Approved Document L: Energy and greenhouse gas emissions, frequently asked questions
Answers to frequently asked questions on Approved Document L: Energy and greenhouse gas emissions – 2026 edition.
Applies to England
These frequently asked questions (FAQs) refer to the Approved Document L: Energy and greenhouse gas emissions (2026).
Requirement L2
How does Requirement L2 to ensure that renewable electricity generation is ‘appropriately sized for the site and available infrastructure’ interact with the new Requirement L3?
Requirement L2 requires that where an on-site electricity generation system is installed, reasonable provision is made to ensure that:
- the system and its electrical output are appropriately sized for the site and available infrastructure
- it has effective controls, and
- it is commissioned through testing and adjustment so that it produces the maximum reasonable amount of electricity under the circumstances
With the introduction of Requirement L3 any system installed to meet L3 must also comply with all other relevant Building Regulations, including L2. Reasonable provision should be made to ensure that the on‑site electricity generation system, and its electrical output, are appropriately sized for the site and infrastructure and meets the other requirements of L2.
Having considered the relevant factors, it is possible that the output of a system appropriately sized for the site and available infrastructure may differ from the output of a system calculated in accordance with paragraphs 5.73 and 5.74 of Approved Document L1 (2026 edition). Whether reasonable provision has been made will depend on the facts of the particular case.
What factors could be considered when determining if an onsite renewable electricity generation system and its electrical output are ‘appropriately’ sized for the site and available infrastructure?
Determining whether an onsite renewable electricity generation system installed to meet L3 and its electrical output, are ‘appropriately’ sized for the site and available infrastructure for the purposes of L2 will require careful consideration of any relevant site-specific factors. Relevant factors are likely to include:
- the on-site energy demand
- the capacity and nature of the available infrastructure, including export limits set by the District Network Operator
- the relationship between export limits, the level of generation and on-site energy demand
- other characteristics of the site which may affect the appropriate size of the system and/or its electrical output
The relevance and weight to be given to any particular factor will depend on the circumstances of the case.
Requirement L3 – Renewable Electricity Generation Functional Requirement
How should I use equation 5.1 of ADL1?
The process for calculating the annual output (in kWh) of a dwelling is described under “M1 Photovoltaics” in Appendix M1 of SAP 10.3.
For the purposes of meeting Requirement L3, an onsite renewable electricity generation system installed on or within the curtilage of a new dwelling-house should be designed to achieve an annual output (kWh), as calculated using the approved methodology, at least equal to that of a photovoltaic array with the specific characteristics outlined in paragraph 5.73(a). This includes installed peak power (kWp) equal to photovoltaic panels with an efficiency of 0.22kWp per m2 installed over an area equivalent to 40% of the dwelling-house’s ground floor area.
The appropriate level of installed peak power calculated using Equation 5.1, should then be used following the process in Appendix M1 of SAP 10.3 to determine the required annual output that the onsite renewable electricity generation system should be designed to achieve for the purpose of paragraph 5.73(a) of Approved Document L1.
For buildings containing one or more dwellings, AGRND (from equation 5.2) or AGRNDWELL (from equation 5.3) should be used, as appropriate, for the ground floor area described in Equation 5.1, to determine the appropriate level of installed peak power. The process in Appendix M1 of SAP 10.3, should then be used to determine the required annual output.
How do I calculate the efficiency of a solar PV panel?
For the purposes of Requirement L3, the efficiency of a panel should be calculated by dividing the output (kWp) of the panel by the area of the whole of the panel (including the frame but excluding flashings).
For the purposes of paragraphs 5.73(b) and 5.74(c), do I need to consider all roof surfaces in the calculation of the output of a photovoltaic array covering the ‘reasonably practicable roof area’ including those facing North?
Yes. Having considered the relevant design constraints, developers are responsible for identifying what constitutes the ‘reasonably practicable roof area’ on a new dwelling/building containing dwellings and justifying that assessment to the relevant building control body.
However, the lower generation resulting from an array being located on a north facing roof relative to other orientations is unlikely to be sufficient justification to exclude it from the ‘reasonably practicable roof area.’ This is because the calculation of the output of a solar array following the approved methodology accounts for impacts on generation arising from the orientation of the panels.
For the purposes of paragraphs 5.73(b) and 5.74(c), do I need to consider a roof surface that is heavily overshaded in the calculation of the output of a photovoltaic array covering the ‘reasonably practicable roof area’?
Yes. Having considered the relevant design constraints, developers are responsible for identifying what constitutes the ‘reasonably practicable roof area’ on a new dwelling/building containing dwellings and justifying that assessment to the relevant building control body.
However, the lower generation resulting from an array being overshaded is unlikely to be sufficient justification to exclude it from the ‘reasonably practicable roof area.’ This is because the calculation of the output of a solar array following the approved methodology accounts for impacts on generation arising from overshading of panels.
What defines the “curtilage of the building” in the context of Requirement L3?
For the purposes of Requirement L3, “curtilage” should be understood as land so closely and directly associated with a building as to form “part and parcel” of it. The curtilage of a building will typically include land directly adjoining and serving the building such as gardens, garages or driveways (in the case of individual dwellings) and may also include service areas, courtyards or other space used for servicing or supporting the building (including in the case of buildings containing dwellings).
Determining what falls within the curtilage should be assessed on a case-by-case basis, taking account of the relationship between the building and the land being considered and having regard to physical layout, ownership and their use or function.
What does it mean for electricity generated from a photovoltaic array to be available for the use of residents in buildings containing dwellings (e.g. blocks of flats)?
5.75 of Approved Document L1 sets out that the system for renewable electricity generation should be designed so that generated electricity is available to residents of the dwellings. In buildings containing dwellings, this could be to individual dwellings and communal spaces where the electricity can be used for the benefit of the residents of the dwellings.
Should the ground floor area (GFA) of a detached garage be included when calculating the output of a photovoltaic array covering an area equivalent to 40% of the GFA of a dwelling?
No. Unheated spaces that sit outside of the projected main roof area should not be included for the purposes of calculating the required output of a solar array covering an area equivalent to 40% of the dwelling’s GFA. This aligns with the approach taken to attached garages in relation to the notional building, as outlined in the SAP 10 conventions.
Should the roof area of a detached garage be included when calculating the output of a photovoltaic array that covers the ‘reasonably practicable roof area’?
No. The ‘reasonably practicable roof area’ refers to the roof of the dwelling or building containing one or more dwellings. The roof area of a detached garage should not be included when calculating the required output of a photovoltaic array that covers the ‘reasonably practicable roof area’ of a dwelling or a building containing one or more dwellings under 5.73(b) and 5.74(c) of ADL1.
Can I choose to install photovoltaic panels on the roof space of a detached garage to meet the required output of Requirement L3?
Yes, subject to any other relevant requirements, provided that the detached garage is within the boundaries of the curtilage of the building and the conditions in Requirement L3 are met.
How should I use the offset distances outlined in Appendix B of Approved Document L1?
Appendix B of Approved Document L1 provides practical guidance to support the safe installation, use and maintenance of photovoltaic arrays covering the “reasonably practicable roof area”, for the purpose of Requirement L3.
The Appendix B offset distances are primarily intended for determining the size of the “reasonably practicable roof area.” They are not intended to cover all circumstances and, in some cases, different offsets for installation may be appropriate, provided that the panels cover the reasonably practicable roof area to maximise generation, comply with applicable regulatory requirements and are installed according to the manufacturer’s instructions.
What part of the panel should I measure to when using the roof offset distances in Appendix B of Approved Document L1?
Roof offset measurements should be taken from the roof feature to the edge of the relevant panel.
What dimension of PV panel should I use when determining the size of a PV array that covers the ‘reasonably practicable roof area’?
There are not specified panel dimensions to be used when determining the size of a PV array that can cover the ‘reasonably practicable roof area.’ This flexibility is intended to ensure that the target output is an accurate reflection of the level of output feasible on the available roof space.
Housebuilders should use panels with dimensions that are appropriate for the context of the building’s design when determining the size of an array that covers the ‘reasonably practicable roof area.’ In most cases, it is likely that developers will use panel dimensions consistent with commercially available residential solar PV panels.