Part L 2026 is the 2026 edition of Approved Document L, published on 24 March 2026 and in force in England from 24 March 2027. It adds requirement L3: a new home needs on-site renewable electricity with an annual output at least equal to a PV array of 0.22 kWp/m² covering 40% of its ground floor area, which is about 3.74 kWp for a 42.5 m² ground floor.
What Part L 2026 changes
The Building Regulations are the legal minimum standard for building work in England, and Part L sets the energy and carbon rules. The 2026 edition of Approved Document L is titled Energy and greenhouse gas emissions. Volume 1 covers dwellings under three requirements:
- Requirement L1: conservation of fuel and power and minimisation of greenhouse gas emissions in buildings (fabric, building services and the energy targets).
- Requirement L2: on-site generation of electricity. Where generation or storage is installed it should be sized for the site, commissioned to the manufacturer's instructions and controllable without user intervention.
- Requirement L3 (new): renewable electricity generation for new dwellings and buildings containing dwellings. This is the requirement that makes solar PV standard on new homes.
Part L 2026 is designed to deliver homes with 75% lower carbon emissions than homes built to 2013 standards. Combined with low-carbon heating, it is the change the industry calls the Future Homes Standard.
Requirement L3: how much solar PV Part L 2026 expects
Paragraph 5.73 of the Approved Document says roof-mounted PV on a new house should achieve a reasonable output in one of two ways:
- The 40% reference array. An annual output, calculated with the approved methodology, at least equal to a PV array with an installed peak power of 0.22 kWp per m² over an area equivalent to 40% of the house's ground floor area, orientated south-east to south-west, at a 45° pitch and not overshaded.
- The practicable roof route. An annual output at least equal to an array covering the reasonably practicable roof area at 0.22 kWp/m².
Equation 5.1 turns the first route into a target: installed peak power = the area for PV panels (at least 40% of the ground floor area) × a panel efficiency of 0.22 kWp/m² or higher. The Approved Document notes that 0.22 kWp/m² is the same as 1 kWp for every 4.5 m² of panel.
| Ground floor area | 40% reference area | Reference array (0.22 kWp/m²) |
|---|---|---|
| 32 m² | 12.8 m² | 2.82 kWp |
| 42.5 m² | 17 m² | 3.74 kWp |
| 50 m² | 20 m² | 4.40 kWp |
| 65 m² | 26 m² | 5.72 kWp |
| 80 m² | 32 m² | 7.04 kWp |
Arithmetic from equation 5.1 of Approved Document L 2026, Volume 1. The reference array sets an output target; a real array on a different orientation or pitch may need to be larger or smaller to match it.
Three details catch designers out. First, the target is an annual output, not a panel count, so an east-west roof or a shallow pitch usually needs more panels than the reference. Second, the calculation has to use the same version of the approved methodology as the dwelling emission and primary energy rates (paragraph 5.72). Third, the panels do not have to go on the roof: paragraph 5.71 allows renewable technologies within the curtilage of the building, which can help on a shaded plot.
Flats and apartment buildings
For a building containing one or more dwellings, paragraph 5.74 applies the same 40% reference to the building's ground floor area, to each dwelling's share of it, or to the reasonably practicable roof area. For a multi-storey building, equation 5.2 takes the ground floor area as the total floor area divided by the number of storeys, and equation 5.3 allocates each flat a share in proportion to its floor area. On a tall block the practicable roof area is often the limiting factor, which is why the roof route matters for flats.
The three targets: TER, TPER and TFEE
Under requirement L1, the actual dwelling is compared with a notional dwelling of the same size and shape. Paragraph 1.4 of the Approved Document describes the notional dwelling's performance with three metrics:
- Target primary energy rate (TPER), in kWhPE/m² per year, influenced by the fabric and the fuel.
- Target emission rate (TER), in kgCO₂/m² per year, influenced by the fabric and the fuel.
- Target fabric energy efficiency rate (TFEE), in kWh/m² per year, influenced by the fabric only.
The notional dwelling's specification is set out in the SAP 10.3 specification (Appendix R) and, for the Home Energy Model, in the Future Homes Standard 2026 dwelling notional buildings tables.
SAP 10.3 or the Home Energy Model?
The Approved Document names two approved methodologies for new dwellings: the Home Energy Model (HEM) and the Standard Assessment Procedure. Their periods of validity are set in the Notice of Approval published on gov.uk. HEM's launch was postponed in June 2026, so SAP 10.3 is the methodology in use at launch. Whichever is used, the L3 renewable-output calculation must use the same version as the rest of the compliance calculation.
When does it apply? The transitional rules
Building Circular 01/2026 sets out the dates. The changes take effect on 24 March 2027 for building work that is not higher-risk building work. They do not apply where a building notice, initial notice or full plans application was given to the building control body before 24 March 2027, provided the work on that building starts before 24 March 2028. Protection is assessed building by building, so on a phased site some plots can fall inside it and others outside.
For higher-risk building work the changes take effect on 24 September 2027, and they do not apply where a valid building control approval application was submitted to the Building Safety Regulator before that date and has not been rejected.
Where does it apply?
The 2026 edition of Approved Document L and Circular 01/2026 apply in England. Wales has published its own Approved Document L (2026), so check the Welsh Government's guidance for its dates. Scotland sets its own building standards; its New Build Heat Standard has required zero direct emissions heating in most new buildings since April 2024.
Practical compliance pathway
For a developer or self-builder delivering new homes under Part L 2026, the practical sequence runs:
- Design stage: house types updated for fabric performance, a heat pump or heat network, and a PV array sized to the L3 output target.
- Compliance modelling: an accredited energy assessor runs SAP 10.3 to show the dwelling meets its TER, TPER and TFEE, and that the PV meets the L3 output.
- Building control: full plans application, building notice or initial notice, with the design-stage calculation.
- Site delivery: fabric built to the design values, an air permeability test on completion, the PV and heat pump commissioned to the manufacturers' instructions.
- As-built calculation: the SAP calculation updated with as-built values and the EPC issued.
- Sign-off: the completion certificate issued, with the MCS certificate and system documents in the homeowner's handover pack.
The SAP and HEM modelling guide covers steps 2 and 5 in more detail, and the 40% PV rule explainer works through array sizing on awkward roofs. To size a plot quickly, use the FHS PV calculator. For the other building regulations that apply to solar, from roof strength to electrical safety, see solar panels and building regulations, and for the tax position see VAT on solar panels.