Energy Efficiency in Buildings: A Guide to Part L

Approved Document L (Conservation of Fuel and Power) sets energy efficiency standards for buildings in England. It has four volumes: L Volume 1 (new dwellings), L Volume 2 (existing dwellings), L Volume 3 (new non-domestic), L Volume 4 (existing non-domestic). The 2022 edition requires a 31% improvement in energy efficiency over 2013 standards for new dwellings.

Key Performance Metrics

• Target Emission Rate (TER) / Dwelling Emission Rate (DER): CO₂ emissions – DER must not exceed TER
• Target Primary Energy Rate (TPER) / Dwelling Primary Energy Rate (DPER): Accounts for upstream energy losses – introduced in 2022
• Fabric Energy Efficiency Standard (FEES): Caps energy demand from space heating and cooling in kWh/m²/year

Minimum Fabric Standards for New Dwellings

• External walls: maximum 0.26 W/m²K
• Roofs: maximum 0.16 W/m²K
• Ground floors: maximum 0.18 W/m²K
• Windows: maximum 1.6 W/m²K (whole window)
• External doors: maximum 1.4 W/m²K
• Air permeability: tested, maximum 10 m³/(h·m²) at 50 Pa

Heating Systems

Gas boilers are not yet banned but are difficult to comply with. Air source heat pumps (CoP 2.5–3.5), ground source heat pumps (CoP 3.5–4.5+), district heating, and PV solar panels help meet the Target Emission Rate. The Future Homes Standard (expected 2025–2026) will effectively require heat pumps in new homes.

Extensions to Existing Dwellings

The new extension must meet minimum U-value standards. Replacement windows in existing dwellings must achieve maximum 1.6 W/m²K or Window Energy Rating C or better.

Ask the AI Copilot about Part L requirements for your project →