Home Energy Model and Future Homes Standard SAP Calculations

Home Energy Model (HEM) and SAP 10.3 for the Future Homes Standard

We carry out Future Homes Standard SAP calculations in London and nationwide, and we'll run Home Energy Model (HEM) calculations as soon as HEM is approved. SAP calculations start from £100+VAT and take 3 working days once we have your drawings.

The Future Homes Standard (the new Part L) was published on 24 March 2026 and comes into force on 24 March 2027. If you are designing homes that will start on site after that, check them against the new rules now, not after planning.

What is the Home Energy Model?

The Home Energy Model is the government's replacement for SAP. SAP works out a home's energy use month by month. HEM works it out for every half-hour of the day.

That matters for the kit new homes now use. HEM models heat pumps, hot water cylinders, solar PV, batteries and smart controls in much more detail than SAP. The code is published openly by government.

Where things stand (checked 27 October 2026)

• SAP 10.3 is the only approved method for the Future Homes Standard in England.
• HEM is not approved yet. Government delayed it in June 2026 and says it will come in alongside SAP 10.3 "in the coming months". There is no fixed date.
• Once HEM is approved, SAP 10.3 and HEM run side by side for a period before HEM takes over. Industry expects that period to be about two years, with at least six months' notice before SAP is withdrawn.
• Work already started in SAP 10.3 is expected to finish in SAP 10.3, including the as-built reports and EPCs. No need to redo a scheme mid-way.
• EPCs for existing homes will also move to HEM. Government is aiming for the second half of 2027.

We'll update this page when the dates are confirmed. See Industry Updates for each change as it happens.

Which rules apply to your project?

The current rules (Part L 2021 and SAP 10.2) still apply to a building if both of these are true:

• the building notice, initial notice or full plans application for that building went in before 24 March 2027; and
• work on that building starts before 24 March 2028.

It is judged building by building, not site by site. "Started" means the foundations and ground floor structure are complete, not just the trenches dug. Higher-risk buildings (18 metres or 7 storeys and over, with at least two homes) have their own dates from 24 September 2027.

Older transitional arrangements, from the 2013 and 2021 changes, also end. Plots on old consents that haven't started by 24 March 2028 move to the new rules.

What the Future Homes Standard changes for your design

The new standard is set by a "notional" home: the same size and shape as yours, with a fixed specification. Your design has to match its results. You don't have to copy its specification; you choose how to get there.

Heating: a heat pump, not a gas boiler

Under Part L 2021 the notional home had a gas boiler. Under the Future Homes Standard it has an air source heat pump. Gas boilers aren't banned, but a gas, oil or LPG system is not expected to pass. Plan for a heat pump or a low carbon heat network from day one, including space for the cylinder and the outdoor unit.

What this looks like in practice: a typical developer house with a gas combi, some PV and good fabric that passes Part L 2021 misses the new carbon target by a very wide margin. Swap the boiler for a heat pump and it passes again, even without PV, but with far less headroom than it has today. Heat pump designs that pass easily now still need checking.

Solar PV on every new home

There is a new legal requirement, L3: new homes need on-site renewable electricity, in most cases solar PV. The amount is based on 40% of the ground floor area and is checked in the SAP. There are exemptions, including buildings of 18 metres and over and sites where PV can't give a reasonable output.

We size the PV in the SAP and show whether it meets the requirement. See solar PV for SAP and SBEM.

Fabric, air tightness and ventilation

The notional U-values are the same as Part L 2021, but the fabric energy efficiency target is tighter because of the other changes below. A design that only just meets the fabric target today can fall short under the Future Homes Standard. The changes:

• tighter air tightness in the notional home (4 against 5 under Part L 2021), so air tightness testing matters more;
• decentralised mechanical extract ventilation (dMEV) in the notional home, so check the ventilation testing at completion;
• waste water heat recovery on showers;
• calculated junctions still help. PSI value calculations and accurate U-value calculations are often the cheapest way to close a gap.

Flats and heat networks

Individual heat pumps don't always fit in flats, so many blocks will use a communal heat pump system or connect to a district heat network. The type of network changes the target the flats are measured against. A district network can only be treated as low carbon ("sleeved") if its operator declares that at least 90% of the heat comes from new or unused low carbon capacity. A communal system serving one building can't be sleeved, so its own plant has to do the work.

Tell us early which heat network you're connecting to. It can make the difference between a pass and a redesign.

London schemes: planning and building regulations

Most London schemes also need an energy statement for planning. The current GLA guidance is still based on Part L 2021 and SAP 10.2, while building control will check new schemes against the Future Homes Standard. We run both, so the two reports agree.

The draft new London Plan, consulted on in 2026, would move London energy statements from carbon targets to space heating and energy use targets. We'll update our energy statements when it is adopted.

More airtight homes with heat pumps can also run warmer in summer. Check Part O overheating at the same time, and move to a TM59 dynamic model if the simplified method won't work. If Part O can only be met with air conditioning, SAP 10.3 now gives the notional home cooling too, so the flat isn't penalised for it. Tell us early so the SAP and the overheating report match.

How we help

• Design stage: we run your current design in SAP 10.3 and tell you what needs to change to pass the Future Homes Standard. If the project can stay on Part L 2021, we tell you that too.
• Already have Part L 2021 SAPs? We copy the existing models into SAP 10.3 and show you the gap, without starting again.
• Blocks of flats: a block compliance report can't mix SAP 10.2 and SAP 10.3, so we keep each block on one version from the start.
• The affordable route: we test the options that cost least first (junctions, glazing, PV layout, heat pump choice) before thicker insulation.
• One team: SAP, Part G water, Part O, PSI values, U-values, energy statements, air, sound and ventilation testing. No passing results between consultants.
• Home Energy Model: once HEM is approved, we'll run HEM calculations alongside SAP 10.3, so you can pick the method that suits the scheme.
• As-built: we update the calculation to what was built and lodge the EPC.

What you get

• A design-stage SAP calculation and Part L compliance report (BREL) for each home type.
• A clear list of what needs to change to pass, with the cheapest options first.
• The PV size needed for requirement L3.
• As-built SAP calculations and the on-construction EPCs at completion.

What we need from you

• Plans, sections and elevations (PDF or DWG).
• Wall, floor and roof build-ups, and window specifications.
• Heating, hot water and ventilation details (or tell us and we'll suggest them).
• Which building regulations stage the project is at, and when it will start on site.

Price and turnaround

SAP calculations from £100+VAT. Turnaround: 3 working days once we have everything we need.

Multi-unit schemes and HEM calculations: send us the drawings for a free quote.

Our experience

We are accredited SAP assessors with Elmhurst Energy (membership EES/027276), with more than 17 years in energy assessment and more than 4,000 SAP calculations. We follow every change to the rules, so you don't have to.

Questions we get asked

Has the Home Energy Model replaced SAP?
Not yet. At 27 October 2026, SAP 10.3 is the only approved method for the Future Homes Standard. HEM will come in alongside it once government approves it, and the two will run side by side before HEM takes over.

When do I need to design to the Future Homes Standard?
If the building control application for a building goes in on or after 24 March 2027, or work on it starts on or after 24 March 2028, it must meet the new standard. If your scheme is close to those dates, design to the new rules now.

Can a new home still have a gas boiler?
Gas boilers aren't banned, but the target is now set by a home with a heat pump. In practice, a gas, oil or LPG system is not expected to pass. Plan for a heat pump or a low carbon heat network.

Do new homes need solar panels?
Yes, in most cases. Requirement L3 asks for on-site renewable electricity, based on 40% of the ground floor area. Buildings of 18 metres and over, and sites where PV can't give a reasonable output, are exempt.

Will HEM give a different result from SAP?
It may. HEM is more detailed, especially for heat pumps, hot water and PV. If a design only just passes in SAP 10.3, keep some margin. We'll run both once HEM is approved.

Can you check our Part L 2021 design against the Future Homes Standard?
Yes. If we already have the SAP, we copy it into SAP 10.3 and show you what fails and the cheapest fix. If not, send the drawings and spec.

How much does a Future Homes Standard SAP calculation cost?
SAP calculations start from £100+VAT, with a 3 working day turnaround. Send us the drawings by email or WhatsApp for a free quote.

Related: SAP calculations and EPCs, New Dwellings, solar PV for SAP and SBEM, PSI values and thermal bridging, U-value calculations, Part O overheating, energy statements, air tightness testing and Industry Updates.

Email your drawings or WhatsApp us for a free quote.