Home Energy Model: Future Homes Standard

Regulatory instruments

This guide covers the current official position in England. The live compliance position comes from the 2026 amendment regulations, the 24 March 2026 methodology notice, and the 2026 editions of Approved Documents L and F. The consultation responses explain policy, but users should treat those operative documents as the source of truth for what applies in practice.

Approved methodology

For now, SAP 10.3 is the only approved methodology for demonstrating compliance with the Future Homes Standard in England. Government says the Home Energy Model will follow as an approved calculation methodology after at least 3 months. There is no fixed HEM approval date yet.

Once HEM is approved, SAP 10.3 and HEM will run in parallel for at least 24 months before government moves to HEM as the sole methodology.

Key dates

The key implementation dates:

• 24 March 2026: the operative Future Homes Standard package was published, including the methodology notice and the 2026 editions of Approved Documents L and F.

• 24 March 2027: the new regulations come into force for most non-higher-risk building work.

• 24 September 2027: the same changes come into force for higher-risk building work.

Transitional arrangements

Transition is now applied building by building, not across an entire site. For most non-higher-risk work, the previous standard can still apply only where the relevant building notice, initial notice, or full plans application was submitted before 24 March 2027, and work on that specific building starts before 24 March 2028. For higher-risk building work, transition depends on a valid building control approval application being submitted before 24 September 2027 and not being rejected.

What the Future Homes Standard requires

The 2021 Part L uplift, which came into effect on 15 June 2022, delivered roughly 31% lower CO2 emissions for new homes than the previous standard.

The 2026 Part L packages has three material changes:

• The targets remain notional-building based, with a new reference services package.

  • There is no single universal emissions limit for all dwellings. Compliance is still assessed against dwelling-specific target primary energy, emissions and fabric rates generated from a notional dwelling with the same size, shape and orientation as the actual dwelling.

  • The main notional dwelling retains the 2021 uplift fabric values - roof 0.11 W/m²K, external wall 0.18, floor 0.13, windows 1.2, doors 1.0 - but moves from mains gas, natural ventilation with intermittent extract fans and air permeability 5 m³/h.m² @ 50 Pa to a notional air source heat pump equivalent to ErP A++, dMEV and air permeability 4 m³/h.m² @ 50 Pa. Wastewater heat recovery remains in the main notional specification.

• On-site renewables are a separate functional requirement.

  • Requirement L3 requires a system of on-site renewable electricity generation on the building or within its curtilage. For a dwellinghouse, one route is to show annual output equivalent to a PV array with 0.22 kWp/m² efficiency over an area equal to 40% of the ground floor area, facing south-east to south-west, at 45° pitch, and not overshaded. The alternative route is output equivalent to a PV array covering the reasonably practicable roof area at the same panel efficiency. For buildings containing dwellings, Approved Document L provides equivalent building-level, per-dwelling and reasonably-practicable-roof-area routes.

  • Lower solar provision is only allowed where justified and evidenced. Where the benchmark output cannot be met, the design should still maximise renewable generation output, including through higher-performance panels, alternative orientations and roof-layout changes where possible. Exceptional circumstances include cases where there is insufficient roof area to achieve 720 kWh/year for a dwellinghouse, or for buildings containing dwellings have insufficient roof area to achieve annual output equal to 720 kWh per dwelling divided by the number of storeys. Installations below the benchmark are highlighted in the BREL report, and supporting evidence for the reasonably practicable roof area or lower provision must be given to the building control body.

  • Appendix B gives example layouts for maximizing PV on different roof types and sets maintenance access route requirements to the roof edge: 2000 mm with no edge protection, 500 mm with a parapet, and 300 mm with either a man-safe system or railings.

• Stronger information, commissioning and handover requirements:

  • Approved Document L requires operating and maintenance instructions for fixed building services and any on-site electricity generation.

  • For newly erected dwellings, it also requires a Home User Guide covering heating and hot water, on-site electricity generation where applicable, ventilation and overheatin. The Home User Guide should be provided as both paper and digital, or as paper with a digital copy made available.

  • Owners of newly erected dwellings should also be given a signed as-built BREL report and photographic evidence of build quality, and the instructions should direct them to the as-built BREL report and the recommendations report generated with the on-construction EPC.

  • Approved Document F requires mechanical ventilation systems to be commissioned, the results of air flow rate testing for new dwellings to be provided to the local authority within five days of the final test, and the dwelling owner to receive the completed commissioning sheet plus operating and maintenance information, including design flow rates and maintenance requirements.

Expected Differences between SAP 10.3 and HEM

Based on current government documentation, several differences should be expected between SAP and HEM. These affect what can be modelled, what outputs are available, and how useful the model is outside a narrow compliance workflow. Vulcan’s objective is to make it easy to use HEM for use cases beyond compliance, and create more value for assessors and the wider ecosystem.

• HEM separates building physics from compliance assumptions. HEM has a core building physics engine, with separate “wrappers” used for compliance purposes. By contrast, SAP has compliance assumptions “baked in”. This means a HEM assessment can used with alternative assumptions, to understand performance under different conditions (e.g., following a TM59 methodology). HEM core calculations produce richer outputs that can be used to understand internal comfort, peak demand, and more.

  • For FHS compliance, the wrapper standardises the regulatory assumptions explicitly. The FHS wrapper standardises the calculation period and timestep, internal gains, heating and cooling schedules, cold-water temperatures, hot-water draw-off patterns, water-heating hours, window and vent behaviour, mechanical ventilation operation, intermittent curtain and blind shading, weather data, and post-processing fuel properties. Assumptions are required for comparable benchmarks - HEM makes these explicit and separable from the core engine.

• HEM is a dynamic simulation; SAP is a monthly approximation. Government describes SAP as a monthly-timestep method, whereas HEM simulates each half hour through the year. That gives HEM a stronger basis for modelling peak conditions, timing effects, and technologies whose performance depends on when demand and generation occur, including solar PV, batteries, heat pumps and time-of-use interactions. For space heating and cooling, SAP estimates demand from monthly heat loss, gains and setpoints; HEM solves heat-balance equations based on BS EN ISO 52016-1:2017.

• HEM models solar and shading more explicitly. Government says SAP calculates solar gains from monthly solar radiation adjusted for window size and orientation, and does not account for solar absorption through opaque elements. HEM instead calculates the position of the sun at hourly timesteps, resolves direct and diffuse radiation, applies this by element orientation and pitch, and includes solar absorption through opaque fabric. For shading, SAP uses broad overshading categories, while HEM distinguishes between shading from distant objects and window overshading. That makes HEM a stronger basis for testing design choices where solar exposure and shading actually matter.

• HEM treats ventilation and infiltration as a more explicit physical problem. SAP derives infiltration from measured airtightness using a simple rule of thumb, while HEM uses the same underlying airtightness measurement but applies a more detailed method that accounts for built form, shelter and hourly wind conditions (following BS EN 16798-7:2017). This means identical airtightness evidence may not produce the same infiltration losses under HEM as under SAP.

• HEM represents thermal mass more explicitly. SAP uses internal effective heat capacities, or “kappa values”, and includes only the part of the construction assumed to participate materially in short-term storage. HEM instead takes an areal heat capacity for the full build-up and adds a mass-distribution class to represent where that mass sits in the construction. This is a more physically explicit treatment of how constructions warm up and cool down over time, and will likely increase the modelled effect of thermal mass.

• HEM models hot-water distribution losses explicitly, rather than by default percentage. SAP assumes 15% of hot-water energy is lost through pipework. HEM models losses from properties such as pipe length, volume, insulation, temperature difference and tapping duration. For FHS compliance, some of these inputs are then estimated from building geometry, number of floors, building height, and number of wet rooms. This makes HEM more sensitive to actual design choices, while still simplifying entry of inputs for compliance purposes.

• HEM models heat pumps and emitters in situ rather than relying only on pre-calculated performance. SAP 10.2 represents heat pumps using pre-calculated methodology with generic assumptions about demand profiles. In HEM, heat-pump are explicitly modelled using system-specific test data, with the specific dwelling and timestep-level conditions, to calculate heat output, electricity draw and COP. HEM also does not assume emitters are simply “properly sized”, but can model their characteristics and warm-up behaviour more explicitly. That makes HEM a stronger basis for analysing system sizing, controls and peak performance.

• HEM produces richer outputs than the compliance metrics alone. The Future Homes Standard retains familiar Part L metrics such as TER, TPER and FEE. Delivered energy will be available as a voluntary reporting metric via the BREL report where HEM is used. HEM’s core structure also supports much richer simulation outputs than a simple pass/fail compliance result. This is important because it means the same model can support both regulatory reporting and wider building-performance analysis.

One important caveat: HEM:FHS is still standardised for compliance. The current FHS wrapper uses a single representative weather file for England, chosen partly to support consistency with SAP 10.3 during the transition. HEM’s full analytical potential is broader than the compliance wrapper currently allows. That is exactly why it is useful to distinguish between HEM for compliance and HEM for wider analysis.

Key Documents

The Future Homes and Buildings Standards: Building Circular 01/2026: https://www.gov.uk/government/publications/the-future-homes-and-buildings-standards-building-circular-012026

Methodologies for calculating the energy performance of new buildings in England: notice of approval (24 March 2026): https://www.gov.uk/government/publications/methodologies-for-calculating-the-energy-performance-of-new-buildings-in-england-notice-of-approval-24-march-2026

Approved Document L (2026), Volume 1: Dwellings https://www.gov.uk/government/publications/approved-document-l-2026

Approved Document F (2026), Volume 1: Dwellings https://www.gov.uk/government/publications/approved-document-f-2026

Home Energy Model: Future Homes Standard assessment https://www.gov.uk/government/consultations/home-energy-model-future-homes-standard-assessment

Home Energy Model: Future Homes Standard assessment: technical documentation https://www.gov.uk/government/publications/home-energy-model-future-homes-standard-assessment-technical-documentation

Standard Assessment Procedure https://www.gov.uk/guidance/standard-assessment-procedure