The process of carrying out energy assessments on homes in the UK underwent its most significant change in over a decade in June 2025. A major software update, RdSAP 10, was launched by the Department for Energy Security and Net Zero (DESNZ) to provide more accurate energy performance ratings. This supports the Government’s carbon reduction goals and helps improve the UK’s housing stock by making homes warmer and more comfortable.
What Is RdSAP?
RdSAP 10 is the latest iteration of the Reduced Data Standard Assessment Procedure, which is the methodology used by energy assessors in the UK when estimating the energy performance of domestic properties.
RdSAP is a simplified version of the Standard Assessment Procedure (SAP). Both RdSAP and SAP serve the same purpose: producing EPC (Energy Performance Certificate) ratings for residential properties in the UK. While SAP is used for new-build properties with detailed design specifications, RdSAP has been specifically developed to assess existing dwellings where complete technical information may not be readily available.
The methodology standardises the Energy Performance Certificate (EPC) process, which rates homes on a scale from A (most efficient) to G (least efficient). These certificates are not merely regulatory requirements; they serve as crucial tools for homeowners, buyers and policymakers to understand energy consumption patterns, identify improvement opportunities, and track progress towards national carbon reduction targets.
What Does RdSAP Offer?
The RdSAP software provides a systematic approach to assessing a property’s energy rating. Domestic Energy Assessors (DEAs) collect data about the building's construction, heating systems, insulation levels, and other factors that influence energy performance. This data is entered into the RdSAP software to calculate an energy rating (A-G).
During a typical assessment, the assessor records details about the property's dimensions, construction materials, and installed systems. This information is then processed through sophisticated software that models the building's energy consumption and carbon emissions under standardised conditions. The resulting EPC provides both a current energy rating and potential ratings achievable through recommended improvements.
What Key Changes Did RdSAP 10 Introduce?
The transition to RdSAP 10 introduced fundamental changes designed to enhance accuracy and provide more meaningful assessments. The changes are part of the Government's aim of eliminating fuel poverty, lowering carbon emissions, and creating healthier and more comfortable dwellings.
Date Built
To help better categorise newly built homes, RdSAP 10 has introduced a new property age band (M). Band “M” applies to properties built in 2023 and onwards in England, Wales, and Northern Ireland. For Scotland, it applies to properties built in 2024 and onwards.
Comprehensive Window Assessment
Perhaps the most significant change involves window measurement requirements. Assessors are now required to measure all windows, moving away from previous practices that relied on assumed glazing areas based on property age. The total area, glazing and gap type, and frame type of every window must be assessed.
This represents a fundamental shift from the previous approach, where assessors could classify glazing as "typical," "more than typical," or "less than typical" without exact measurements. The updated requirement ensures that the actual thermal performance characteristics of each window are properly captured, leading to more accurate heat loss calculations and more targeted improvement recommendations.
Enhanced Insulation Data Collection
Insulation data is now collected in a greater range of increments for walls, roofs, and floors, allowing for a more detailed assessment of thermal performance. This improved approach enables assessors to better reflect the varying insulation standards found in existing properties, particularly important given the diverse age and construction types across the UK housing stock.
Detailed Roof Room Assessment
For properties with roof rooms (such as a loft conversion), RdSAP 10 now offers assessors the choice between two different room-in-roof types. This allows for a more precise assessment of these spaces. The difference between the two room-in-roof types is dependent on the existence of a common wall shared with the floor below. Both roof room types can follow either a simplified or detailed assessment. The detailed assessment is required where there are differing levels of insulation.
This improvement addresses a common source of inaccuracy in previous assessments, where converted loft spaces and roof rooms often have unique thermal characteristics that standard assumptions fail to capture.
Advanced Ventilation Options
RdSAP 10 features more options for ventilation assessment. Previously, assessors only needed to measure ventilation from open fireplaces, but the categories now include extractor fans, blocked chimneys, flues, and stack vents. This offers clearer insights into a home's ventilation. This upgraded ventilation assessment is crucial for understanding indoor air quality implications and the interaction between energy efficiency measures and adequate ventilation provision.
Improved Wall Assessment Options
RdSAP 10 allows assessors to select two alternative walls per building part, particularly helpful for assessing flats which may have different wall exposures (e.g., one sheltered, one exposed). This flexibility eliminates the previous requirement to split properties into extensions when dealing with varying wall constructions, streamlining the assessment process while maintaining accuracy.
The Benefits of RdSAP 10
The move to RdSAP 10 brought with it several significant benefits for homeowners, the property market, and national energy policy. The introduction of RdSAP 10 has been generally well-received for its more accurate assessments and precise data, addressing some previous concerns about the reliability of energy performance ratings.
More accurate assessments provide homeowners with better information about their properties' actual energy performance, leading to more informed decisions about improvement investments. The enhanced detail in window and insulation assessment will enable more targeted retrofit recommendations, potentially improving the cost-effectiveness of energy efficiency improvements.
From a policy perspective, the improved data quality will support a better understanding of the national housing stock's energy performance, informing future regulations and support schemes. This enhanced evidence base is crucial for tracking progress toward net-zero carbon targets and identifying where interventions are most needed.
Summary
The long-awaited RdSAP 10, which was initially due to be released in spring 2024, represents a pivotal progression in the evolution of domestic energy assessment in the UK. By moving toward more detailed, measurement-based evaluation methods, the RdSAP 10 methodology offers more accurate, reliable energy performance data needed to support both individual property decisions and national energy policy objectives.
More precise energy assessments will ultimately influence more comfortable, efficient homes across the UK. Stakeholders across the property and energy sectors are now faced with a new era of energy performance assessment that will better serve homeowners and the broader goal of decarbonising the UK's housing stock.
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