Why Is My EPC Wrong? Common Causes Explained

An EPC that does not seem to match your property can be frustrating, particularly when you are selling, letting, remortgaging or planning improvement work. If you are asking, “why is my EPC wrong?”, the answer is often not that the assessor has ignored the property. It is usually that the certificate is based on limited evidence, standard assumptions, older records or details that need checking.

An Energy Performance Certificate is a regulated assessment, not a full building survey and not a prediction of your household’s actual energy bills. That distinction matters. A well-insulated home with high energy use can still receive a strong EPC rating, while a carefully managed household may spend less than the certificate suggests.

What an EPC rating is actually based on

For most existing homes, an assessor uses the Reduced Data Standard Assessment Procedure, known as RdSAP. They inspect the property, record key construction and heating details, take measurements and photographs, then enter the information into approved software. The software applies a standard method to produce the rating and recommendations.

The calculation considers matters such as wall, roof and floor construction, insulation, glazing, heating systems, controls, lighting and renewable technologies. It also uses standard assumptions about occupancy, heating patterns and energy prices. It does not account for whether you prefer the heating at 18°C, work from home, use a log burner every evening or have particularly low electricity use.

This can make an EPC feel inaccurate when compared with lived experience. However, a difference between your bills and the EPC is not, by itself, evidence of an error.

Why is my EPC wrong when I have made improvements?

A common issue is that the EPC is simply out of date. A domestic EPC can remain valid for ten years, even if substantial work has taken place after it was issued. If you have installed a new boiler, fitted solar panels, replaced single glazing, added loft insulation or improved heating controls, an older certificate will not update automatically.

The same applies where a previous owner carried out work but the assessor could not verify it at the time of inspection. EPC assessments must be evidence-led. Some measures can be identified during a visit, but others are hidden behind finishes or within roof spaces. An assessor cannot assume that cavity wall insulation, underfloor insulation or a particular type of construction is present without suitable evidence.

For example, a homeowner may know that insulation was installed several years ago, but if there is no paperwork, clear visual evidence or access to inspect it, the software may need to use a conservative default. That can result in a lower rating than expected. In this situation, invoices, guarantees, building-control documents, installer certificates and dated photographs can all be useful when arranging a new assessment.

Common EPC errors worth checking

Some EPCs do contain factual errors. Start by reading the certificate carefully rather than focusing only on the headline band. The property description and recommendation section often reveal where the issue lies.

Check the address, property type, number of bedrooms, total floor area and the date of assessment. Then review the construction details. Is the property recorded as a mid-terrace when it is actually an end-terrace? Are the walls described correctly? Has the loft insulation depth been recorded accurately? Is the main heating system, fuel type or hot-water arrangement correct?

Windows can also affect the outcome. An EPC may describe some glazing as single glazed where replacement units are in place, or record a mix of glazing where all windows have since been upgraded. Similarly, thermostatic radiator valves, smart controls, room thermostats and solar panels may be omitted if they were not present, visible or evidenced during the original visit.

Floor area is particularly significant. A measurement error, an unrecorded extension or a conversion that has changed the layout can alter the result. Small differences do not always change the band, but properties close to a threshold can be affected by even one or two input changes.

When the EPC may be correct, even if it feels unfair

Some results are surprising but still valid under the EPC methodology. Older homes with solid walls can score differently from newer cavity-wall properties, even where they are comfortable and well maintained. Electric heating, open fires and certain secondary heating arrangements may also produce results owners do not expect.

Listed buildings and traditional properties can be especially difficult. Their construction may not suit standard improvement recommendations, and some suggested measures may require specialist advice or consent before any work begins. A recommendation is generated by the calculation method. It is not always a practical instruction to carry out work exactly as written.

There is also a difference between a property’s energy efficiency rating and its environmental impact rating. One can improve without the other improving by the same amount. This is another reason to avoid judging the certificate from a single figure alone.

How to check an EPC before you challenge it

The best first step is to gather the facts. Find the EPC reference number, read the assessment date and compare the recorded information with the property as it stood on that date. If the property has changed since then, the certificate may have been accurate when issued but no longer represent the home today.

Next, collect supporting evidence for anything you believe is missing or incorrect. Useful documents include boiler installation certificates, service records, insulation invoices, solar PV commissioning paperwork, window guarantees, building-regulation approvals and photographs that clearly show the relevant measure.

Be realistic about what can be proved. A verbal confirmation that insulation is present may not be enough for an assessor to enter it. This approach protects the reliability of EPCs for buyers, tenants, lenders and landlords alike.

Asking for a correction or a new assessment

If you believe there is a clear factual mistake, contact the assessor or the company that issued the certificate first. Explain the point precisely and provide the evidence you have. A professional assessor should review whether the information used was correct and whether an amendment or further visit is needed.

The right remedy depends on the issue. A simple administrative error may be capable of correction. Where the property data needs to be checked again, or where improvements have been completed since the visit, a new EPC assessment is usually the more appropriate route. An assessor cannot alter a certificate merely because a higher rating is preferred.

If you cannot resolve a concern with the assessor, you can follow the complaints process through their accreditation scheme. Keep copies of the EPC, your correspondence and supporting documents. This is particularly useful where an incorrect rating is affecting a sale, tenancy or mortgage decision.

For landlords, timing is important. Do not wait until a new tenancy or marketing deadline to discover that an old certificate no longer reflects the property, or that its rating creates a Minimum Energy Efficiency Standards issue. A current, accurate EPC gives you time to consider the right improvements and retain the evidence for future assessments.

Choosing the right next step for your property

A reassessment is most worthwhile where there is clear evidence of missing upgrades, incorrect recorded details or a material change to the property. If the certificate is technically correct but the recommendations are unsuitable, energy-efficiency advice may be more valuable than repeatedly commissioning EPCs.

EPC Access can provide accredited domestic and commercial assessments, alongside practical support for landlords and homeowners considering their next steps. Bringing your evidence to the appointment and allowing access to relevant areas of the property helps the assessment run quickly and accurately.

An EPC should give a reliable snapshot of the building on the assessment date. If that snapshot no longer matches the property, checking the details early can prevent unnecessary delays when you need to sell, let or improve it.