says the rating is adjusted for floor area, so it is independent of size for a given type of building. The FAQ says “useable” rather than “useful”, so read it as an illustration of how zones add up, not as a second definition.
What should you do if the building is close to a threshold?
- Read the area on the certificate and the date it was lodged. The government’s statistics notes warn that statistics drawn from certificates lodged before May 2009, when extra validation checks were introduced, may include anomalies that affect total useful floor area figures.
- Compare it with the areas in your plans, lease and rating records, and note which basis each one uses.
- If the answer changes which duty applies, ask the assessor how the figure was reached and which zone areas were entered.
- If the figure looks wrong, raise it with the assessor first and then with their accreditation scheme. What to do if your commercial EPC looks wrong sets out the steps.
- Keep the measurement record with the lease or sale file. How to read a commercial EPC shows where the area appears on the certificate.
Will the 1,000 square metre line for EPC B be measured the same way?
The government has not said. The interim response of 18 June 2026 states the proposal as “from 2031, it is proposed that all private rented buildings over 1,000 square metres in England and Wales will need to reach a higher standard of energy efficiency of EPC B, where cost effective”. It says buildings below 1,000 square metres are intended to stay at EPC E, and that the change takes effect only after secondary legislation has passed. Further detail on “implementation of the threshold” is promised in a forthcoming government response.
Until that response appears, saying which measure will apply would be a guess. What can be done now is to know each building’s total useful floor area and its lease area, and to keep both on file. EPC B by 2031 explains who the proposal would catch. If a building has no valid certificate, checking whether an EPC is needed is the starting point, and you can send an enquiry through this site’s form.
Sources
- Energy Performance of Buildings (England and Wales) Regulations 2012 (SI 2012/3118), regulations 2, 5, 9, 10 and 14, legislation.gov.uk (The National Archives), checked 22 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) (11 December 2017), checked 22 October 2026.
- A guide to display energy certificates and advisory reports for public buildings, Ministry of Housing, Communities and Local Government (GOV.UK) (10 August 2015), checked 22 October 2026.
- Minimum Energy Efficiency Standards (MEES) in the non-domestic Private Rented Sector: interim response, Department for Energy Security and Net Zero (GOV.UK) (18 June 2026), checked 22 October 2026.
- Code of Measuring Practice, Royal Institution of Chartered Surveyors (RICS), checked 22 October 2026.
- How offices are valued for business rates, GOV.UK, checked 22 October 2026.
- How factories, workshops and warehouses are valued for business rates, GOV.UK, checked 22 October 2026.
- Non-domestic rating: business floorspace, March 2025, background information, GOV.UK, checked 22 October 2026.
- NCM and SBEM frequently asked questions, uk-ncm.org.uk (BRE, official NCM and SBEM website), checked 22 October 2026.
- Energy Performance of Buildings Certificates in England and Wales: technical notes, Ministry of Housing, Communities and Local Government (GOV.UK) (30 July 2026), checked 22 October 2026.
Common questions
Is the floor area on my EPC measured or estimated?
The regulations require the certificate to include an estimate of the total useful floor area. The assessor must still validate the information, including any plan data, by making a site inspection, so ask which zone areas were entered if the figure matters.
Do balconies, covered walkways and open floors count?
No. The government guide excludes areas that are not enclosed, such as open floors, covered ways and balconies. Sloping surfaces such as staircases and galleries are counted at their area on the plan.
Does a mezzanine or storage deck count?
The SBEM FAQ gives one example: a space above an office that is accessible, for instance by ladder, and usable, for instance for storage, is entered as its own zone and counted. It is an example, not a rule for every mezzanine, so ask the assessor how yours was treated.