EPC Changes from 15 June 2025: What Landlords Need to Know About RdSAP 10

From 15 June 2025, a major change to how Energy Performance Certificates (EPCs) are calculated for properties in the UK. The new methodology, known as RdSAP 10, replaces the current RdSAP 2012 and brings with it the most extensive updates in over a decade.

So, what’s changing, and what should landlords do now?

Why the Update?

RdSAP is the standard method used to assess the energy efficiency of existing propertyies, feeding directly into the EPC rating (from A to G). EPCs are legally required when renting or selling a property and remain valid for 10 years.

RdSAP 10 aims to improve the accuracy and fairness of assessments by reflecting:

• More detailed property data

• The presence of low-carbon and smart technologies

• Real-world energy use patterns

It’s part of the UK’s broader strategy to reduce emissions and modernise the housing stock.

Key Changes in RdSAP 10

Here’s what landlords should know about the updated methodology:

1. Greater Data Accuracy

Assessors will collect more detailed measurements across a range of features:

• All windows must now be measured, including frame type and any permanent shutters

• Wall insulation is recorded by thickness and type, with support for thermal conductivity values (if evidence is provided)

• Roofs and floors now have additional options for construction type, insulation depth, and non-residential spaces above or below

2. Room-in-Roof Improvements

Loft conversions and attic rooms will be assessed under two new categories. Assessors will choose either a simplified or detailed method depending on the layout, with more precise measurements to reflect thermal performance.

3. Ventilation and Air Pressure Testing

RdSAP 10 introduces expanded ventilation options:

• Open chimneys, flues, and fireplaces can now be recorded

• Mechanical ventilation systems (e.g., MVHR) are better supported

• Air pressure test results can be included if verified, allowing airtightness to influence ratings more accurately

4. More Recognition of Modern Tech

A broader range of technologies is now supported in EPC modelling:

• Heat pumps, solar PV, battery storage, and PV diverters are all included

• Smart heating controls and hybrid systems (e.g. boiler + heat pump) can improve ratings

• Small-scale renewables like hydro generation are now factored in

5. Lighting, Hot Water & Basements

• Lighting is now counted by number of bulbs (not fittings), including how many are LED or CFL

• Hot water tanks are assessed by size and insulation where evidence exists

• Heated basements and converted spaces are modelled more accurately with updated U-values

How Will EPC Ratings Be Affected?

Not every property will see a major change in its EPC rating — but some will.

• Properties with low-carbon tech and proper documentation may see an improved score

• Properties using outdated or default assumptions could drop in rating

• Flats and converted buildings (like HMOs) may benefit from more accurate treatment of shared walls and internal layout

What Should Landlords Do Now?

1. Check Existing EPCs

If your EPC is due to expire soon, consider renewing before 15 June. Pre-update EPCs are still valid for 10 years — and may give a better result if your property lacks clear documentation.

2. Prepare Supporting Evidence

Having proof of insulation, heating system specs, or air pressure test results can make a real difference under RdSAP 10.

3. Plan Upgrades

Invest in improvements that are now better recognised, including:

• Wall, roof and floor insulation

• Low-carbon heating systems

• Smart controls and renewables

4. Stay Compliant

Rental properties must currently meet EPC rating of E (unless exempt). The government has proposed that all new tenancies must be for properties with a minimum EPC rating of C by 2028 (all privately rented properties by 2030), but there may be benefits in updating your EPC now before the next change in EPC methodology in 2026.

RdSAP 10 is a long-overdue update that makes EPCs more accurate, fair, and forward-looking. For landlords, it offers a better way to showcase energy improvements, but also increases scrutiny on properties with missing data.

Now’s the time to take stock, plan upgrades, and make sure your EPCs reflect your properties as they really are.

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