What an SBEM calculation is
SBEM — the Simplified Building Energy Model — is the calculation tool inside the National Calculation Methodology (NCM) for buildings that are not dwellings. It was developed by BRE and does for a commercial building what SAP does for a house: it takes the building’s areas and volumes, U-values, heating, cooling, lighting, ventilation and any renewables, and compares the result against a notional building of the same size, shape and use built to a reference specification. Beat the notional building and you comply.
The NCM also allows an approved Dynamic Simulation Model (DSM) instead of SBEM. Most buildings do not need one; some cannot be done properly without one. More on that below.
What Building Control actually checks
Under the 2021 edition of Approved Document L Volume 2, four things have to be right, and they are checked independently:
- CO₂: the Building Emission Rate (BER) must not exceed the Target Emission Rate (TER).
- Primary energy: the Building Primary Energy Rate (BPER) must not exceed the Target Primary Energy Rate (TPER).
- Limiting fabric standards: every element has a worst-acceptable U-value — 0.26 W/m²K for walls, 0.18 for floors and flat roofs, 0.16 for pitched roofs, 1.6 for windows and curtain walling, 2.2 for rooflights — and the building’s air permeability must not be worse than 8.0 m³/(h·m²) at 50 Pa.
- Limiting services standards: minimum efficiencies for the heating, cooling, lighting and ventilation plant.
A building can pass on carbon and fail on primary energy, or pass on both and fail on a single U-value. The output that records all of this — the document Building Control receives — is the BRUKL report, and it shows the target and actual figures side by side.
When you need one
Any new building that is not a dwelling and uses energy to condition its indoor climate — offices, retail, industrial units with heating, schools, leisure, hotels, the commercial floors of a mixed-use block. A material change of use can trigger the requirement too. Extensions are handled under the rules for new thermal elements rather than by an automatic full calculation, and there is a separate consequential improvements duty when you extend or add services to an existing building over 1,000 m².
The regulations exempt a short list: buildings used primarily as places of worship; temporary buildings with a planned time of use of two years or less; industrial sites, workshops and non-residential agricultural buildings with low energy demand; and stand-alone buildings with a floor area under 50 m². Listed buildings and buildings in conservation areas are exempt only where compliance would unacceptably alter their character. An unheated shell is outside Part L until somebody heats it — at which point it comes straight back in.
Two calculations, not one
This is the part that catches projects out. Regulation 27 requires:
- A design-stage notice, before work starts — the target rate, the as-designed rate, and a list of the specifications the calculation depends on.
- An as-built notice within five days of completion — the target rate, the as-constructed rate, and either confirmation that the building was built to the listed specification or a list of everything that changed.
Design stage is where a fail is cheap: a lighting spec, a glazing ratio, a heat pump instead of a gas boiler. As-built is where substitutions on site — the cheaper glazing, the different rooflight — turn a pass into a fail with the building already standing. We run the design-stage model, tell you what it is sensitive to, and keep the model so the as-built update is a revision rather than a restart.
The EPC is a separate duty
The non-domestic EPC comes from the same SBEM model but it is a distinct legal requirement under the Energy Performance of Buildings Regulations: the person carrying out the work must give an EPC to the building owner within five days of completion and notify the local authority of its reference number. It has to be produced by an accredited non-domestic energy assessor. Because we produce the BRUKL and the EPC from one model, the two documents agree with each other — which is not a given when they come from different people.
Levels 3, 4 and 5 — and when SBEM is not enough
Non-domestic assessors are accredited at three levels, and the level your building needs decides both the fee and the programme:
- Level 3 — simple, naturally ventilated buildings. SBEM.
- Level 4 — buildings with mechanical ventilation, comfort cooling or full air conditioning. Still SBEM.
- Level 5 — the most complex or innovative buildings: atria and light wells, automatic shading, extensive thermal mass, highly glazed or ventilated double-skin facades. These cannot be modelled reliably in a simplified tool and need Dynamic Simulation Modelling.
If your building has an atrium, tell us at the quote stage, not after.
England, Wales and Scotland
England: Approved Document L Volume 2, 2021 edition. The 2026 edition is published and takes effect on 24 March 2027 (24 September 2027 for higher-risk buildings), with transitional arrangements for work already notified. Projects in design now need to know which edition they will be judged against — ask us.
Wales: its own Approved Document L Volume 2 (2022 edition, in force 29 March 2023) with the same four metrics. Wales’s consequential-improvements duty is broader than England’s — it is not limited to buildings over 1,000 m².
Scotland: not Part L at all. The route is Section 6 (Energy) of the Building Standards Technical Handbook (Non-domestic), which sets its own Target Emissions Rate — but the calculation tool is still SBEM, run to Scotland’s own NCM modelling guide.
Where commercial buildings fail, in our experience
Not regulation — just what we see. Lighting efficacy and controls in buildings where the lighting spec was left to the contractor. Glazing ratios on the elevation that faces the road. Heating and cooling plant chosen on capital cost before anyone modelled it. And the fabric U-value that was fine on the drawings until a product substitution. Each of them is a ten-minute fix at design stage and a very expensive one at completion.
How we work
It is a desktop assessment from your drawings and specification — no site visit. If the base calculation fails, we model the scenarios and recommend the most cost-effective route to a pass, working with your design team rather than just reporting a number. We price the SBEM and the EPC together.
Commercial projects usually need air tightness testing as well, and sometimes an environmental noise survey — we cover both, along with everything else in our services for commercial buildings. Get a quote or call 01202 623236.
Common questions
What is an SBEM calculation?
SBEM — the Simplified Building Energy Model — is the calculation tool within the National Calculation Methodology for buildings other than dwellings. It models the building's fabric, heating, cooling, lighting, ventilation and renewables and compares the result against a notional building of the same size and shape. Compliance with Part L is shown when the building's CO2 emission rate and primary energy rate both come in below their targets and the fabric and services meet the limiting standards. The output document Building Control receives is called a BRUKL.
When do I need an SBEM calculation?
For any new building that is not a dwelling and is heated or cooled — offices, retail, industrial units, schools, leisure, hotels, mixed-use commercial floors. A material change of use can also trigger it. Extensions are dealt with under the new-thermal-element rules rather than an automatic full calculation, and the regulations exempt places of worship, temporary buildings with a planned use of two years or less, low-energy-demand industrial and agricultural buildings, and stand-alone buildings under 50 m².
Do I need one SBEM or two?
Two. Regulation 27 requires a design-stage notice — with the target rate, the as-designed rate and the specification it depends on — before work starts, and an as-built notice within five days of completion showing the as-constructed rate and any changes to that specification. The as-built BRUKL is the one that gets forgotten and the one that holds up sign-off.
Is the commercial EPC part of the SBEM?
It comes from the same model but it is a separate legal duty. Under the Energy Performance of Buildings Regulations, an EPC must be given to the building owner within five days of the work completing and its reference number notified to the local authority. It has to be produced by an accredited non-domestic energy assessor. We do both from one model so the numbers agree.
When is SBEM not enough — when do I need dynamic simulation?
When the building is complex enough that a simplified model cannot represent it reliably: atria and light wells, automatic shading, extensive thermal mass, highly glazed facades, ventilated double-skin facades. Those need Dynamic Simulation Modelling and a Level 5 assessor. Simple naturally ventilated buildings are Level 3; mechanically ventilated or air-conditioned buildings are Level 4. The level sets the fee and the programme, so it is worth knowing early.
Does SBEM apply in Wales and Scotland?
Yes in both, under different documents. Wales uses its own Approved Document L Volume 2 (2022 edition, in force 29 March 2023) with the same four compliance metrics as England. Scotland does not use Part L at all — the route is Section 6 of the Building Standards Technical Handbook (Non-domestic) — but the calculation tool is still SBEM, run to Scotland's own NCM modelling guide.
Which edition of Part L applies to my project?
Today, the 2021 edition of Approved Document L Volume 2. The 2026 edition is published and takes effect on 24 March 2027 for most work (24 September 2027 for higher-risk buildings), with transitional arrangements for work already notified. A building being designed now needs to know which edition it will be assessed under, and we will tell you.