Part L - SBEM

What SBEM does and what it does not do

SBEM means Simplified Building Energy Model. It is the simplified calculation engine used within the NCM for buildings other than dwellings. It applies standardised assumptions to building geometry, activity, construction, glazing, heating, cooling, ventilation, domestic hot water, lighting, controls and on-site generation. The NCM uses those assumptions to compare an actual building with a notional reference building consistently. (NCM Modelling Guide) (ADL2)

The calculation is an asset and compliance assessment, not a prediction of a particular occupier’s bills or carbon footprint. The operating hours, occupancy, internal gains and control patterns used in the NCM are standardised. Actual energy use also depends on tenant fit-out, management, weather, maintenance, setpoints, IT loads, operating hours and user behaviour. Approved Document L is explicit that Building Regulations compliance outputs should not be used directly as an actual-energy forecast. Where a project needs an operational prediction, that should be a separate, appropriately scoped exercise, such as a CIBSE TM54 assessment.

The distinction matters commercially. A low BPER or BER supports Part L compliance under the prescribed methodology. It does not guarantee a specific utility cost, operational rating or Energy Performance Certificate (EPC) grade. Equally, a detailed design model may be valuable for system design or operational analysis but is not automatically an approved Part L calculation.

The right question is therefore not simply, “Do I need SBEM?” It is: Does the building need a Part L calculation, which approved NCM implementation is suitable, and which formal outputs are required at each stage?

BER and BPER: the two key Part L comparisons

A successful non-domestic Part L calculation is not just a “carbon pass”. England’s 2021 regime requires two linked whole-building comparisons.

In Approved Document L, the full forms building emission rate and building primary energy rate should be used on first reference. BER, TER, BPER and TPER are common industry and BRUKL shorthand. These results are cumulative: passing BER does not excuse a BPER failure, and vice versa.(ADL2) (NCM Modelling Guide)

The performance approach gives design flexibility. The actual building does not need to replicate every feature of the notional building. A project may use a different coordinated combination of fabric, systems, controls and generation if it meets both targets and the other applicable requirements. It is not safe, however, to select a single feature—such as photovoltaic panels, a heat pump or a low U-value wall—and assume it will make the whole building compliant.

More than BER and BPER: limiting standards and services

The calculation tests sit alongside other Part L requirements. The 2021 guidance includes limiting standards for thermal elements and air permeability, services efficiency and control provisions, commissioning, information for owners and solar-gain checks for occupied or mechanically cooled non-residential spaces.

For example, the current Volume 2 recognised route gives a new-building air-permeability limiting value of 8.0 m³/(h·m²) at 50 Pa. This is a backstop, not a recommended universal design target. The measured result still has to be entered into the final calculation, and the as-built BPER and BER must still meet TPER and TER. A building can test below 8.0 and nevertheless fail one or both calculated rates. (ADL2)

This is why energy compliance should coordinate the architect, façade team, MEP engineer, contractor and air tester. The calculation must accurately reflect the final building; it cannot create performance after the air barrier, services route and control strategy have been fixed.

For a detailed explanation of test timing, pressure-test routes and common leakage points, see the planned Air Tightness Testing pillar page.

Part L 2026 and the Future Buildings Standard: what changes and when?

The Future Homes and Buildings Standards package was made and published in March 2026. For buildings other than dwellings, this is often referred to as the Future Buildings Standard. It is not a consultation draft. It is also not the general operative Part L standard for ordinary England work as at 5 September 2026.(ADL2 2026)

The distinction between publication, methodology and commencement is important:

For ordinary non-HRB work, the 2026 transition may preserve the prior requirements where the relevant building-control notice or full-plans application was submitted before 24 March 2027 and work on that particular building begins before 24 March 2028. HRB work has separate Gateway 2-based transition arrangements. The applicable route must be considered building by building rather than assumed across an entire development.

The Future Buildings Standard retains the non-domestic whole-building approach. The actual building is still assessed against a same-size-and-shape notional building, and the two central performance tests remain emissions and primary energy: BER against TER, and BPER against TPER. The as-built calculation still requires the constructed specification and measured air permeability where testing applies. (approved methodologies)

The published notional package is more demanding in several respects. The final policy position includes good fabric, low-carbon heating assumptions, enhanced lighting efficacy and heat recovery. For side-lit and top-lit non-domestic spaces, the notional building includes photovoltaic generation equivalent to 40% of the actual building’s foundation area, subject to defined exceptions. (FHS consultation)

That 40% figure needs the same careful explanation as a notional U-value or system type: it is a target-setting assumption, not a simple instruction that every actual commercial building must install precisely 40% PV. The actual design may vary if it satisfies both target rates and applicable limiting standards. The new L3 renewable-electricity functional requirement is directed to buildings that are, or contain, dwellings; it should not be presented as a blanket standalone commercial-building PV mandate.(FHS consultation)

The right preparation is to design for the future standard where the programme will fall under it, but to avoid premature claims. Before a 2026-regime calculation is issued, check the project’s transition position, the current NCM documents, the exact approved software implementation and the Building Control route.

New builds, extensions, conversions and change of use

Not every non-domestic project needs the same calculation. Correct classification at the outset avoids unnecessary modelling and, equally, prevents an extension or fit-out being missed because it is not described as a “new building”.

A material change of use can involve a building becoming a dwelling or gaining a flat. That is a warning not to default to Volume 2/SBEM. The dwelling portion needs the correct domestic Part L / SAP route, while genuinely non-domestic areas remain under Volume 2. Mixed-use schemes should define the boundary, services and evidence responsibilities early.

Air testing, EPCs, energy statements and Part O: connected but separate

Air-tightness testing and SBEM

Pressure testing is a practical example of why the final model matters. For relevant new non-domestic buildings, the current England guidance generally expects pressure testing, subject to defined exceptions. The measured air-permeability result must be used in the as-built BPER and BER calculation. If the building is below 500 m², an exception may allow testing to be avoided only by using an assumed 15 m³/(h·m²) at 50 Pa in the calculation. That is a conservative model input, not a permissible achieved result or evidence that the building performs at 15.

An air test and an SBEM report are therefore linked but not interchangeable. The test is fabric evidence. The as-built BRUKL is the calculation output that uses the measured result. A design assumption cannot replace a final test where testing is required. For test procedure, programme and remedial strategy, use the planned Air Tightness Testing page.

Non-domestic EPCs

An EPC is a related but separate legal output. Non-domestic EPCs use the NCM asset-rating framework and may share underlying data with the Part L calculation. On construction, the EPC Regulations set separate delivery, registration and notification duties. An EPC does not replace the Part L design/as-built calculations, pressure-test evidence, commissioning documentation or owner information.

This is especially important on shell-and-core projects and separately lettable units. Confirm the EPC boundary and expected fixed-services fit-out early with an accredited assessor. Refer readers to Non-domestic EPCs for the certificate route, rating and transaction triggers.

Planning energy statements

A planning energy statement is not a nationally standardised Part L certificate. It is usually required by an adopted local-plan policy, a planning condition or a local validation requirement. An SBEM result may be useful evidence, but it only helps if it addresses the requested boundary, baseline, target and stage of certainty. “Part L compliant” does not automatically mean “planning policy compliant”.

For planning-specific methodology, local-policy review and energy hierarchy work, link to Energy Statements.

Part O overheating

Part O is not a general non-domestic SBEM requirement. Current Approved Document O applies to new residential buildings and relevant residential parts of mixed-use schemes. A stand-alone office, retail unit, warehouse or industrial building does not become a Part O project simply because it has glazing, cooling or an SBEM model.

A mixed-use development can need several separate but coordinated workstreams: Volume 2 / SBEM for commercial areas; SAP for dwellings; and Part O evidence for the residential parts in scope. Facade changes, shading, opening areas, cooling and communal pipework can affect several workstreams. See the planned Part O Overheating page for a dedicated guide.

Start with the right Part L calculation route

A successful Part L SBEM project starts with classification and evidence control, not a late BRUKL upload. Before appointing an assessor, establish the building use and boundaries, jurisdiction, project type, total useful floor area, fixed-services scope, building-control application date, commencement position, HRB status and whether planning or EPC evidence is also required.

Energy Report can then help select an appropriate approved NCM route, develop realistic BER and BPER targets, review fabric and services options, prepare the design-stage submission, coordinate air testing and commissioning evidence, and update the model for the completed building. For domestic parts of a mixed-use scheme, begin the parallel Part L SAP Calculations workstream early rather than trying to apply one method to every area.

Contact Energy Report with the latest drawings, building use schedule, floor areas, MEP strategy, proposed fabric and glazing, renewable strategy, building-control dates and any existing energy models. The first task is to confirm the applicable route and software version, then build a calculation that can be delivered as designed and evidenced as built.