The National Insulation Association (NIA) has published the response it submitted to the government consultation on the Home Energy Model (HEM), the proposed replacement for the Standard Assessment Procedure (SAP) that will be used to demonstrate compliance with the Future Homes Standard. The consultation closed on 27 March 20241. The NIA represents the insulation industry in the UK, with members drawn from installers, system certificate holders and manufacturers1.
The consultation ran from 13 December 2023 to 27 March 2024 and set out two options for the low carbon technologies to be specified in newbuilds, both broadly retaining the standards in Building Regulations Part L and using a heat pump or low carbon heat network for space and water heating. One option also includes solar PV, wastewater heat recovery and decentralised mechanical ventilation2. The results of the consultation have not yet been published2. The Home Energy Model is intended to replace SAP, and the NIA said it expects the change to "shift the goalposts compared to SAP, most likely resulting in lower SAP scores and requiring higher standards of energy efficiency for compliance with building regulations"1.
The NIA welcomed several elements of the proposals, including the publication of open-source code, a centralised cloud-based model and the increased half-hourly time resolution, which it said would improve modelling of heat pump performance and the interaction with other building elements1. It raised concerns about the runtime of the model, saying a runtime of five minutes would most likely still be workable for industry, while 15 minutes or more would represent a substantial challenge for SAP users1. It also disagreed with the proposal to include the thermal mass of furniture in thermal mass calculations, and said the cost of listing products in the Product Characteristics Database is prohibitive for manufacturers, with the result that many products are not listed1.
"The NIA welcomes the move to publish the open-source code, as this will aid transparency and promote greater understanding of the methodology among relevant stakeholders."
The NIA also asked for clarity on accountability, saying it would welcome confirmation of whether the government, BRE or independent software providers would be responsible for the model1. On validation, it said the Marmalade Lane case study findings show the HEM was consistently more closely aligned with measured data than SAP 10.21. The consultation did not cover the EPC wrapper, which the NIA said would be consulted on later in 20241.
| Item | Detail |
|---|---|
| Consultation opened | 13 December 20232 |
| Consultation closed | 27 March 20241 |
| Response submitted by | National Insulation Association1 |
| Target carbon reduction | 75 to 80 per cent less than homes under current building regulations2 |
| Proposed heating | Heat pump or low carbon heat network2 |
Why it matters for households
The HEM will be the calculation engine behind compliance with the Future Homes Standard, which applies to new homes in England from 2025 and is intended to cut carbon emissions by 75 to 80 per cent compared with homes built under current regulations2. For a household, the practical effect is that the standard of a new home's fabric and its heating system will be judged by a different method, and the NIA expects that method to produce lower scores than SAP for the same building1. That bears on how much insulation, glazing and airtightness a new home carries, and therefore on how much energy it needs to stay warm. The consultation also proposes a Home User Guide explaining that heat pumps do not provide hot water in the way a combi boiler does, and giving guidance on thermal stores and off-peak tariffs2. Homes on a heat network, of which 446,517 in the UK are currently connected, would take their heat from a central source rather than an individual unit2. The NIA's point about the PCDB matters here too: if products are not listed because of cost, the technologies available to be credited in a calculation are narrower1.
What happens next
The government has not announced the final details of the standard or its implementation timeline2. The Future Homes Hub suggests new legislation will be published early in 2025 before full implementation later in the year, with a period of either 6 or 12 months between the regulations being set and coming into force, and a 12-month transition period for builds already in process2. The EPC wrapper is to be consulted on separately1.