Part L for Non-Domestic Buildings
Which energy calculations does your project need? Use our interactive guide to find out.
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Part L of the Building Regulations sets the energy efficiency standards that all non-domestic buildings in England must meet. Whether you’re constructing a new commercial building, extending an existing one, or carrying out a conversion, different types of work trigger different compliance requirements — from simple U-value calculations to a full SBEM calculation and BRUKL report. This interactive guide walks you through the decision process for each project type, helping you understand which calculations your project needs, which version of the regulations applies, and when you need professional energy assessment support.
Based on Approved Document L, Volume 2 (2021 edition with 2023 amendments) & previous Part L2A / L2B.
⚠ This is critical — get it wrong and your project won’t be signed off
The version of Part L your project must comply with depends on when your Building Regulations application was submitted (building notice, initial notice, or full plans deposit) and when work commenced on each individual building. It is not based on the planning permission date. Different buildings on the same site can fall under different versions of the regulations.
📅 Transitional Arrangements Timeline (England — Non-Domestic)
If work did NOT commence by 15 June 2023 → you must use Part L 2021 (Volume 2) instead, regardless of when you applied.
This remains in force until the Future Buildings Standard comes into effect (expected ~2026/27).
Exact dates to be confirmed — check GOV.UK for the latest.
| Building Regs Application Date | Work Commenced By | Version to Use | Calc Tool |
|---|---|---|---|
| Before 6 April 2014 | Before 6 April 2015 | Part L2A / L2B 2010 | SBEM v4 |
| 6 April 2014 – 14 June 2022 | Before 15 June 2023 | Part L2A / L2B 2013 | SBEM v5 |
| Before 15 June 2022 | NOT commenced by 15 June 2023 | Part L Vol 2 (2021) ← | SBEM v6 |
| 15 June 2022 onwards | Any time (current) | Part L Vol 2 (2021) ✓ | SBEM v6 / DSM |
| After FBS in-force date (expected ~2026/27) | Subject to transition | Future Buildings Standard | Updated SBEM / DSM |
⚠ Common mistakes to avoid
- Planning permission date ≠ Building Regs application date. It’s the Building Regs application (building notice, initial notice, or full plans) that counts.
- Transitional provisions apply per individual building — not per site or per planning application. On a phased development, early buildings may use one version while later ones must use the next.
- “Commenced” under Part L 2021 transitions means excavation for foundations, piling, or drainage specific to that building — not just site-wide enabling works.
Hover over any term for a definition
BRUKL Report · SBEM · DSM · Area-Weighted U-Value Calc · EPC · Elemental Compliance
BER · TER · BPER · TPER
Exempt buildings include:
- Places of worship
- Temporary buildings used for ≤2 years
- Stand-alone buildings under 50 m² total floor area
- Industrial sites, workshops & non-residential agricultural buildings with low energy demand
- Some buildings protected under heritage / listed-building legislation where compliance would unacceptably alter character
No BRUKL, SBEM or EPC is required. Normal good-practice insulation still recommended.
You need a full energy model
- Design-stage BRUKL — submitted to Building Control before work starts
- As-built BRUKL — submitted after completion, reflecting actual specifications & air test result
- EPC — lodged on the national register
The BRUKL must show: BER ≤ TER, BPER ≤ TPER, fabric meets minimum area-weighted U-values, and solar gain limits are satisfied (Criterion 3).
Which software?
SBEM (Simplified Building Energy Model) is used for most standard buildings. For complex buildings with atria, advanced natural ventilation, mixed-mode cooling, or bespoke systems, Dynamic Simulation Modelling (DSM) such as IES-VE or DesignBuilder should be used instead. Both produce the same BRUKL output document.
“Large extension” — treated like a new build
The extension must meet full Part L new-build standards (BER ≤ TER, BPER ≤ TPER). Design-stage and as-built BRUKL reports required, plus an EPC. The model covers the extension only (but may reference the host building’s heating plant).
“Smaller extension” — simpler compliance
No full SBEM/BRUKL needed. Instead, follow the steps below ↓
Glazing limits (Table 10.1 summary)
The total window/door/rooflight area must not exceed a set % of the extension’s exposed façade, varying by building type. For example: offices & retail ~40% of façade, warehouses ~15%, etc. Display windows, smoke vents & vehicle doors are excluded from the count.
Meet individual U-values
Provide U-value calculations for each element (walls, roof, floor, windows) meeting the limiting values in Table 4.1. Also meet minimum building services efficiency standards.
No SBEM or BRUKL required.
Trade off between elements
Show that the overall area-weighted U-value of the extension is no worse than a “notional” extension of the same shape with compliant glazing and minimum U-values. Improve insulation elsewhere to compensate for extra glazing.
No SBEM needed — a spreadsheet-style calculation suffices.
Use SBEM to prove it works
If the extension can’t pass via elemental or area-weighted methods (e.g. very heavily glazed), a full SBEM calculation can model the extension and demonstrate compliance through the BER/TER route. A BRUKL report is produced.
A “material change of use” under Regulation 5 triggers Part L requirements. This includes converting a building previously exempt (e.g. agricultural) into regulated use (e.g. office), or converting domestic to non-domestic use.
Full SBEM calculation required
- Thermal elements (walls, floors, roof, windows) must be upgraded to meet minimum standards
- SBEM demonstrates the upgraded fabric & services meet requirements
- Design-stage and as-built BRUKL reports needed
- An EPC must be produced
Note: The SBEM for a conversion checks thermal improvements — it’s slightly different from a new-build assessment but still produces a BRUKL.
Assess each element being changed
If you’re just changing the use but not doing significant physical work, you may only need to demonstrate the existing fabric meets reasonable standards. If substantial renovation accompanies the change, see Section 4 below.
Meet Table 4.1 standards
New/replacement walls, roofs, floors must meet the “new element” U-value limits. Replacement windows must meet limiting standards. Provide U-value calculations for each element. No SBEM required.
Upgrade to renovation standards
If renovating >50% of a thermal element or >25% of the building envelope, the whole element must be upgraded to at least the renovation U-value. Provide calculations. No SBEM needed.
First fit-out / large HVAC (>1000 m²)
First fit-out of a shell-and-core building requires SBEM + BRUKL for the fitted-out zones. Major HVAC replacements in large buildings (>1000 m²) increasing system capacity may also trigger an SBEM assessment.
💡 Consequential improvements
For existing non-domestic buildings over 1,000 m², when extending or increasing HVAC capacity, you may also be required to make “consequential improvements” to the rest of the building — e.g. upgrading boiler controls, improving insulation, or replacing old lighting. These are checked by Building Control as part of the approval process.
No energy calculations required. The conservatory/porch is treated as an unheated space outside the thermal envelope.
Follow the extension routes in Section 2 above. No glazing area limits apply, but elements must meet minimum U-values and overall performance must be demonstrated.
| Type of Work | BRUKL Report? | SBEM / DSM? | Area-Weighted U-Value? | Individual U-Value Calcs? | EPC? |
|---|---|---|---|---|---|
| New build | Yes ✓ | Yes ✓ | Within SBEM | Yes ✓ | Yes ✓ |
| Large extension (>100 m² AND >25% existing area) | Yes ✓ | Yes ✓ | Within SBEM | Yes ✓ | Yes ✓ |
| Small extension — within glazing limits | No | No | No | Yes ✓ | Maybe* |
| Small extension — over glazing limits | No | No | Yes ✓ | Yes ✓ | Maybe* |
| Conversion / change of use | Yes ✓ | Yes ✓ | Within SBEM | Yes ✓ | Yes ✓ |
| Renovation of thermal elements | No | No | No | Yes ✓ | No |
| Shell fit-out / major HVAC | Yes ✓ | Yes ✓ | Within SBEM | Yes ✓ | Yes ✓ |
* An EPC may be needed if the building is being sold or let, regardless of the type of work.
Need Help With Your Part L Calculations?
Our dedicated technical team handles BRUKL calculations for new builds, extensions, conversions, and fit-outs across London and the UK. Call us or request a free quote.
What Is a BRUKL Report?
A BRUKL (Building Regulations UK Part L) report is the standardised output document from an SBEM or Dynamic Simulation Model calculation. It proves to Building Control that your non-domestic building meets the energy performance requirements of Part L of the Building Regulations.
For new builds and large extensions, you need both a design-stage BRUKL (submitted before work begins) and an as-built BRUKL (submitted after completion, reflecting the actual specifications and air permeability test result). The report shows whether the Building Emission Rate (BER) is below the Target Emission Rate (TER) and whether the Building Primary Energy Rate (BPER) is below the Target Primary Energy Rate (TPER).
Without a compliant BRUKL, Building Control will not sign off your project. Learn more about our BRUKL calculations service.
SBEM vs DesignBuilder — Which Do You Need?
Most non-domestic buildings can be assessed using SBEM (Simplified Building Energy Model), the government’s free calculation tool. However, for complex buildings with features like atria, mixed-mode ventilation, advanced natural ventilation strategies, or bespoke HVAC systems, Dynamic Simulation Modelling (DSM) using software like DesignBuilder or IES-VE is required.
Easy EPC uses DesignBuilder for all our commercial EPC assessments — not the basic iSBEM interface that many assessors rely on. DesignBuilder creates a full 3D energy model of your building, giving more accurate results and allowing us to optimise your design to achieve the best possible rating. This matters because a more accurate model can identify energy savings that a simplified approach would miss.
How Easy EPC Can Help
Whether your project needs a design-stage BRUKL, an as-built assessment, or you’re unsure which calculations apply, our dedicated technical team can help. We use DesignBuilder — the market-leading 3D energy modelling platform — for all our non-domestic energy assessments, giving you more accurate results than the basic iSBEM tools many assessors rely on.
Our in-house specialists handle BRUKL calculations for new builds, extensions, conversions, and shell fit-outs across London and the rest of the UK. We also provide commercial EPCs, MEES consultation, and Display Energy Certificates.
Part L & BRUKL — Frequently Asked Questions
You need a BRUKL for any new non-domestic building, large extension (over 100 m² AND over 25% of existing floor area), conversion/change of use, or first fit-out of a shell-and-core building. Small extensions and thermal element replacements typically only need U-value calculations.
This depends on when your Building Regulations application was submitted — not your planning permission date. Projects with applications submitted on or after 15 June 2022 must comply with Part L Volume 2 (2021 edition) using SBEM v6. See our flowchart above for the full transitional arrangements.
Only if the extension is both over 100 m² AND over 25% of the existing building's floor area — this is classed as a "large extension" and needs a full SBEM/BRUKL. Smaller extensions only need individual U-value calculations, or an area-weighted U-value calculation if glazing exceeds the limits.
SBEM is the government's simplified calculation tool suitable for most standard buildings. DesignBuilder is a professional Dynamic Simulation Modelling (DSM) tool that creates detailed 3D energy models — required for complex buildings and recommended for any project where accuracy matters. Easy EPC uses DesignBuilder for all assessments.
Building Control will not issue a completion certificate without a compliant as-built BRUKL where one is required. This can delay or prevent occupation, sale, or letting of the building. Retrospective compliance is possible but often more expensive and complicated.
The Future Buildings Standard is expected to become law around 2026/27, with a 12-month transition period. It will require significantly lower carbon emissions from non-domestic buildings. Projects submitted before the in-force date will be able to use current Part L 2021 standards during the transition.
Ready to Get Started?
Tell us about your project and we’ll provide a clear quote for your BRUKL calculations or commercial EPC — usually within a couple of hours during office hours.