What is RdSAP 10? .
RdSAP 10 is the latest version of RdSAP used for producing Energy Performance Certificates for existing dwellings from 15th June 2025.
The RdSAP 10 update, using the latest SAP 10.2 methodology, aims to deliver more accurate energy efficiency calculations and help homeowners identify effective improvements.
The update from 9.94 includes:
Window Measurements
All windows must now be measured individually, replacing previous assumptions based on property age and type. This change ensures the heat loss wall area is correct, and hence the improvement in the SAP rating or reduction in carbon emissions from insulation measures can be more accurately calculated.
Sheltered Walls
DEAs must select if a sheltered wall in a flat or maisonette is adjacent to a stairwell or an unheated corridor, as these now have different U-values to reflect the differing thermal characteristics.
Roof Room Assessments
In order to better calculate the impact of roof rooms, additional measurements of gable and/or common walls are required. This ensures more accurate heat loss calculations and benefits from roof room insulation.
Additional Age Band
A new age band has been introduced for properties built from 2023 onwards, reflecting changes in Building Regulations. The new age band will be used to infer some data, such as thermal bridging assumptions.
Additional Insulation Thicknesses
RdSAP 10 includes new thicknesses for wall, roof, and floor insulation types, allowing for a more accurate assessment of insulation effectiveness.
PV batteries and diverters
RdSAP 10 includes PV batteries and PV diverters, which allows the calculation to more accurately assess how much of the generated electricity is used in the dwelling.
Mechanical Ventilation and Air Tightness
RdSAP 10 allows the inclusion of specific whole-house mechanical ventilation systems from the product database. In previous versions of RdSAP, only default systems could be included, which did not reflect the high efficiency and low electricity use of the system. An air-tightness test result can also be included to better reflect the air-tightness of newer dwellings and those that have had a deep retrofit.
New Carbon Emissions Factors
The carbon emissions factors have been updated in SAP 10.2, in particular for electricity. The carbon emissions for electricity have gone from 0.5kg per kWh down to 0.13kg per kWh. This reflects the decarbonisation of the grid and will impact electrically heated properties as well as those with micro-generation.
New EPC Recommendations
The EPC recommendations have been revised to include new RdSAP data items such as PV batteries and PV diverters. Heat pumps are now included in the EPC recommendations.
Change to distribution loss factor for community heating
The distribution loss factor is a factor applied to the space heating requirement of the property to account for losses between the heat generator and the dwelling. This is now dependent on the age band of the property, rather than being a fixed factor. With newer properties having a higher distribution loss factor.