HEM:EPC wrapper

The HEM:EPC wrapper refers to a software component being developed by the UK government to translate the technical output of the new Home Energy Model (HEM) into official Energy Performance Certificates (EPCs) for new and existing homes. It functions as a specialised layer that defines inputs, applies standardised assumptions, and converts raw data into EPC ratings and recommendations, replacing the current Reduced data SAP (RdSAP).

The wrapper sits around the core HEM engine, acting as a translator to produce EPCs. It specifically handles the calculation of new metrics for carbon, energy efficiency, and "smart readiness". Currently being developed this, it was still in consultation during early 2026, aiming at a full launch in 2025/2026. The principle of wrappers is to allow models to to carry detailed information but not require this for every application of the model but instead give the option for certain assumptions, balancing speed and accuracy. Another example of a wrapper is the FHS wrapper which the Future Homes Standard (FHS) wrapper, meaning it is to be used for building regulation compliance, once the FHS becomes standards.

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