Approved Document L - England
The Future Homes Standard was published on 24th March 2026. For more information on the Standard and its implementation timeline, please click here.
This page contains information on the current version of Part L for England, which will be replaced by the Future Homes Standard when it is implemented.
On 15th June 2022, a revised version of Part L to the Building Regulations came into force in England. This is supported by new ADL (ADL 2021).
Guidance on the ADLs for the existing version of Part L to the Building Regulations (ADL 2013) is retained at the bottom of this page for reference. This guidance will only apply to individual units where plans have been submitted by 14th June 2022 and work on the unit has commenced by 14th June 2023.
ADL 2021 – Came into force 15th June 2022
There are two Approved Documents L:
Approved Document L, Conservation of fuel and power, Volume 1: Dwellings (ADL1)
Approved Document L, Conservation of fuel and power, Volume 2: Buildings other than dwellings (ADL2)
Each document sets out what, in ordinary circumstances, may be accepted as reasonable provision for compliance with the energy efficiency requirements of the Building Regulations for the type of building work in question.
New buildings
The Approved Documents include a number of key metrics which all new build dwellings and non-domestic buildings must meet. These are:
- Primary Energy – which considers both the energy used within the building, and the energy used in upstream activities to prepare the fuel.
- Carbon Emissions – which sets the maximum expected operational carbon emissions from a building.
- Fabric Energy Efficiency Standards (FEES) (domestic only) – which sets the target fabric performance for the property and is affected by U-values, airtightness, thermal mass, thermal bridging and internal and solar gains within the property.
- Worst-case U-values (area weighted) – which set the worst possible U-values that walls, floors and roofs can achieve on average across their total area.
The targets for Primary Energy and Carbon Emissions are set via modelling software (e.g. SAP for domestic, SBEM for non-domestic). An energy assessor inputs the building dimensions into the software. The software will then apply a set Notional Dwelling / Building specification to a theoretical building of the same dimensions. From this, it generates the performance targets that the actual building and building specification are compared against.
The Notional Building specification for non-domestic properties varies depending on whether the space is used for side-lit, top-lit or un-lit activities. This is in reference to natural lighting within a space. Spaces for side-lit activities will primarily use windows for daylighting – this includes offices, schools, healthcare facilities etc. Spaces which are top-lit will typically include warehouses and distribution centres, where there are minimal or no heat demands, so the building fabric has less of an impact on overall energy demands.
Project teams are free to diverge from the Notional Dwelling / Building specification providing they meet the key metrics outlined above. In many cases, however, they form the starting point for building fabric specifications.
The fabric values from the Notional Dwelling / Building specifications, and worst-case U-values are shown in the tables below.
Domestic
Element type | Notional Dwelling (W/m2K) | Area weighted worst case U-values (W/m2K) |
|---|---|---|
Wall | 0.18 | 0.26 |
Floor | 0.13 | 0.18 |
Roof | 0.11 | 0.16 |
Non-domestic
Element type | Notional Building - side-lit and unlit activities (W/m2K) | Notional Building - top-lit activities (W/m2K) | Area weighted worst case U-values (W/m2K) |
|---|---|---|---|
Wall | 0.18 | 0.26 | 0.26 |
Floor | 0.15 | 0.22 (unless better uninsulated) | 0.18 |
Roof | 0.15 | 0.18 | 0.16 (pitched) / 0.18 (flat) |
Existing buildings
Certain works on existing buildings may also be covered by the requirements of ADL. The requirements vary depending on whether it is a new / replacement thermal element, a renovated element, an extension or a change of use.
Adding or replacing thermal elements
These apply where:
- a new thermal element is added (such as a dormer window); or
- a thermal element is replaced (such as a reroofing).
On these projects, thermal elements will typically be expected to meet, or improve on, the area weighted average maximum U-values shown in the table below.
Element type | Domestic - maximum U-value (W/m2K) | Non-domestic - maximum U-value (W/m2K) |
|---|---|---|
Wall | 0.18 | 0.26 |
Floor | 0.18 | 0.18 |
Roof | 0.15 | 0.16 (pitched) / 0.18 (flat) |
As these are area weighted average U-values, it is possible to insulate certain areas of an element to worse U-values, provided this is compensated for elsewhere in the construction. In all cases, the U-values should be no worse than the limiting U-values (0.70 W/m2K - walls and floors, 0.35 W/m2K – roofs). Some additional flexibility is also given for certain defined scenarios, such as where fitting floor insulation may create an access problem.
Consequential Improvements may also apply to the existing buildings with a useable floor area over 1000 m2 depending on the type of work being carried out (typically for extensions).
See the relevant Approved Document for further details on Consequential Improvements and design flexibility options.
Renovated elements
Separate improved U-values are applied when undertaking certain renovation works on an existing thermal element. These renovation works include:
- fitting a new layer of cladding or render on the outside of a thermal element;
- drylining the internal surface of a thermal element;
- stripping down a thermal element to the basic structural components then rebuilding;
- replacing the waterproof membrane on a flat roof;
- adding cavity wall insulation; and
- where more than 50% of the surface of an individual element is renovated (for example, by applying cladding, render or a waterproof membrane), or more than 25% of the surface area of the external envelope is renovated (for example, by fitting drylining).
Ideally, this work should look to achieve the Improved U-values shown in the table below as a minimum. Where this isn’t technically feasible, or will not provide payback within 15 years, you should look to achieve the best possible U-values which are achievable. In all cases, you should reach, or improve upon, the 'Threshold U-values' shown below.
Element type | Improved U-values - domestic - area-weighted average (W/m2K) | Improved U-values - non-domestic - area-weighted average (W/m2K) | Threshold U-values for retained fabric (W/m2K) |
|---|---|---|---|
Pitched roof - insulated at ceiling level | 0.16 | 0.16 | 0.35 |
Pitched roof - insulated at rafter level | 0.16 | 0.18 | 0.35 |
Flat roof or roof with integral insulation | 0.16 | 0.18 | 0.35 |
Wall - cavity insulation | 0.55 | 0.55 | 0.70 |
Wall - internal or external insulation | 0.30 | 0.30 | 0.70 |
Floor | 0.25 | 0.25 | 0.70 |
Building an extension
When constructing an extension, all new elements will need to meet the requirements for adding and replacing thermal elements whilst any refurbished thermal elements will need to meet those for renovated thermal elements.
To provide some flexibility, the U-values for the individual elements can be area weighted. This means it is possible to build some to a lower fabric standard, providing the area weighted U-value of all the elements added together is no greater than for a notional extension of the same dimensions as the actual one, which uses the U-values for adding or replacing thermal elements.
If even greater design flexibility is needed, then project teams can calculate the expected carbon emission rate from the dwelling or building with its notional extension. They can then use SAP to prove the that the predicted carbon emissions rate from the dwelling or building and the extension is no higher than for the notional version. If, as part of achieving this, upgrades are proposed to the existing dwelling or building, these should be no worse than the improved U-values for renovated elements.
As mentioned above, if the floor area of the building is over 1000 m2, then any extension will also trigger consequential improvements to raise the energy efficiency for the whole building. See the relevant Approved Document for further details.
Change of use or energy status
When a building or a section of a building is subject to a change of use (e.g. from office to apartments) or to a change in energy status (e.g. where a loft or garage is converted to become part of the heated building) then the elements within this space must meet the requirements for adding or replacing thermal elements or renovating thermal elements as is appropriate for the work.
Where design flexibility is required, reasonable provision would be to use SAP to demonstrate that the calculated carbon dioxide emission rate from all the dwellings in the building, as it will become, is no greater than if each dwelling had been improved following the guidance above.
CPD training for Part L
Our suite of CPD training presentations can be delivered in-person or virtually. CPDs are available for Section 6 Scotland, as well as Part L England and Part L Wales, covering new and existing dwellings and buildings.
U-value calculator
Try our free online U-value calculator to calculate the thickness of material needed to meet the new levels of thermal performance. With a number of roof, wall and floor constructions, the calculator is quick and easy to use.
ADL 2013 - Discontinued from 15th June 2022
There are four Approved Documents L:
Approved Document L1A: Conservation of fuel & power in new dwellings (ADL1A)
Approved Document L1B: Conservation of fuel & power in existing dwellings (ADL1B)
Approved Document L2A: Conservation of fuel & power in new buildings other than dwellings (ADL2A)
Each document sets out what, in ordinary circumstances, may be accepted as reasonable provision for compliance with the energy efficiency requirements of the Building Regulations for the type of building work in question.
Please note – this guidance can only be used where plans were submitted by 14th June 2022 and work on the individual unit commenced by 14th June 2023.
Domestic
Element type | Notional Dwelling (W/m2K) | Existing building - extension (W/m2K) | Existing building - refurbishment (W/m2K) |
|---|---|---|---|
Wall | 0.18 | 0.28 | 0.30 / 0.55* |
Floor | 0.13 | 0.22 | 0.25 |
Pitched roof - ceiling level | 0.13 | 0.16 | 0.16 |
Pitched roof - rafter level | 0.13 | 0.18 | 0.18 |
Flat roof | 0.13 | 0.18 | 0.18 |
* A U-value of 0.55 W/m2K is used for cavity insulation and 0.30 W/m2K for internal or external wall insulation.
Non-domestic
Element type | Notional Building W/m2K) | Existing buildings - extensions (W/m2K) | Existing buildings - refurbishment (W/m2K) |
|---|---|---|---|
Wall | 0.26 | 0.28 | 0.30 / 0.55* |
Floor | 0.22 | 0.22 | 0.25 |
Pitched roof - ceiling level | 0.18 | 0.16 | 0.16 |
Pitched roof - rafter level | 0.18 | 0.18 | 0.18 |
Flat roof | 0.18 | 0.18 | 0.18 |
* A U-value of 0.55 W/m2K is used for cavity insulation and 0.30 W/m2K for internal or external wall insulation.
Page updated 14/04/2026