Free tool
Part L 2021 vs 2026 comparison
Who runs your contract
Awais Sarwar, MSc — Accredited Energy Assessor
Awais is an accredited domestic and commercial energy assessor and the owner of Team EPC Ltd, which trades as Part L Consultant. He has surveyed and lodged EPCs across flats, houses, HMOs, managed portfolios and commercial premises throughout London and the Home Counties, and is currently studying an MSc in philosophy alongside running the business.
Off the clock: cricket, family time, an MSc in philosophy in progress and finding London's best food.
Awais Sarwar
Founder · Accredited energy assessor
Last reviewed 2026-09-15
Part L 2021 — the current standard
- In force in England
- 15 June 2022
- The transitional period for schemes notified under the previous standard ended on 15 June 2023.
- The Building Regulations etc. (Amendment) (England) Regulations 2021 (SI 2021/1391)Conservation of fuel and power: Approved Document L (2021 editions)
- Carbon reduction for new dwellings
- Around 31% below Part L 2013
- Conservation of fuel and power: Approved Document L (2021 editions)
- Dwelling metrics
- DER against TER, DPER against TPER, DFEE against TFEE, plus limiting fabric and services standards
- Conservation of fuel and power: Approved Document L (2021 editions)
- Non-domestic test
- Building Emission Rate and Building Primary Energy Rate against their targets, output as a BRUKL report
- Calculated with SBEM or approved dynamic simulation software.
- Conservation of fuel and power: Approved Document L (2021 editions)
- Design stage
- Calculation and BREL report submitted to the building control body before work starts
- Conservation of fuel and power: Approved Document L (2021 editions)
- At completion
- As-built calculation, air tightness test results, commissioning records and photographic evidence of key construction details
- Conservation of fuel and power: Approved Document L (2021 editions)
- On-construction EPC
- Required for every new dwelling, produced from the as-built calculation
- Conservation of fuel and power: Approved Document L (2021 editions)
- Extension glazing threshold
- 25% of the extension's floor area, plus the area of any windows or doors no longer in place
- Above that, the extension must be shown to perform no worse than a compliant one, normally through a SAP comparison.
- Conservation of fuel and power: Approved Document L (2021 editions)
Anything we cannot cite to a published document is left out of this comparison deliberately, including widely quoted carbon-reduction headlines for 2026 that are not yet confirmed in the Approved Documents.
Background
Reading the two standards side by side
Part L 2021 has been in force in England since 15 June 2022 and tests new dwellings on emissions, primary energy and fabric energy efficiency against targets, with limiting standards for fabric and services underneath. Non-domestic buildings are tested on emission and primary energy rates, output as a BRUKL report.
Part L 2026 keeps that structure and adds to it. The Regulations reframe Part L around greenhouse gas emissions as well as energy, introduce functional requirement L3 for on-site renewable electricity generation, bring lifts and escalators into fixed building services in new buildings, and add a duty to give information to new-home owners.
Everything on this page carries its source. The 2026 documents were revised on 8 September 2026 to correct minor errors, so always work from the current versions on GOV.UK rather than a downloaded copy.
Also useful
The other Part L tools
Part L 2026 transition checker
Enter your building control application date and your start on site, and see whether that building keeps transitional protection under the published 2026 dates.
Design-stage information checklist
Build a tailored list of the drawings, specification and services information a design-stage SAP or SBEM calculation needs for your project type.
Extension glazing area check
Enter your extension's floor area, its new glazing and the openings it removes, and see whether it stays inside the 25% allowance or needs a calculation.
Part L fee guide
Pick your project type and scale for the guide fee band we quote from, and what the fee does and does not include. Every job gets a written quote.
