The Future Homes Standard (FHS) is set to be introduced in England, the date of which is to be confirmed. Its primary aim is to significantly enhance the energy efficiency of new homes and reduce carbon emissions, supporting the UK’s broader strategy to achieve net zero by 2050.
Under the FHS, new homes must produce 75–80% fewer carbon emissions compared to those constructed under 2013 regulations.
Homes built to the FHS must also be ‘zero-carbon ready’ and designed so they won’t require retrofitting to benefit from the decarbonisation of the electricity grid and the transition to electrified heating. The use of gas and oil boilers will not be allowed in new homes, with heating provided instead by low-carbon technologies such as heat pumps and heat networks.
The Home Energy Model (HEM) is a government calculation methodology designed to assess the energy performance of homes across the UK to the FHS. The model is designed to eventually replace SAP.
Latest Information February 2026
The Government has confirmed that an updated version of SAP (SAP10.3) will be used as an interim methodology, and will be used to calculate compliance with the FHS as part of a phased transition for new build homes.
The date for the change to SAP 10.3 is to be confirmed.
The HEM will be launched three months after the release of the FHS.
Both SAP 10.3 and HEM will then be used as dual compliance for the FHS for a period of 24 months before SAP is taken away and the only method of compliance for the FHS will be the HEM.
We will of course offer the new HEM assessments alongside our SAP assessments once HEM goes live.
The Future Homes Standard and Home Energy Model
Many are just getting used to the latest version of SAP, despite it being around now for 3 years or so. But coming soon as some big changes in how we will be assessing new build residential, and what they assessed for.
The Future Homes Standard (FHS)
The Government is introducing a new FHS which all new homes must meet. The FHS will contain several detailed elements but focuses on improving heating and hot water systems and reducing heat waste.
Measures proposed include enhanced building materials and glazing standards and low-carbon heating technologies such as Air Source Heat Pumps (ASHPs).
Homes built to the FHS must also be ‘zero-carbon ready’ and designed so they won’t require retrofitting to benefit from the decarbonisation of the electricity grid and the transition to electrified heating. The use of gas and oil boilers will not be allowed in new homes.
Under the FHS, new homes must produce 75–80% fewer carbon emissions compared to those constructed under 2013 regulations.
There will also be new standards for a material change of use, like an office to residential for example.
To show compliance with the FHS a new methodology is being developed, called the Home Energy Model (HEM)
Home Energy Model (HEM)
This methodology is completely different to the current SAP as we know it and will go into a lot more detail regarding the information that will be required for a calculation.
In short term, The Government has confirmed that both SAP (SAP 10.3) and the Home Energy Model (HEM) will be used to calculate compliance with the Future Homes Standard (FHS) as part of a phased transition for new build homes.
SAP 10.3
SAP 10.3 will have the following changes:
• A new notional dwelling used to set the primary energy, carbon emission and fabric energy efficiency targets of the upcoming Future Homes Standard.
• The Primary Energy Factor for electricity is increasing from 1.5 to 1.96, which means the Primary Energy figure in SAP 10.3 will be higher than it is in 10.2 without any other changes although this shouldn’t make compliance any more difficult as the notional dwelling will be changed from a gas boiler to a heat pump.
• The Carbon Factor for electricity is decreasing from 0.136 to 0.086, which means the Carbon Emissions in SAP 10.3 will be lower than it is in 10.2 without any other changes.
• However, if the proposed new dwelling is to have a gas boiler as its main heating source, even with a significant amount of solar PV, it’s very unlikely to pass Building Regulations 2021. The way forward, if you didn’t know it already, is for heat pumps.
• The Full Revised carbon emission and primary energy factors for fuels used are in SAP Table 12.
• There are changes to way District Heating and Communal Heating will be input.
• A new version of the BREL report to clearly show SAP 10.3 has been used to calculate compliance with the Future Homes Standard.
• SAP 10.2 will be used to calculate compliance with the Building Regulations 2021
• SAP 10.3 will be used to calculate compliance with the Future Homes Standard.
What’s the difference between HEM and SAP?
There are many ways HEM will calculate the dwelling compared to SAP, which should make the calculation much more accurate to the actual building and should reduce the performance gap.
• Increasing the time resolution – SAP undertakes calculations at a monthly time step. In contrast, the HEM will simulate homes at a 30-minute time resolution, meaning that every half-hour of the simulated year is evaluated.
• Modelling energy flexibility and smart technologies – As a result of the HEM running as a half-hourly simulation, it can accept varying profiles. This creates the potential to take unique values for every half-hour of the year, allowing for realistic modelling of the interactions between variable supply and demand and enabling accurate measurement of the benefits from storage and load shifting technologies and behaviours.
• A revised database of product characteristics – The government plans to rebuild the Product Characteristics Database (PCDB) from the underlying test data and to add new classes of products to fully integrate all existing technologies into the model and PCDB.
• Using ‘wrappers’ to distinguish different use cases.
The HEM will only be used initially to demonstrate compliance with the FHS, so that would be one of the wrappers. But going forward there will be another wrapper for EPCs, and further wrappers for other uses like PAS 2035 Retrofit, or Existing dwelling EPCs. The HEM will be the central mechanism for these.
Having seen what is involved in the input for the model the main thing that springs to mind is how detailed and complicated it will be. It’s significantly more complex that SAP. Much as there are many similarities between SAP and HEM the amount of detailed data that will be required is significant. And I wonder, how geared up the industry is to provide this?
HEM – Here are few highlights:
- FHS will use regional weather data rather than UK average for compliance metrics
- Occupancy based on recent data from the English Housing Survey and uses floor area and number of bedrooms to calculate occupancy.
- Lighting details entered per zone with energy use based on performance data and solar gains into the dwelling, and Internal heat gains from lighting also included in calculation.
- HEM makes a much more detailed analysis of distant shading, ie from other buildings etc
- HEM will enable the dwelling to be split into two zones, and for each the fabric loss heat is assessed individually at half hour intervals.
- The orientation of the Building can be input accurately to anywhere within 360 degrees and not just the 8 standard directions.
- For Walls, Roofs and Floor types there are many more data input fields, and the thermal mass of each element will now be taken through the whole element and not just the first 100mm or so from the internal surface. In fact, the calculation for thermal mass also includes many more data input fields too.
- Perhaps the most difficult for industry will be the increased data requirements for windows and doors. Every opening must be input individually with its own characteristic, like U values, solar g value, area of glass and opening area, amongst others.
- For Ventilation and Infiltration, we will need to know a lot more information, for example, area of air bricks and trickle vents, much more performance data on ventilation systems, and their ductwork.
- In space heating, which accounts for one of highest impact inputs on the final results, the calculation methodology has been improved with much more detail. As such the input required is very high in terms of information. It’s likely the FHS notional dwelling will be based on a heat pump. There are inputs available for other forms of electric heating including Heat Batteries.
- Its not just the heat source, their emitters, radiators and underfloor heating require much more input. In HEM heat output is determined by the emitter characteristics and the temperature difference between the emitters and the surrounding air, and their responsiveness dependent on the thermal mass of the emitter system.
- Hot water demand is measured in half hourly timesteps HEM can calculate demand based on actual length and frequency of hot water events. There is improved modelling of water storage systems based on number of hot water events. The seasonal variation in mains cold water is accounted for and pipework losses fully modelled.
- Finally, as you may have noticed by now, like all the other inputs the information required for renewables, Solar PV, Batteries and Diverters is also improved with much more detail required. Half hourly timestep allows a more comprehensive calculation of PV output.
Distant shading will directly influence PV output. And more details of the PV panels and supporting infrastructure needed.
Final Thoughts
There you have it, a (not so) brief intro to FHS and HEM. Big changes to come, I think for us assessors its building on what we already do and getting used to the two new ways of reporting compliance, SAP 10.3 and HEM.
For our clients and architects etc my initial thoughts are that there is an awful lot more, detailed information, that is going to be required to complete a full HEM assessment, and are they going to be able to provide that? For the building fabric information an architect should be able to, but the work involved will take longer.
For the M&E side there is a lot of information required that looks like it could only come from an M&E specialist.
So, the time it takes to undertake an assessment, even after all the information is provided, will be considerably longer than it is for SAP, and therefore more expensive. Likewise, the time spent by the architect will be longer and more expensive, it may be necessary to employ a M&E specialist, and finally the builder will have to spend longer ensuring not only is the build to the spec standard, but also in recording the required information to allow completion.
Watch this space.