RdSAP – Reduced Data SAP.

The UK energy calculation methodology that’s used for existing properties

For existing buildings, a simplified version of SAP called Reduced Data SAP (RdSAP) is used to assess the energy performance.

An RdSAP assessment will use a set of assumptions about the property based on conventions and requirements at the time the building was constructed.

RdSAP was developed in the early 2000s as part of the work to develop the framework for the introduction of Energy Performance Certificates (EPCs) in 2007. It was developed by the BRE, Elmhurst Energy and Sava (who at the time were called National Energy Services). RdSAP was based on the combined proprietary methodologies of Elmhurst and Sava.

RdSAP is used in existing dwellings based on a site survey of the property, when the complete data set for a SAP calculation is not available. It consists of a system of data collection together with defaults and inference procedures that generate a complete set of input data for the SAP calculation.

The calculation starting from reduced data is done in two stages. First the reduced data set is expanded into a full data set, and then the SAP calculation is undertaken using the expanded data set. The actual SAP calculation is therefore identical, whether starting from a reduced data set or a full data set.

RdSAP is periodically updated. The current version of RdSAP is v9.94 and is still based on the version of SAP called SAP 2012. SAP itself has since been updated to SAP 10. RdSAP is currently being updated to be compatible with SAP 10, and it’s anticipated that a new version of RdSAP will be launched in Spring 2024.