What is a commercial EPC?

A commercial EPC — formally a non-domestic Energy Performance Certificate — rates the theoretical energy efficiency of a commercial building from A+ to G. It is a legal requirement at the point of construction, sale or letting, and it is the document MEES enforcement is built on.

What the certificate contains

Every commercial EPC shows an asset rating: a number and band calculated by comparing the building's modelled CO₂ emissions against a notional benchmark building of the same size and use. A score of 0 would be a zero-emissions building; the bands run A+ (negative net emissions) through to G. The certificate also records the floor area, the main heating fuel, the assessment level used, and the assessor's accreditation details.

Alongside the certificate sits a recommendation report — a ranked list of improvements with indicative paybacks, from lighting controls through to plant replacement. Landlords planning MEES work usually start from this report, although the costed options in it are generic and worth validating before committing capital.

What it measures — and what it deliberately ignores

The assessment is an asset rating, not an operational one. The assessor models the building fabric (walls, roof, floor, glazing), the fixed building services (heating, cooling, mechanical ventilation, hot water, lighting) and the building geometry. Plug loads, occupant behaviour, opening hours and process energy are all excluded by design.

This is the single most misunderstood point about commercial EPCs. A warehouse running 24/7 with electric space heaters can out-rate an efficient nine-to-five office, because the certificate models the installed systems rather than the meter readings. If the question you actually want answered is "where is our energy spend going", that is audit territory rather than EPC territory — see the difference explained by specialists in commercial energy auditing.

Levels 3, 4 and 5 — how assessor qualifications map to buildings

Non-domestic energy assessors qualify at one of three levels, and the building's complexity dictates the minimum level allowed to certify it:

• Level 3 (NDEA L3). Simple buildings: natural ventilation, basic heating systems, no significant cooling. Covers a large share of small shops, offices and industrial units. Modelled in SBEM using standard templates.
• Level 4 (NDEA L4). Buildings with air conditioning, complex HVAC, atria up to a defined scale, or unusual construction. Most modern office and retail stock falls here. Still SBEM, but with full system-by-system input.
• Level 5 (NDEA L5). Buildings whose performance cannot be represented adequately in SBEM — large atria, automatic blind or daylight control, night cooling, complex ventilation strategies. These require Dynamic Simulation Modelling (DSM), which simulates the building hour by hour across a full weather year.

A certificate produced by an assessor below the required level is invalid. When you request a quote we confirm the level from the building description before pricing, because getting this wrong wastes both the fee and the lead time — and lead time is usually the scarce commodity when a transaction is waiting.

SBEM and DSM in one paragraph each

SBEM (Simplified Building Energy Model) is the government's calculation engine for most non-domestic assessments. The assessor zones the building by activity, enters fabric and services data, and SBEM computes annual energy use against the notional building. It is fast and consistent, but conservative: where evidence is missing, it assumes defaults that usually worsen the rating.

DSM (Dynamic Simulation Modelling) runs a full thermal simulation — typically in software such as IES VE or TAS — capturing solar gain, thermal mass and control interactions hour by hour. It is the only permitted route for Level 5 buildings and is considerably more expensive, but for sophisticated buildings it often produces a fairer rating than SBEM's simplifications would.

When the law requires a commercial EPC

• On construction of a new commercial building, before handover.
• Before marketing a building for sale or for let — the EPC must be available to prospective parties free of charge.
• On certain major refurbishments that change the number of designated units or the fixed services.
• Continuously, in effect, for let property: MEES makes it unlawful to continue letting sub-E stock without a registered exemption. The MEES guide covers this in full.

Exemptions exist for some building categories — places of worship used for worship, temporary buildings with a planned life under two years, stand-alone buildings under 50 m², and industrial sites with low energy demand. The exemption tests are narrower than most owners assume, so it is worth checking before relying on one. The government's official guidance on commercial property EPCs at gov.uk sets out the legal position.

Validity and renewal

A commercial EPC lasts ten years from lodgement. There is no legal duty to renew early if nothing triggers a new certificate — but a 2017-vintage rating built on old conventions can materially misstate where the building stands today, in either direction. Many landlords renew ahead of refinancing or lease events precisely to avoid negotiating against stale numbers. Typical fees by building type are on the cost page, and the assessment process page explains what happens on the day.