# What happens in a non-domestic EPC assessment > What an assessor actually does, why the evidence you can produce changes the rating legitimately, and how to prepare for an assessment. Source: https://commercialepcupgrades.co.uk/non-domestic-epc-assessment --- # What happens in a non-domestic EPC assessment A non-domestic EPC is not a measurement. It is an asset rating of the building and its services, not of your metered use: an assessor collects data about the building and its fixed services, enters it into approved modelling software, and the software produces the rating. That has a consequence most landlords never hear, which is that what you can prove about your building changes your rating. General guidance, not legal advice Energy performance rules for commercial property in England and Wales have changed repeatedly, and proposals have moved during consultation. This page describes the position as we understand it and is written to be useful rather than definitive. Check the current position and your own obligations with a solicitor or a qualified assessor before committing to capital spend. ## Where defaults come from, and why they hurt When the assessor cannot establish something, the methodology does not let them guess optimistically. It requires a default, and defaults are deliberately cautious, because the alternative would be a system that rewards vagueness. So a building with excellent insulation that nobody can evidence is modelled as though it has the minimum. A boiler with a good efficiency figure that nobody can produce documentation for is modelled at a conservative assumption. The building is better than its certificate, and the gap is pure paperwork. This is the single most useful thing on this page: finding the documentation is free, and it is sometimes worth a band. ## What to have ready - Construction drawings and specifications, particularly anything showing insulation types and thicknesses. - Building control or completion documentation from any extension, refurbishment or fit-out. - Manufacturer data and commissioning certificates for boilers, chillers, air handling units and controls. - Lighting schedules: fitting types, wattages and the control strategy, by zone. - Any previous EPC and its recommendation report, which tells the assessor what was there before. - Evidence of anything installed since the last assessment, which is frequently the thing nobody mentions. ## What the assessor is doing on site Measuring and zoning the building, identifying the construction of each element, recording the fixed services and their controls, and photographing evidence. They are not testing performance, and they are not there to advise you on what to fix. Access matters. Plant rooms, roof voids, risers and locked areas that cannot be inspected become defaults, with the consequences described above. An assessment where half the building was inaccessible produces a worse rating than the building deserves. ## The recommendation report An assessment produces a recommendation report alongside the certificate, listing improvements with indicative payback categories. It is a useful starting point and it is a generic one: it comes out of the methodology rather than out of someone thinking about your building commercially. Treat it as a prompt, not a plan. A contractor pricing the actual work, and an assessor modelling what each measure would do to your specific building, will tell you considerably more. ## Assess before you spend If you are about to commit meaningful capital, having the building modelled first tells you which measures move your rating rather than which measures move a typical rating. That is a modest fee against a large spend, and it occasionally changes the plan completely. ## Questions we get asked ### Can an EPC rating be improved without changing the building? ### What should I have ready for the assessor? ### Does the assessor test how the building performs? ### Should I get an assessment before doing the work? Sources - A non-domestic EPC is an asset rating: it is based on the fabric of the building and its services rather than on metered consumption. [A guide to energy performance certificates for the construction, sale and let of non-dwellings, DCLG, 2014](https://www.gov.uk/government/publications/energy-performance-certificates-for-the-construction-sale-and-let-of-non-dwellings) Last updated 8 October 2026 . - [Who can produce one Accreditation and the right level](https://commercialepcupgrades.co.uk/who-can-produce-a-commercial-epc) - [Improving the rating What to do with the result](https://commercialepcupgrades.co.uk/improve-commercial-epc-rating) - [How long it lasts When you need another](https://commercialepcupgrades.co.uk/how-long-does-a-commercial-epc-last) Next step ## Find out where your buildings actually sit Before you plan against a deadline it helps to know the gap. Tell us the building and one commercial contractor comes back with what it would take to close it. Or call [07367 293494](tel:+447367293494). Monday to Friday, 9am to 5.30pm.