Glossary
Daylight and sunlight reports in dense London streets
A BRE-method assessment of how an extension affects neighbours' light. Required when impact is likely.
A BRE-method assessment of how an extension affects neighbours' light. Required when impact is likely.
A daylight and sunlight report models how a proposal affects light to neighbouring windows and amenity spaces, using the BRE BR 209 methodology. It is required where a scheme is tall, close to habitable windows, or has attracted a light-based objection, and it is prepared by a specialist consultant from a 3D model.
The BRE numbers: 27% vertical sky component at a neighbour’s window, or no less than 0.8 times its former value, and 25% of annual probable sunlight hours with 5% falling in winter. They are planning guidance, not law, and they are separate from a right of light easement.
| Test | Threshold | Applies to |
|---|---|---|
| Vertical sky component | 27%, or ≥ 0.8 × former value | Existing neighbouring windows |
| No-sky line / daylight distribution | area losing sky ≥ 0.8 × former | Existing rooms |
| Annual probable sunlight hours | ≥ 25% annual, ≥ 5% winter | Windows within 90° of due south |
| Overshadowing of gardens | ≥ 50% receiving 2 hours of sun on 21 March | Amenity space |
| Right of light easement | 20 years’ uninterrupted enjoyment | Private law, not planning |
| Light obstruction notice | interrupts the 20-year clock | Rights of Light Act 1959 |
Sources: BRE BR 209, Site Layout Planning for Daylight and Sunlight: a guide to good practice, 3rd edition (2022); Prescription Act 1832; Rights of Light Act 1959. Read at 1 September 2026. BR 209 is explicitly advisory — it says its numerical guidelines should be interpreted flexibly — so a scheme that misses a threshold is not automatically refused, and one that meets every threshold can still infringe a private easement.
A 3D model of the existing and proposed situation, vertical sky component results for every affected window, no-sky line plots for affected rooms, annual probable sunlight hours for windows within 90 degrees of south, and where gardens are affected, a two-hour sun-on-ground test on 21 March.
Results are presented window by window against the BR 209 targets: 27% VSC or 0.8 times the former value, no more than 20% loss of the sky-visible working plane, and 25% annual with 5% winter sunlight hours.
Before submission, if the scheme is two storeys or more and sits close to a neighbour's habitable window — it is far cheaper to adjust a massing at design stage than to defend it at appeal. After an objection, because an officer with a light objection and no evidence will usually refuse.
For a single-storey rear extension within permitted development depths, a report is almost never needed; the borough's 45-degree rule does the work.
Considerable, but not absolute. BR 209 itself warns against rigid numerical application in dense urban areas, and inspectors regularly accept shortfalls where the existing context already suppresses light. A report that explains the context, rather than only reporting numbers, is the more persuasive document.
A worked Richmond upon Thames example of daylight and sunlight report: with 72 conservation areas — the Richmond Green Conservation Area and the Kew Green Conservation Area among the best known — London Borough of Richmond upon Thames (Richmond Council) sees daylight and sunlight report constantly, and there is no borough-wide Article 4 direction, so permitted development generally survives outside conservation areas. Where daylight and sunlight report pushes a Richmond upon Thames scheme out of permitted development, the route becomes a £548 application decided in 8 weeks rather than a £249 prior approval in 6 weeks.
| Methodology | BRE BR 209 |
|---|---|
| Key metric | Vertical sky component, 27% target |
| Room test | No-sky line, 20% maximum loss |
| Sunlight test | APSH 25% annual / 5% winter |
| Garden test | 2 hours of sun on 21 March over 50% of area |
| Typical trigger | Two-storey+ near habitable windows, or an objection |
Rarely. The borough's 45-degree rule normally settles single-storey cases.
A daylight and sunlight consultant with rights-of-light modelling software.
No, but a light-based objection with no evidence against it usually means refusal.
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