Finance Editor, Kael Tripton Ltd - LBS MBA - Verified against FCA Handbook: 14 June 2026
Quick answer
Part L of the Building Regulations (Approved Document L) sets energy efficiency standards for new and existing buildings in England. The 2022 update requires new homes to produce 30% fewer carbon emissions than 2013 standards. U-values for new dwellings: walls 0.18, floors 0.13, roofs 0.11 W/m2K. The Future Homes Standard (2025+) will require 75-80% fewer emissions.
What Is Part L of the Building Regulations and What Does It Require?
Direct answer
What does Part L of the Building Regulations cover?
Part L (Approved Document L, gov.uk) covers the conservation of fuel and power. The 2022 update requires new homes to produce 30% fewer carbon emissions than 2013 standards. Maximum U-values: walls 0.18, floors 0.13, roofs 0.11 W/m2K. SAP calculations are required to demonstrate compliance. The Future Homes Standard (2025+) will require 75-80% fewer emissions, effectively requiring low-carbon heating in all new homes.
Confirm which version of Part L applies
Part L 2021 Vol 1 (new dwellings, June 2022), Part L 2021 Vol 2 (existing dwellings/non-domestic). Check the approved document at gov.uk/government/publications/conservation-of-fuel-and-power-approved-document-l.
Instruct a qualified SAP assessor
SAP (Standard Assessment Procedure) is the methodology for demonstrating Part L compliance. A qualified SAP assessor runs the calculation and produces the compliance report.
Ensure fabric standards are met
Specify insulation to meet the U-value targets: walls 0.18, floors 0.13, roofs 0.11 W/m2K for new dwellings.
Commission an EPC on completion
A SAP-based Energy Performance Certificate (EPC) is required on completion of new dwellings and most extensions.
Get Building Control sign-off
Submit your SAP calculations to Building Control as part of the Part L compliance package before and after construction.
| Building element | Max U-value (new dwellings) | Max U-value (extensions) |
|---|---|---|
| External walls | 0.18 W/m2K | 0.18 W/m2K |
| Ground floors | 0.13 W/m2K | 0.15 W/m2K |
| Roofs | 0.11 W/m2K | 0.15 W/m2K |
| Windows/doors | 1.2 W/m2K | 1.4 W/m2K |
| Party walls | 0.0 W/m2K (no heat loss permitted) | N/A |
Frequently Asked Questions
What is Part L of the Building Regulations?
Part L of the Building Regulations (formally Approved Document L) covers the conservation of fuel and power. It sets minimum standards for the energy efficiency of new buildings and renovations in England. Part L was significantly updated in June 2022 (for new dwellings) and April 2023 (for existing dwellings and non-domestic buildings) as part of the Future Homes Standard pathway. The 2022 edition requires new homes to produce approximately 30% fewer carbon emissions than the previous 2013 standard.
What does Part L require for new homes?
Part L 2021 (effective June 2022 for new dwellings) sets primary energy rate targets, carbon emission rate targets and fabric efficiency standards. New homes must meet: a primary energy rate no greater than 100% of the target primary energy rate, a dwelling emission rate no greater than the target emission rate, and minimum fabric efficiency standards (U-values for walls, floors, roofs and windows). The new homes must also have a home energy model prepared by a qualified assessor.
What are U-values under Part L?
U-values measure the rate of heat loss through a building element (wall, floor, roof, window) in watts per square metre per degree Kelvin (W/m2K). Lower U-values mean better insulation. Part L sets maximum U-values for building elements. As of June 2022, typical maximum U-values for new dwellings: external walls 0.18 W/m2K, ground floors 0.13 W/m2K, roofs 0.11 W/m2K, windows 1.2 W/m2K. For extensions and existing buildings, different standards apply under Part L volume 2.
Does Part L apply to extensions?
Yes. Part L applies to extensions to existing dwellings, though the requirements are less stringent than for new build. Extensions must meet minimum fabric U-values and, if the extension increases the dwelling's floor area by more than 25%, a whole-building SAP calculation may be required. Conservatories are generally exempt from Part L if they are separated from the main dwelling by a wall, door or window.
What is the Future Homes Standard and how does it relate to Part L?
The Future Homes Standard (FHS) is the UK government's target for all new homes built from 2025 onwards to produce 75-80% fewer carbon emissions than homes built under 2013 regulations. Part L 2021 is an interim step towards the FHS. The government has confirmed the FHS will be implemented through a final update to Part L (and Part F for ventilation) expected to come into force for new dwellings. The FHS requires heat pumps or other low-carbon heating as the primary heat source, eliminating gas boilers from new homes.
Primary sources
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