Guide
Improving a commercial EPC rating: what actually moves it
Updated
The rating comes out of a model, so the measures that move it are the ones the model is sensitive to. That is not always the same as the ones that feel most obvious.
How the rating is produced
A non-domestic EPC rating is not a measurement of your energy bills. It is the output of a calculation, run under the government's approved methodology, using standardised assumptions about how the building is used. That has two consequences worth internalising. First, changing occupant behaviour does not change the rating. Second, an improvement that produces a large real-world saving may move the rating less than a smaller measure that the model treats as significant, and vice versa.
Measures that typically move a non-domestic rating
- Lighting. Efficient luminaires and, importantly, controls such as occupancy and daylight sensing. In lighting-dominated buildings like offices and retail this is usually the highest-yield area.
- Heating and cooling plant efficiency. Replacing old, inefficient plant is a large intervention with a correspondingly large modelled effect.
- Controls and zoning. Time and temperature control, weather compensation and zoning are modelled and are often cheaper than plant replacement.
- Ventilation and heat recovery, particularly where mechanical ventilation serves a large proportion of the floor area.
- Fabric: insulation and glazing. High capital cost and disruptive in an occupied building, but permanent.
- On-site renewable generation, where the roof and the structure allow it.
- Metering and, where applicable, building management system capability, which the methodology takes account of.
How to plan the work properly
- Start from the recommendation report attached to the existing certificate. It is the model's own view of what would help.
- Ask the assessor to model specific measures before you spend. This is consultancy rather than part of the certificate fee, and it is far cheaper than doing works that do not move the rating.
- Sequence around tenancies. Works are easier and cheaper between lettings, and a rating problem discovered during a deal is the most expensive time to discover it.
- Check the interaction with the minimum standard and with any exemption you might otherwise register: see the MEES guide.
- Reassess after the works, and make sure the new certificate is lodged on the register.
- Keep the evidence: specifications, commissioning records and the assessment inputs. If a rating is ever challenged, that file is your answer.
Two traps
- Improving the building without remodelling it
- The certificate does not update itself. Works only change the rating once a new assessment has been carried out and lodged.
- Assuming a payback exemption is easy
- Exemptions have conditions, evidence requirements and expiry dates, and they are registered on a self-certification basis, which means the risk of getting it wrong stays with the landlord. Treat an exemption as a considered position, not a shortcut.
Which measures will move your rating depends on your building's model, and cannot be determined from a web page. Ask an accredited non-domestic assessor to model the options for your specific property before committing to capital works.