Introduction to Part L Building Regulations: What It Covers and Why It Matters

Building regulations exist to make sure buildings are safe, efficient and sustainable. Among them, Part L stands out as the part focused on the conservation of fuel and power — in other words, how much energy a building uses and how much carbon it emits.

What Part L covers

Part L is published as Approved Document L, in two volumes: one for dwellings and one for buildings other than dwellings. It sets the energy efficiency standards a building must meet, covering:

• Fabric performance — U-values for walls, floors, roofs, windows and doors
• Thermal bridging — the junctions where heat escapes between elements
• Airtightness — how much uncontrolled air leakage the building allows
• Building services — the efficiency of heating, hot water, ventilation and lighting
• Carbon and primary energy — the resulting emission and energy rates

For a new dwelling, compliance is demonstrated through a SAP calculation at design stage, and then again as built.

What changed in the 2021 edition

The 2021 edition of Approved Document L came into force in June 2022. It is the interim step towards the Future Homes Standard, and it brought three changes that reshaped how sites work.

Tighter carbon targets. New dwellings are expected to produce around 31% less CO₂ than under the previous edition. That pushes up insulation standards, tightens airtightness targets and makes low-carbon heating far more common.

The BREL report. Compliance now runs through a Building Regulations England Part L report, signed by the developer at design stage and again as built.

Mandatory photographic evidence. The as-built BREL report has to be accompanied by a photographic record of the construction details that affect thermal performance, as set out in Appendix B.

Why the evidence requirement is the hard part

The first two changes are largely a design and specification exercise. The third is an operational one, and it lands on the site team.

The photographs have to be taken at the right stage, while each detail is still visible. Once insulation is boarded over or a junction is closed up, the evidence cannot be recreated without opening the work back up. A missing photograph at plot level can hold up the EPC and therefore completion.

That is why so many builders have found that the regulations themselves were the easy part, and keeping a consistent photographic record across every plot on every site is the thing that actually needed solving.

Where to go next

• Part L Building Regulations: a practical guide
• What is a BREL report?
• The photographic evidence requirements in full