Approved Document L Volume 1: Dwellings (2021 Edition with 2023 Amendments) – Conservation of Fuel and Power
Approved Document L, Volume 1: Dwellings provides statutory guidance for complying with Part L of Schedule 1 to the Building Regulations 2010 in England. Issued by HM Government, this 2021 edition incorporates the 2023 amendments and governs the conservation of fuel and power as well as the on-site generation of electricity in residential buildings. The document sits alongside Approved Document L, Volume 2, which addresses non-domestic buildings, and took full effect on 15 June 2022, with specific 2023 updates concerning district heat networks.
The scope of the document encompasses new-build dwellings and work carried out on existing residential units, including extensions, renovations, and material changes of use. It establishes a regulatory framework based on three primary metrics calculated via the Standard Assessment Procedure (SAP): the Target Primary Energy Rate, the Target Emission Rate, and the Target Fabric Energy Efficiency Rate. Key structural elements include detailed specifications for insulating fabric elements, minimum efficiencies for building services, and mandatory procedures for air permeability testing and system commissioning. It also introduces the requirement for the Building Regulations England Part L (BREL) report and photographic evidence to verify build quality.
Detailed sections below describe the specific performance thresholds for building fabric and services, alongside compliance pathways for renovation projects and new extensions. These standards apply to all types of dwelling work defined under Regulation 3, ensuring that residential construction meets contemporary energy efficiency requirements.
Energy Performance Metrics and SAP Calculations
New dwellings must demonstrate compliance by meeting or exceeding three performance targets calculated against a theoretical notional dwelling of identical size and shape. These calculations must be performed both at the design stage and upon completion of the works.
- Target Primary Energy Rate: The maximum primary energy use allowed for the dwelling in a year, expressed in kWhPE/m²/year.
- Target Emission Rate: The maximum CO₂ emission rate, influenced by both the building fabric and the fuel source.
- Target Fabric Energy Efficiency Rate: A metric influenced solely by the building fabric, measured in kWh/m²/year.
- Standard Assessment Procedure (SAP): The Government-approved methodology for assessing the energy rating of dwellings; currently SAP 10 is referenced for energy calculations.
Limiting Heat Gains and Losses
Section 4 sets out the limiting standards for the building fabric to minimize unwanted heat loss. These standards are defined by maximum U-values, which measure the thermal transmittance of building elements.
- New Dwelling U-values: Maximum thresholds include 0.26 W/(m²·K) for walls, 0.16 W/(m²·K) for roofs, and 1.6 W/(m²·K) for windows and doors.
- Airtightness: Every new dwelling must undergo a pressure test to ensure it meets the minimum standard for air permeability as defined in Table 4.1.
- Thermal Bridging: The building fabric must be constructed to limit heat transfer at junctions. Compliance is verified through on-site audits and photographic evidence taken during construction.
- Continuity of Insulation: Guidance requires that the insulation layer is robust and continuous, particularly at junctions between floors and walls or around openings like windows and doors.
Fixed Building Services Efficiency
Fixed building services, including heating, hot water, and lighting, must meet minimum efficiency standards and be equipped with effective controls to prevent energy waste.
- Gas-fired Heating: Wet heating systems in new dwellings must achieve a minimum efficiency of 92%.
- Heat Pump Systems: Space heating via heat pumps must have a minimum Coefficient of Performance (COP) of 3.0, while domestic hot water heating requires a minimum COP of 2.0.
- Lighting Efficiency: Internal light fittings must use lamps with a minimum luminous efficacy of 75 light source lumens per circuit-watt.
- Thermostatic Controls: Each room or heating zone must be provided with thermostatic room controls to independently adapt heating output.
Work to Existing Dwellings and Extensions
When extending or renovating an existing dwelling, new elements must generally meet higher thermal standards than those required for new-build projects to compensate for the existing building's performance.
- Extensions: New thermal elements in extensions must meet limiting U-values such as 0.18 W/(m²·K) for walls and 1.4 W/(m²·K) for windows.
- Renovating Elements: If more than 50% of a thermal element's surface area is renovated, the entire element should be upgraded to meet the improved U-values in Table 4.3.
- Material Change of Use: Conversion projects creating new dwellings must satisfy requirements for energy status, including upgrading existing windows if their U-value exceeds 3.30 W/(m²·K).
- Consequential Improvements: Dwellings with a total useful floor area over 1000m² may require additional energy efficiency improvements when adding an extension or new building services.
Compliance Documentation and Commissioning
The document specifies rigorous reporting procedures to ensure that the as-built dwelling matches the design-stage specifications.
- BREL Report: A Building Regulations England Part L compliance report must be signed by the assessor and developer, then provided to the homeowner.
- Commissioning: All fixed building services and on-site electricity generation systems must be tested and adjusted to ensure they produce the maximum reasonable energy efficiency.
- Home User Guide: For new dwellings, owners must receive a guide containing non-technical advice on operating ventilation, heating, and on-site generation systems.
Frequently Asked Questions
What is the minimum boiler efficiency for a new dwelling?
Gas-fired wet heating systems, such as radiators or underfloor heating, must have a minimum efficiency of 92% as defined in the Energy-Related Products (ErP) directive.
Are air pressure tests mandatory for all new houses?
Yes, an air pressure test must be carried out on every new dwelling to verify it meets the air permeability standards set out in Section 7.
What are the U-value requirements for a new extension's walls?
New thermal elements in an extension to an existing dwelling must meet a limiting U-value of 0.18 W/(m²·K).
What constitutes a major renovation under Part L?
A major renovation is defined in Regulation 35 as the renovation of a building where more than 25% of the surface area of the external building envelope undergoes renovation.
How much glazing is allowed in a dwelling extension?
The total area of windows, roof windows, and doors in an extension should generally not exceed 25% of the floor area of the extension plus the area of any existing openings that the extension covers.
What is the required luminous efficacy for new lighting?
Internal light fittings installed in new or existing dwellings must have lamps with a minimum luminous efficacy of 75 light source lumens per circuit-watt.
Does Approved Document L Volume 1 apply to historic buildings?
Listed buildings and those in conservation areas do not need to comply fully if the work would unacceptably alter the building's character or appearance, though they must comply to the extent that is reasonably practicable.
What information must be provided to a new homeowner?
The owner must receive a signed BREL report, photographic evidence of construction quality, a Home User Guide, and operating and maintenance instructions for all building services.
