Part L of the Building
Regulations, explained.
Part L covers the conservation of fuel and power — how much energy a building uses and how much carbon it emits. This guide covers what it asks of you on site, what changed in the 2021 edition, and what the photographic evidence requirement means in practice.
What is Part L?
Part L of the Building Regulations is the section covering the conservation of fuel and power. It sets the energy efficiency standards a building has to meet, and it applies to both new buildings and work to existing ones. It is published as Approved Document L, in four volumes:
- Approved Document L, Volume 1: Dwellings — new and existing homes
- Approved Document L, Volume 2: Buildings other than dwellings — everything else
Compliance is not judged on the drawings alone. For new dwellings it is demonstrated through a SAP calculation at design stage, and then again as built, with the as-built submission backed by evidence that what was designed is what was actually constructed.
That last point is what changed most in the 2021 edition, and it is where most of the day-to-day work now sits.
What changed in the 2021 Part L update
The 2021 edition of Approved Document L came into force in June 2022 and is often referred to as Part L 2021. It is the interim step towards the Future Homes Standard. Three changes matter most on site:
1. A step change in carbon targets. New dwellings are expected to produce substantially less CO₂ than under the previous edition — roughly a 31% reduction — which pushes up insulation standards, airtightness and the use of low-carbon heating.
2. The BREL report became mandatory. Compliance for new dwellings now runs through a Building Regulations England Part L report, signed at design stage and again as built.
3. Photographic evidence became mandatory. The as-built BREL report must be accompanied by a photographic record of the construction details that affect thermal performance, as set out in Appendix B of Approved Document L. This is the part that changed how sites actually work, because it needs someone to capture the right image at the right stage, before the detail is covered up.
The photographic evidence requirement
Appendix B sets out the construction details that need photographing. In broad terms:
- Foundations and ground floor — insulation at foundation edges and ground floor perimeters, and external door thresholds
- Walls — insulation continuity at floor-to-wall junctions, around structural penetrations, and at window and door reveals
- Roof — insulation at roof edges, eaves and any changes in level
- Airtightness — the sealing details that deliver the tested air permeability
- Building services — heating, hot water and ventilation plant, labelled and identifiable
One photograph per unique detail, per plot, with close-ups where a detail needs clarity. Images should be geolocated and carry a date and time stamp so the evidence can be tied to the right plot at the right stage.
The photographs go to the SAP assessor, who reviews them before completing the as-built SAP assessment and issuing the EPC. If the evidence is incomplete, that is where the build stalls.
Who is responsible for what
- The developer signs the design-stage BREL report before construction starts, confirming the design meets the requirements, and signs the as-built report at completion.
- The site team captures the photographic evidence as the work proceeds. It can be taken by anyone working on the project, though a named responsible person is better, because the record needs to be consistent.
- The SAP assessor reviews the evidence, completes the as-built SAP assessment and produces the EPC.
- Building control does not take the photographs. They are for the BREL and SAP process.
In practice the evidence is the bottleneck, because it has to be captured at the moment the detail is open and cannot be recreated afterwards.
Part L questions we get asked
When did Part L 2021 come into force?
The 2021 edition of Approved Document L came into force in June 2022, with transitional arrangements for work already underway. It applies to new dwellings and to work on existing buildings.
Is photographic evidence a legal requirement?
The photographic record is required as part of the as-built BREL report process set out in Approved Document L. Without it, the SAP assessor cannot complete the as-built assessment, and the EPC cannot be issued.
How many photographs are needed per plot?
At least one photograph for every unique construction detail on that property, plus close-ups wherever a detail needs more clarity. The number varies with the complexity of the build, but a typical dwelling runs to dozens of images.
What is the difference between Part L and the Future Homes Standard?
Part L 2021 is the current standard and an interim step. The Future Homes Standard is the next step, intended to make new homes zero carbon ready, with a further reduction in emissions and a move away from fossil fuel heating.
What happens if the evidence is incomplete?
The SAP assessor cannot sign off the as-built assessment, so the EPC is not issued and the plot cannot be completed. Because the details are covered up as the build progresses, missing images often cannot be recreated without opening work back up.
Capture the evidence as you build
AutoBREL gives each plot its own checklist of required details and tags every image with a time-stamp and location as it is taken.
- Per-plot checklists built around Appendix B
- Automatic geo-tagging and time-stamping
- Evidence your SAP assessor can review in one place
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