England’s 2026 Approved Document L introduces a future requirement for on-site renewable electricity when a dwelling or a building containing dwellings is erected. This is a project-classification and transition question as well as an energy-design question. The rule does not mean that every secondary dwelling or conversion automatically follows the new-dwelling route.
Know the requirement and its dates
The Building Regulations etc. (Amendment) (England) Regulations 2026 create a new functional requirement, L3, for on-site renewable electricity generation. The regulations generally come into force on March 24, 2027. Circular 01/2026 lists specified provisions that take effect for higher-risk building work and work to an existing higher-risk building on September 24, 2027. Both dates are subject to transition rules, including conditions tied to building-control notices or applications and commencement. Check the circular and regulations for the specific provision and project route before relying on a date.
Understand the output method
Approved Document L uses an annual electricity-output target, calculated through the approved methodology. For a new dwelling-house, the official FAQ explains the reference basis in paragraph 5.73(a): photovoltaic peak power of 0.22 kWp per square metre over an area equivalent to 40% of the dwelling-house’s ground-floor area, converted to annual output using SAP 10.3. That reference describes the output to be achieved; it is not a universal panel layout. Buildings containing dwellings use the applicable area measure in the relevant equation, so do not apply the single-house calculation without checking the document.
Paragraph 5.73(b) describes an alternative output method for a new dwelling-house: assess the photovoltaic array against the reasonably practicable roof area, using 0.22 kWp per square metre of that area and the approved annual-output calculation. The official FAQ says to consider roof surfaces including those that face north or are shaded; a lower expected yield on its own is unlikely to justify leaving an otherwise reasonably practicable area out. The developer is responsible for identifying the reasonably practicable roof area and justifying that assessment to the relevant building-control body. This is a separate method from the paragraph 5.73(a) reference area above, and does not prescribe a panel layout.
The system must also be considered against the site and available infrastructure. The FAQ identifies demand and distribution-network export limits among the relevant factors and discusses controls, testing, adjustment, and commissioning. The reference output alone does not establish that a design is appropriately sized or that a particular connection can accept exports.
Confirm the project’s path before design is fixed
For a proposed ADU or secondary dwelling, establish whether the work is in England, whether the regulated work is an erection of a dwelling or a building containing dwellings, and which transition provision applies. Record the building-control notice or application, its date, and the work’s commencement status. Ask the building-control body and energy designer to confirm the applicable Approved Document L route, calculation area, system output, infrastructure constraints, controls, and commissioning evidence.
This guide explains the future requirement and its decision points. It does not classify a particular ADU, set a project design, or establish approval. Use the current Approved Document L, Volume 1, the official L3 FAQ, and Circular 01/2026 for the current text and transition conditions.