The consultation for the Future Homes Standard proposes that the Standard Assessment Procedure (SAP) be replaced by the Home Energy Model (HEM), according to an assessment published by Stroma Built Environment on 15 July 20241. SAP has been the recognised method of calculating data for an Energy Performance Certificate since 2002, and is used to demonstrate compliance with Part L in England and Wales, Section 6 in Scotland and Part F1 in Northern Ireland1.
Under the current system, SAP calculations must be carried out using approved software built on an engine approved by the BRE, and must be conducted by a certified SAP assessor, with results subject to quality assurance through the government-approved certification process1. The calculation compares the dwelling being designed against a notional building, checking energy consumption, emissions and fabric efficiency against the required levels of Part L1. The EPC is an output from the SAP calculation, produced at the as-built stage, and shows the notional running cost of the dwelling as a band from A to G, where A is the lowest cost and G the highest1.
The Home Energy Model will work similarly to SAP, but with more detail around occupancy, weather data and heat loss from sources such as pipe runs1. Stroma states that the HEM tool available within the consultation suggests the required calculations will be more involved, take more time and therefore cost more to complete, and that specifics on the efficiencies and other advantages of individual HEM solutions are yet to be seen1.
"Within HEM is an ASHP, making gas boilers increasingly difficult to comply with, alongside a fabric specification, reduced airtightness targets, and potential provision for PV"
The notional dwelling within HEM includes an air source heat pump, alongside a fabric specification, reduced airtightness targets and potential provision for photovoltaic panels1. Stroma describes Approved Document L, Conservation of Fuel and Power, as part of the government's carbon reduction strategy, contributing to the target that all emissions reach net zero by 20501.
| Item | Current position under SAP | Proposed position under HEM |
|---|---|---|
| Calculation method | SAP, since 2002 | Home Energy Model |
| Detail covered | Standard inputs | More detail on occupancy, weather data and heat loss, including pipe runs |
| Notional dwelling heating | Not stated in the source | Air source heat pump |
| Cost and time | Not stated in the source | More involved, more time, higher cost |
Why it matters for households
The method behind a home's energy rating determines what the certificate on a new build actually measures. A model that accounts for occupancy patterns, local weather data and heat loss from pipe runs is intended to reflect how a dwelling performs in use rather than only how it is designed1. For a household, the practical effect is that the rating attached to a new home may rest on a more detailed set of assumptions than the SAP-based ratings attached to older properties, which affects how EPC ratings for new build homes compare with older homes. The assumptions behind those ratings are set out in the SAP, RdSAP and the assumptions behind home energy ratings guide.
The inclusion of an air source heat pump in the notional dwelling points to a shift in how new homes are expected to be heated, which bears on a household's exposure to fuel prices and on home heating and energy independence. The Future Homes Standard and new build heating guide covers the heating provisions in more detail. The consultation also sets out two approaches to carbon reduction, compared in Future Homes Standard Option 1 vs Option 2, and the expected scale of emissions reduction is set out in how much lower carbon emissions will be in new homes under the Future Homes Standard.
What happens next
The Home Energy Model sits within the Future Homes Standard consultation, and the tool used to run scenarios is available within that consultation1. Stroma states that specifics on the efficiencies and other advantages of individual HEM solutions are yet to be seen1. No commencement date for the replacement of SAP by HEM is given in the source, and no confirmation that the proposal will be adopted as consulted on has been reported.