RdSAP 10: What does it all mean?

The Building Research Establishment (BRE) has recently released information on the updated Reduced Data Standard Assessment Procedure, known as RdSAP. The updated version, RdSAP 10 is expected by spring 2024. VOR’s Technical Expert, Pete Marsh offers his insights into what these changes will mean in practice.

What is RdSAP?

RdSAP, short for the Reduced Data Standard Assessment Procedure, is the UK’s officially approved methodology for evaluating the energy performance of existing residential properties and generating Energy Performance Certificates (EPCs).

Originating in the early 2000s, RdSAP laid the groundwork for the introduction of Energy Performance Certificates (EPCs) in 2007. RdSAP primarily serves the purpose of assessing existing dwellings in situations where the complete dataset required for a standard SAP (Standard Assessment Procedure) calculation is not readily available. Instead, it relies on default values and data collected during on-site visits by assessors to calculate energy performance.

Although RdSAP has undergone several updates, it currently stands at RdSAP 2012 version 9.94, aligned with SAP 2012. In contrast, SAP has progressed to version 10 and is used for newly constructed dwellings in England, Wales, and Scotland. RdSAP is poised to catch up, with an anticipated refreshed version expected by the spring of 2024.

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What has changed?

This major update, set to launch in early 2024, aims to enhance the accuracy and comprehensiveness of energy assessments for residential properties and align with evolving energy efficiency practices and technologies, but it will bring about significant alterations that may impact the work of energy and retrofit assessors and preparation is key:

  • Comprehensive Window Measurement: Assessors will now be required to measure all windows, departing from the previous practice of assuming typical glazing areas based on a property’s age. This change aims to provide a more accurate reflection of the property being assessed.
  • Additional Options for Roof Rooms: Assessors will need to take additional measurements to account for the various construction types of common wall and gable walls in roof rooms.
  • New Age Band:  RdSAP 10 introduces a new age band specifically for properties constructed from 2023 onward. This addition allows for the display of improvements in U-values.
  • Inclusion of the Isle of Man: RdSAP assessments can now be conducted in the Isle of Man, alongside England, Wales, Scotland, and Northern Ireland. This inclusion expands the geographical scope of assessments.
  • Accounting for PV Diverters and Battery Storage: Assessors will be able to consider photovoltaic (PV) diverters and battery storage when present in a property, reflecting the growing use of these technologies.
  • Increased Emphasis on Heat Pumps: Heat Pumps, recognized as the government’s preferred low-carbon solution, will be recommended more frequently as an improvement measure under specific conditions, such as when the property is adequately insulated.


Pete’s view:

Overall the update has many positives:  more accurate assessments and more precise data, plus a move towards heat pumps, but there are some areas that still need clarification or may cause debate within the industry:

  • The requirement to measure all windows in RdSAP is a long-awaited improvement, as the current method based on property age and assumptions is inaccurate. This change should lead to more precise heat loss predictions, particularly since windows are a significant source of heat loss.
  • While recommending heat pumps in RdSAP is a positive step, there are some caveats. In some cases, the new recommendations might only apply to well-insulated homes. This could lead to missed opportunities for heat pump adoption, especially in properties needing fairly minor insulation upgrades.
  • RdSAP’s increased options for assessors during property surveys, including insulation, PV, lighting, and ventilation choices, are seen as a positive development, promising more accurate assessments.
  • It appears that RdSAP still doesn’t consider airtightness, which can significantly impact heat loss and has other risks. This omission may cause some debate.
  • RdSAP’s use of different fuel prices compared to SAP prevents direct software comparisons, which is not ideal.
  • The requirement for more on-site time may enhance data collection but could lead to higher EPC survey costs, potentially discouraging some individuals and companies.

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