Part L Overview: Conservation of Fuel and Power

What This Requirement Covers

Approved Document L sets out the requirements for the conservation of fuel and power in buildings. The 2021 edition (effective June 2022) introduced significant uplift in energy performance standards as an interim step towards the Future Homes Standard (expected 2025). Part L applies to all building work, including new buildings, extensions, renovations, and changes of use.

Key Requirements

Part L Structure

Approved Document L is divided into

1. Volume 1: New dwellings
2. Volume 2: Existing dwellings (including extensions and renovations)
3. Part L (Non-domestic): Conservation of fuel and power in non-domestic buildings (separate volume)

New Dwellings (Volume 1, 2021 Edition)

The 2021 edition requires a 31% reduction in carbon emissions compared to the previous 2013 standard

1. Target Fabric Energy Efficiency (TFEE): Maximum fabric energy demand calculated through SAP (Standard Assessment Procedure)
2. Target Emission Rate (TER): Maximum CO2 emissions calculated through SAP
3. Dwelling Emission Rate (DER): The actual calculated emissions must not exceed the TER
4. Dwelling Fabric Energy Efficiency (DFEE): Must not exceed the TFEE
5. Primary energy rate: The dwelling's primary energy consumption must not exceed the target

Limiting Fabric Standards (New Dwellings)

Minimum fabric performance (U-values and air permeability)

1. External walls: 0.26 W/m²K maximum
2. Party walls: 0.20 W/m²K maximum (calculated using the conventions in SAP)
3. Floor: 0.18 W/m²K maximum
4. Roof: 0.16 W/m²K maximum
5. Windows and doors: 1.6 W/m²K maximum (whole unit, including frame)
6. Air permeability: 8 m³/(h.m²) at 50 Pa maximum (tested by pressure test)
7. Swimming pool basins: 0.25 W/m²K maximum

Existing Dwellings (Volume 2)

When work is carried out on an existing dwelling, the new or replacement elements must meet minimum standards

1. Replacement windows: 1.4 W/m²K maximum
2. New extension walls: 0.28 W/m²K maximum
3. New extension roof: 0.16 W/m²K maximum
4. New extension floor: 0.22 W/m²K maximum
5. Replacement boiler: Minimum 92% ErP efficiency
6. Where technically and economically feasible, consequential improvements may be required for larger extensions

SAP and EPC

1. All new dwellings must have a SAP calculation carried out by an accredited assessor
2. An Energy Performance Certificate (EPC) must be produced and registered on the national register
3. The EPC rates the dwelling from A (most efficient) to G (least efficient)
4. EPCs are valid for 10 years

The Future Homes Standard

1. The Future Homes Standard is expected in 2025 and will require a 75-80% reduction in carbon emissions compared to the 2013 baseline
2. New homes will be expected to use low-carbon heating (heat pumps) and have very high fabric efficiency
3. The 2021 Part L is designed as a stepping stone to the Future Homes Standard

Practical Compliance Tips

1. Engage a SAP assessor at the design stage to model energy performance and identify the most cost-effective route to compliance
2. Consider the whole-building approach: fabric efficiency first, then efficient services, then renewable energy
3. Air tightness testing is mandatory for new dwellings; plan for it in the construction programme and budget
4. Thermal bridging at junctions (around windows, at corners, at eaves) significantly affects energy performance; use accredited construction details or calculate psi-values
5. Photograph insulation installation before it is concealed for Building Control evidence
6. Keep SAP worksheets, air tightness test results, and commissioning certificates for the building file
7. Prepare for the Future Homes Standard by specifying heat pump-ready designs now