RdSAP 10: What Changed in October 2025 and What It Means for Your EPC

RdSAP 10 is the updated Reduced data Standard Assessment Procedure methodology that replaced RdSAP 9.94 in October 2025. All new EPC assessments in England and Wales must use it. The key changes: updated carbon and primary energy factors, revised default U-values for older constructions, better treatment of heat pumps, and LED assumed as the single low-energy lighting type.

What is RdSAP and why does it matter?

SAP (Standard Assessment Procedure) is the UK government-approved method for calculating the energy performance of dwellings. The full SAP is used for new buildings; the Reduced data SAP (RdSAP) is used for existing homes, "reduced" because some inputs are estimated from construction type and age rather than directly measured.

RdSAP determines your EPC rating. The methodology sets the rules for what data the assessor collects, what defaults apply when data is unavailable, and how inputs are weighted in the final score. Changes to RdSAP can change ratings even if nothing about the property has changed.

RdSAP 9.94 had been in use since 2012, over 13 years without a major update. RdSAP 10 is a significant revision.

The main changes in RdSAP 10

1. Updated carbon emission factors

The most far-reaching change is the update to carbon emission factors for different fuel types. The grid electricity carbon factor has fallen significantly since 2012, reflecting the growth of wind, solar, and nuclear in the UK electricity mix.

Under RdSAP 9.94, electricity had a relatively high carbon factor because it reflected the 2012 grid (heavily fossil-fuel dependent). Under RdSAP 10, the electricity carbon factor is substantially lower, reflecting the current grid.

Effect: Properties heated by electricity, particularly heat pumps, but also electric storage heaters, have lower modelled carbon emissions under RdSAP 10 than under 9.94. Properties heated by natural gas see their relative position worsen slightly because gas carbon intensity hasn't changed while electricity's has improved.

2. Revised treatment of heat pumps

RdSAP 9.94 had a simplified treatment of heat pumps that didn't fully account for their coefficient of performance (COP) across different operating temperatures. RdSAP 10 includes more accurate modelling:

• The COP of the heat pump varies with outdoor temperature and flow temperature
• Underfloor heating (low flow temperature) is credited more than radiator systems (higher flow temperature) when paired with heat pumps
• The building fabric performance is more closely linked to heat pump efficiency modelling

Effect: Heat pumps in well-insulated homes score significantly better under RdSAP 10. A heat pump in a poorly insulated home gains less benefit from the methodology change.

3. Revised default U-values for older constructions

RdSAP 10 updates the default U-values (heat loss rates) for wall, floor, and roof constructions in each age band. Some of these have been revised upward (worse) based on thermal imaging and in-situ measurement research showing that real-world heat loss is higher than previously modelled.

Affected constructions:

• Solid brick walls from pre-1930 period: default U-value revised upward
• Some cavity-wall constructions from 1960s–1970s: revised based on measured data
• Suspended timber floors in pre-1930 properties: revised upward

Effect: Properties with these construction types may see a marginal SAP score decrease compared to what the same property would have scored under RdSAP 9.94. This is more accurate, not a penalty.

4. LED assumed as the single low-energy lamp type

RdSAP 9.94 distinguished between compact fluorescent lamps (CFLs) and LEDs. RdSAP 10 treats all low-energy fittings as LED, because CFLs are no longer manufactured for new installation and existing ones are being replaced.

Effect: Properties with a mix of CFL and LED fittings are no longer penalised for having CFLs (which were less efficient than LEDs in 9.94's model). The lighting credit for a "fully low-energy" property is the same regardless of CFL vs LED. This is a neutral-to-slightly-positive change for most properties.

5. Changes to conservatory treatment

RdSAP 10 updates how conservatories and extensions are treated. Unheated conservatories attached to the main building now have revised thermal buffering values. Heated conservatories are included in the heated floor area calculation with updated default U-values for their glazed construction.

Effect: Properties with conservatories may see minor changes in SAP score. The direction depends on construction quality and whether the conservatory is heated.

6. Updated primary energy factors

Primary energy factors (which convert delivered energy to the energy consumed in extraction, processing, and distribution) have been revised for all fuel types. These affect the EPC's primary energy indicator rather than the SAP score directly.

What hasn't changed

Reassurance matters here, because methodology changes cause anxiety among landlords with recently issued EPCs. The following remain identical under RdSAP 10:

• The A–G band structure, SAP 69+ is still C, SAP 55–68 is still D, SAP 39–54 is still E. The thresholds have not moved.
• The core data collection process, assessors still visit and record the same categories: wall type, roof, glazing, heating, hot water, lighting. The form of the assessment is unchanged.
• The 10-year validity period, EPCs issued under RdSAP 9.94 remain valid for their full 10-year term. The methodology change is not a reason to renew.
• The MEES framework, the minimum E standard still applies; the proposed C standard by 2028–2030 is unchanged.
• The government EPC register, certificates are still lodged at the same register; the interface and search function are unchanged.
• The accreditation schemes, Elmhurst, ECMK, Quidos, and other approved schemes continue to operate as before.

Do you need to re-assess your property?

No, if: Your existing EPC was issued under RdSAP 9.94 and is within its 10-year validity. The old certificate remains legally valid for selling or letting.

Yes, if:

• Your certificate has expired (over 10 years old)
• You've made improvements since the last assessment and want the updated rating
• You want to ensure your rating reflects the latest methodology (relevant if your SAP score is close to a band boundary)

If your property is close to the C band boundary under an old 9.94 certificate, a new RdSAP 10 assessment may move you into C, particularly if you have a heat pump or use electricity as the primary heating fuel. It's worth getting reassessed if you're within 3–4 SAP points of the target band.

Practical implications for London landlords and sellers

For landlords managing MEES compliance, RdSAP 10 changes are mostly minor. The minimum E standard (SAP 39+) and proposed C standard (SAP 69+) use the same SAP thresholds, the methodology update doesn't change what score you need.

However, if you're in a portfolio where some properties are borderline (SAP 67–68 under 9.94), it's worth getting a fresh assessment. Some will have moved to C under 10.0; others may have shifted down slightly.

For sellers, the practical impact is similar. If your agent or solicitor is querying a borderline rating, a fresh assessment under RdSAP 10 may resolve the question with better data.

We carry out all assessments under RdSAP 10 as required across all London boroughs, including Tower Hamlets, Hackney, Ealing, Bromley, and 30 others. Book an assessment or see our pricing page. For more on what the assessment process involves, see our what happens during an EPC assessment guide.