What Is Part L?

Part L (Approved Document L) is the section of the Building Regulations for England that deals with the conservation of fuel and power. It sets minimum energy efficiency standards for new buildings, extensions, and renovation work, including insulation levels, heating system efficiency, airtightness, and lighting.

What Part L Requires

Part L sets target U-values for every element of the building fabric. For new-build dwellings, current targets include:

• External walls: 0.18 W/m²K
• Ground floors: 0.13 W/m²K
• Pitched roof (at ceiling level): 0.11 W/m²K
• Flat roofs: 0.13 W/m²K
• Windows: 1.2 W/m²K

Extensions and Existing Buildings

Extensions have slightly less stringent targets than new builds. For example, an extension wall must achieve 0.18 W/m²K and windows 1.4 W/m²K. When renovating existing buildings (replacing windows, re-roofing, adding insulation), the elements you replace or renovate must meet the “reasonable provision” standards in Part L.

The 2021 Update

Part L was significantly updated in June 2022 (often referred to as the “2021 update”), tightening U-value targets and introducing a new carbon emissions target that is approximately 31% lower than the previous standard. This is seen as a stepping stone towards the Future Homes Standard expected in 2025, which will require even higher levels of insulation and low-carbon heating.

Scotland, Wales, and Northern Ireland

Part L specifically applies to England. Scotland has Section 6 (Energy), Wales has its own Part L, and Northern Ireland has Part F (Conservation of Fuel and Power). The requirements are similar but not identical.