Home Energy Model delayed as SAP 10.3 remains approved route
UK – The launch of the Home Energy Model has been delayed, with SAP 10.3 remaining the only approved methodology for assessing the energy performance of new homes.
The update, published by the Department for Energy Security and Net Zero, confirms that the Home Energy Model has not launched alongside the Future Homes Standard. The government said the decision was taken during the final stages of internal assurance, to ensure the model is robust before it goes live.
The Home Energy Model, or HEM, is intended to replace the Standard Assessment Procedure, better known as SAP, as the calculation method used to assess the energy performance of homes. It has been developed as part of a wider move towards a system better suited to net zero housing.
For housebuilders, energy assessors, consultants and low-carbon heating specialists, the delay provides short-term certainty but also extends the transition period before the new approach is introduced.
SAP remains central to new-home compliance because it is used to demonstrate compliance with Part L of the Building Regulations. It is also used to produce Energy Performance Certificates, which are relied on by homeowners, landlords, buyers and renters.
Why SAP is being replaced
SAP has played a central role in housing energy assessment for many years, but the way homes are designed and heated is changing.
New homes are becoming more reliant on electricity, with heat pumps, solar PV, battery storage, smart controls and more advanced hot water strategies becoming increasingly common. These technologies do not always fit neatly into simplified monthly assumptions, because their performance can vary depending on outdoor temperature, occupancy, solar generation, hot water use, control settings and time of day.
One of the main differences with HEM is the move to half-hourly calculation periods, rather than the monthly calculation approach used in SAP. This is intended to give a more detailed view of domestic energy performance by assessing how a home performs across shorter time intervals.
That distinction matters because modern low-carbon homes are increasingly designed as connected energy systems. Heating, hot water, ventilation, fabric performance, on-site generation and controls all interact. A model based on shorter time periods should be better able to reflect those interactions than a simplified monthly calculation.
For the heat pump sector, this is particularly relevant. The route used for compliance can influence design decisions, technology selection and how different systems are valued within new-home specifications. A methodology that better reflects electricity use, system temperatures, hot water demand and weather conditions could help give a clearer assessment of low-carbon home design.
What the delay means
The current position means SAP 10.3 remains the practical compliance route while HEM undergoes further assurance work. The government has said HEM will be introduced alongside SAP 10.3 in the coming months, with final preparations focused on guidance, assurance and sector readiness.
The government’s SAP guidance now lists SAP 10.3 as the current version of SAP and RdSAP 10.0.1 as the current version of Reduced Data SAP.
Although the delay may be seen as another pause in the transition to a new assessment regime, it also reflects the importance of getting the model right. As homes move further towards low-carbon heating, on-site generation and smarter energy use, the calculation behind compliance becomes increasingly important.
For now, the message to industry is clear: continue working with SAP 10.3, but remain ready for the Home Energy Model to follow.
