On June 15th, 2025, a new calculation engine called RdSAP 10 was introduced for domestic Energy Performance Certificates (EPCs). As a result, there are significant changes to how Domestic Energy Assessors (DEAs) are required to collect and enter information for EPCs.
Why has RdSAP 10 been introduced?
The new RdSAP10 methodology will enable more accurate EPCs to be created which better reflect the energy performance of individual buildings. In the last decade there have been significant technological improvements which can now be taken account of within the EPC. RdSAP 10 will also make many fewer assumptions about aspects such as glazing, lighting and ventilation which will improve the accuracy of the report.
What extra information do assessors need to collect?
There is a total of 32 changes to the EPC system! Assessors will need to collect additional information on aspects such as roof rooms, ventilation, lighting and insulation types and thicknesses. However, by far the biggest change going forward is that assessors will need to take individual measures for all windows present within the property. For larger properties which have a lot of glazing presents this will add a significant amount of time to how long an assessor will need to spend both on the property as well as creating the EPC.
What does this mean for my EPC?
Your EPC will have less assumptions, it will be a more accurate representation of the property and provide you with more information and data about how your property is performing. To account for the additional time required to collect and enter all the extra data, Assessors will need to account for the extra work and time involved with each report and a price increase should be expected for obtaining an EPC.
What happens next?
Well from 15th June only RdSAP10 will be able to be used to produce EPCs for existing buildings. However, there are likely to be further changes to the EPC in the next 2 years.
The Government have recently consulted on EPC reform where they are proposing wholescale changes so that the EPC can be more useful document and accurate to the Government’s environmental policy aims. They are also consulting on the minimum energy efficiency standards for private rented properties.
More information on these consultations can be found: