What domestic landlords and homeowners need to know
Starting 15 June 2025, the UK’s method for calculating Energy Performance Certificates (EPCs) is being overhauled marking a significant shift toward accuracy and transparency. The new methodology, RdSAP 10, replaces RdSAP 9.94 and introduces a more detailed, evidence-based assessment of home energy efficiency. If you’re a landlord aiming to stay compliant with MEES regulations or a homeowner planning energy-saving upgrades, it’s crucial to understand what this means for you.
🏡 Why is RdSAP changing?
The UK has one of the oldest and least energy-efficient housing stocks in Europe. To meet its goal of reaching Net Zero by 2050, the government is enhancing EPCs to better reflect current technologies and support smarter retrofit decisions.
With that in mind, RdSAP 10 has been introduced to:
Deliver more accurate EPC ratings
Incorporate modern upgrades like solar panels and heat pumps
Provide better retrofit advice
Support efforts to cut carbon emissions and tackle fuel poverty
🔍 What’s changing in RdSAP 10?
Here’s a breakdown of the key updates that will reshape how properties are assessed:
1. Window Measurements
Previously, window data was estimated based on property age.
Now, every window is measured individually—width, height, glazing, frame, draught-proofing, and orientation are all recorded.
This results in more precise heat-loss calculations, especially in homes with upgraded windows.
2. Walls and Age Bands
A new Age Band M has been added for properties built in 2023 or later.
Mixed wall types can be recorded separately, improving accuracy.
Shared walls, such as those in flats or terraced houses, are also treated more precisely.
3. Rooms in Roofs
Loft conversions and attic rooms now receive more detailed assessments.
Assessors can select simplified or detailed entries, including slope, insulation and wall types.
4. Floors
Ground, intermediate, and upper floors are now assessed separately.
Each floor’s construction type (e.g. timber, concrete) and insulation levels are recorded.
5. Hot Water Systems
Details now include cylinder size (litres), heat loss and number of bathrooms.
Systems like solar water heating and heat pump cylinders are now recognised.
6. Heating Systems
Assessors now record:
Boiler make, model, and fuel type
Number of heating zones
Heating type (radiators or underfloor)
Control features like thermostats or timers
Multiple heating systems can be recorded
7. Ventilation and Airtightness
Systems such as MVHR, extractor fans, passive vents, and chimney blocks are now included.
If available, air pressure test results can be added to the assessment.
8. Lighting
- Instead of noting only fittings, assessors now log each bulb type (LED, halogen, CFL, incandescent), allowing for a more granular evaluation.
9. Smart Tech and Renewables
Recognised technologies now include:
Solar PV systems with battery storage
Solar diverters
Micro-CHP
Smart meters and advanced heating controls
10. U-Values and Heat Loss
- Updated U-values for walls, roofs, and floors align with current insulation standards.
11. Evidence-Based Data
Assessments rely more heavily on verified data like photos, documents, and product labels.
When no evidence is available, default values are used—which can lower your EPC rating.
12. New Calculation Engine
The new engine is powered by SAP 10.2, incorporating real fuel prices and updated carbon factors.
This ensures ratings better reflect true energy cost and environmental impact.
📉 Will my EPC rating change?
It’s likely. Properties without 
documented upgrades may see a drop in rating, whereas homes with renewables or improved insulation could see an increase.
Key influences on your EPC score include:
Property age and construction
Efficiency of heating systems
Quality of insulation
Availability of evidence
🧾 How to prepare as a landlord or homeowner?
✅ Organise your paperwork
Collect installation certificates, product manuals and air pressure test results.
Keep everything in one place for easy access during assessment.
✅ Upgrade where you can
Replace older bulbs with LEDs
Enhance loft and wall insulation
Install smart heating controls
💼 What this means for landlords
Minimum Energy Efficiency Standards (MEES) remain in place—meaning landlords must ensure properties meet an EPC rating of E or above to legally rent in England and Wales.
To stay ahead:
Create a digital folder for all energy upgrade records
Choose an accredited assessor who understands RdSAP 10
Consider a pre-assessment to spot potential rating issues early
🏁 Final thoughts
RdSAP 10 marks a significant step forward in the way homes are evaluated for energy efficiency. While the new process demands more upfront documentation, it ultimately produces fairer and more accurate EPC ratings.
For landlords, this update offers a pathway to future-proofing rental portfolios. For homeowners, it presents a compelling reason to embrace smarter, greener solutions. Either way, now is the ideal time to get informed,and take action.
