Have you recently found yourself staring at an EPC label and wondering what the coloured A–G scale really means?

You are not alone. Searches for “energy efficiency labels and symbols” have risen by 125,000% this week, with millions of people learning how to interpret the rating attached to a property. The country is suddenly decoding the energy label, and that is a positive step.

However, the honest translation is more nuanced than “A is good and G is bad”.

An Energy Performance Certificate is a useful, standardised benchmark. It helps you compare properties and understand modelled energy costs. But it is not a complete description of your home, and it is not a retrofit design.

Here is what your EPC genuinely measures, what it does not tell you, and why a PAS 2035 Retrofit Assessment goes much further.

First, what the A–G scale actually is

The headline EPC rating is the Energy Efficiency Rating, shown as a score from 1 to 100 and grouped into bands from A to G.

• A represents the most energy-efficient homes within the scale.
• G represents the least energy-efficient homes.
• The arrow shows the property’s current rating.
• A second marker shows its potential rating if the recommended improvements are carried out.

The certificate will also include a list of suggested improvements. These may include loft insulation, wall insulation, heating upgrades, glazing improvements, solar photovoltaic panels or heating controls.

For existing homes, the assessment is normally produced using Reduced Data SAP, or RdSAP. This is a standardised methodology designed to assess existing dwellings using information that can be observed, measured or reasonably assumed during an EPC survey.

The headline rating is primarily based on the estimated running costs associated with:

• Space heating
• Hot water
• Lighting

The calculation uses standardised assumptions about factors such as occupancy, heating patterns and thermostat settings. This makes EPCs broadly comparable between properties, but it also means the result is not a record of one household’s actual energy bills.

The EPC may also show an Environmental Impact Rating, which presents the property’s modelled carbon emissions on a separate A–G scale.

That distinction matters. Today’s headline EPC rating is largely a cost-based model, while the environmental rating is expressed in carbon terms. Neither should be mistaken for a detailed investigation of the building fabric, its condition or the way occupants use it.

The three things your EPC rating does not tell you

1. It does not measure how much energy your home actually uses

An RdSAP assessment is a model. It is not a meter reading.

The methodology deliberately uses standard assumptions so that properties can be assessed consistently. Where construction details cannot be established without opening up walls, floors or ceilings, the calculation may rely on defaults based on factors such as the building’s age, type and visible characteristics.

That is useful for comparison, but it cannot account fully for:

• How many people live in the property
• Which rooms are heated
• How long the heating operates each day
• Individual thermostat settings
• Whether occupants work from home
• How residents use hot water and lighting
• Personal comfort preferences

Two homes with similar layouts and identical EPC ratings can therefore have very different energy bills and comfort levels.

This difference between modelled performance and real-world performance is often described as the performance gap. It does not mean the EPC is “wrong”. It means the certificate is answering a narrower question:

How does this property perform under a standardised calculation?

It is not answering:

How much energy will your household actually use?

2. It does not measure the condition or build quality of what is already there

An EPC records what can be established during a relatively limited assessment. It does not provide the same level of investigation as a whole-house retrofit survey.

A label will not normally tell you whether:

• Insulation is continuous behind a wall
• There are gaps or compression in loft insulation
• Thermal bridging exists around junctions, corners or openings
• A cavity wall contains insulation that has failed or become uneven
• Windows and doors are fitted and sealed correctly
• The building is sufficiently airtight
• Moisture is present within the construction
• Existing ventilation is adequate
• Previous measures have been installed to an appropriate standard

These details can have a significant effect on comfort, energy use and building safety.

For example, a wall may be recorded as insulated, but the EPC cannot necessarily confirm whether that insulation is continuous around window reveals, floor junctions and service penetrations. Those weak points can become thermal bridges, creating colder internal surfaces and increasing the risk of condensation.

Likewise, improving airtightness without considering ventilation can create unintended problems. A more efficient building still needs a safe and effective way to remove moisture and maintain indoor air quality.

We know this from more than 15 years of hands-on experience. We started on the tools as retrofit installers, so we have seen the difference between what a certificate suggests and what a building actually does on site.

3. It does not tell you what to do, in what order or at what cost

The recommendations on an EPC are useful starting points, but they are not a detailed retrofit plan.

They do not normally set out:

• The correct sequence for installing measures
• How one measure will interact with another
• Whether the property is suitable for a particular insulation system
• What ventilation strategy is required
• Whether the construction is solid wall, cavity, traditional or heritage
• The likely disruption to occupants
• The full project cost
• Whether the proposed measures represent good value for money
• Whether the property may qualify for a genuine cost-cap exemption

Retrofitting a solid-wall or traditional property is not the same as upgrading a modern cavity-wall home. The building’s construction, exposure, moisture behaviour and existing alterations all need to be considered.

An EPC recommendation might say “install internal wall insulation”. A proper retrofit process must ask more questions:

1. Is internal insulation technically suitable?
2. How will junctions and reveals be treated?
3. What happens to existing moisture movement?
4. Will the measure reduce floor area?
5. How will ventilation be maintained?
6. What is the cost per unit of improvement?
7. Is there a better whole-house solution?

That is the difference between an improvement suggestion and a professional design approach.

Why the energy label is changing anyway

The government has acknowledged that the current single-metric EPC system is insufficient for the future of energy efficiency policy.

The proposed reformed approach will present four headline metrics:

1. Fabric performance: how effectively the walls, roof, floor, windows and doors retain heat.
2. Heating system: the efficiency and carbon intensity of the heating system.
3. Smart readiness: the property’s ability to use smart controls, flexibility and related technologies.
4. Energy cost: an estimate of typical energy running costs.

Energy use and carbon emissions are expected to remain available as secondary information.

In practical compliance terms, the proposed approach is based on fabric performance plus a choice of either the heating system metric or smart readiness metric.

The new Home Energy Model (HEM) methodology is expected to be available for calculation from late 2027 and is expected to run alongside RdSAP during the transition period until October 2029.

This means an EPC C on today’s certificate may not be equivalent to an EPC C under the new metrics.

If you are a landlord planning for EPC C by 2030, check the certificate date carefully. Under the proposed transition arrangements, a property rated EPC C or above under the existing system before 1 October 2029 may be grandparented until the certificate expires or is replaced.

Do not rely on the rating alone. Review the certificate’s issue date, expiry date and the evidence behind the assessment.

What a Retrofit Assessment adds

A PAS 2035 Retrofit Assessment looks at the dwelling as a whole rather than treating the EPC rating as the complete picture.

A qualified Retrofit Assessor considers matters including:

• Property condition
• Construction type and age
• Existing and previous energy efficiency measures
• Occupancy and household needs
• Ventilation
• Moisture and condensation risk
• Building fabric and thermal performance
• Interactions between proposed measures
• The evidence required to support the retrofit plan

This whole-house approach is central to safe and effective Energy Efficiency Retrofit. It helps ensure that measures are suitable for the property and installed in an order that reduces risk.

At CPH Retrofit, our services can also support the wider process:

• Retrofit Assessment to establish a reliable technical baseline.
• Retrofit Coordination to keep assessment, design, sequencing, installation and evidence aligned with PAS 2035.
• Retrofit Measure Modelling to compare measures and value for money before you commit expenditure.
• Air Pressure Testing to establish an airtightness baseline and help verify building performance.
• C3 Technical Monitoring to provide independent quality assurance and compliance monitoring.

Skipping the assessment stage can be expensive. Poor sequencing, unsuitable insulation, inadequate ventilation or incomplete installation can lead to defects that require Retrofit Remediation Services later.

What landlords and property owners should do now

1. Find your current EPC and check the expiry date.
   Do not assume that an old certificate will remain suitable for future compliance decisions.

2. Treat the EPC as a benchmark, not a design document.
   It is valuable baseline information, but it does not replace a technical survey.

3. Commission a PAS 2035 Retrofit Assessment.
   A qualified Retrofit Assessor can investigate the property’s condition, construction, occupancy and risks.

4. Model the measures before committing spend.
   Compare the likely performance improvement, cost, sequencing and suitability of each option.

5. Plan for the whole house.
   Consider fabric, heating, ventilation, airtightness and occupant needs together rather than installing isolated measures.

6. Keep the evidence.
   Retain EPCs, assessment reports, design information, installation records, testing results and monitoring evidence. This is essential for compliance and future decision-making.

Your EPC is the starting point, not the finish line

The A–G energy label is useful because it gives you a consistent way to compare properties. It can highlight potential improvement opportunities and provide an important starting point for landlords, homeowners, housing providers and retrofit professionals.

But it does not measure your actual energy use, confirm the condition of your building or design the right retrofit pathway for your property.

That is why we look beyond the label.

With more than 15 years of practical installer experience, our team understands how thermal bridging, insulation continuity, airtightness and ventilation affect real buildings. We combine that practical knowledge with PAS 2035 expertise to provide reliable, evidence-led Retrofit Coordination Services.

If you need clarity on your property’s current performance, future requirements or the best route towards a safe and cost-effective retrofit, contact CPH Retrofit today.

We will help you move from simply reading the label to understanding what your building actually needs.

This article reflects published policy and guidance available in September 2026. EPC metrics, implementation arrangements and regulatory requirements remain subject to further government updates. For current compliance obligations, always check the latest official guidance and obtain project-specific professional advice.