A daylight report is a technical assessment that measures how much natural light reaches a building or window — and whether a proposed development will reduce that light to an unacceptable level. In the UK, local planning authorities regularly require one before granting consent for new residential blocks, extensions, office conversions, and any scheme likely to affect neighbouring properties. Get it wrong and your application can stall; get it right and it becomes one of the strongest tools in your planning strategy.
This guide explains what a daylight report actually contains, the standards it must meet, and the specific situations where you will almost certainly need one submitted with your planning application.
What a Daylight Report Measures
A daylight report assesses natural light using two primary metrics set out in BRE BR 209: Site Layout Planning for Daylight and Sunlight (2022 edition):
- Vertical Sky Component (VSC) — the proportion of sky visible from the centre of a window. BRE's target is 27% or above. If a window falls below 27% VSC, the new value should retain at least 0.8x (80%) of its former level to be considered acceptable.
- No-Sky Line (NSL) — the line within a room beyond which no direct skylight reaches the working plane. BRE recommends that at least 80% of a room's floor area should receive direct skylight.
For sunlight, the main measure is Annual Probable Sunlight Hours (APSH). BRE targets 25% of annual probable sunlight hours overall, with at least 5% in winter (October to March). A window failing both the annual and winter tests is considered to experience a noticeable impact.
Since the 2022 revision of BR 209, daylight to new dwellings is now assessed under BS EN 17037: Daylight in Buildings rather than the old Average Daylight Factor (ADF). This matters: if your scheme includes new residential units, the target-setting framework has changed, and older reports prepared under the 2011 edition may no longer satisfy your local authority.
When Does UK Planning Require a Daylight Report?
There is no single national threshold that triggers a daylight assessment automatically. Instead, the requirement is driven by local planning policy, pre-application advice, and the nature of the scheme. In practice, you should commission a daylight report in the following situations:
- New residential development — any block of flats, apartment conversion, or housing scheme where the massing is likely to reduce daylight or sunlight to nearby properties.
- Extensions that cross the 45-degree rule — if your extension breaks the 45-degree angle drawn from the centre of a neighbouring window (in plan or elevation), most councils expect a BRE assessment to accompany the application.
- Office-to-residential conversions — permitted development or full application, the introduction of habitable rooms in a formerly non-residential envelope often prompts a BS EN 17037 internal assessment.
- Schemes in sensitive locations — conservation areas, tight urban sites, or boroughs with specific daylight policies (notably in London) require earlier and more detailed assessment.
- Applications where a neighbour objects on daylight grounds — even for a relatively modest scheme, a planning officer may condition a report to resolve a third-party objection.
If you are unsure whether your scheme needs one, the safest step is to ask at pre-application stage. Most councils provide paid pre-app advice, and the answer will be in writing — useful if the requirement is later disputed.
What the Report Must Cover
A compliant UK daylight report under BR 209 (2022) typically contains:
- A site description and description of the proposed development
- Identification of all neighbouring windows and rooms that could be affected
- VSC analysis for each affected window in its existing and proposed-development state
- NSL analysis for each affected room
- APSH analysis for windows that receive direct sunlight
- An overshadowing study for neighbouring gardens and amenity spaces (BRE recommends 50% of the area should receive two hours of sunlight on 21 March)
- A conclusions section comparing results against BRE targets and explaining any shortfalls
Where shortfalls occur, a good report does not simply flag them — it sets out whether the impact is noticeable or harmful under the BRE's own language, and where possible proposes design amendments or justification for why the impact is acceptable in context. See our daylight and sunlight services page for details on what Fortress Associates includes as standard.
Daylight Reports and the London Plan
If your scheme is in Greater London, the London Plan 2021 adds another layer. Policy D6 (Optimising housing density) and the accompanying GLA guidance reference daylight and sunlight directly, and boroughs such as Westminster, Camden, and Hackney each have supplementary planning documents that go beyond the BRE targets. In practice, this means a London scheme may need the report earlier — sometimes before the design is fixed — to avoid costly revisions at validation stage.
Our building regulations and daylight services cover the full range of London borough requirements. If you are working in a specific borough, the contact page is the fastest way to confirm the local policy position before you commit to a design.
How Long Does a Daylight Report Take?
At Fortress Associates, a standard daylight and sunlight report takes 4–5 working days from receipt of drawings. No advance payment is required — you pay on completion once you have seen the draft. For straightforward residential extensions, the report can often be delivered faster; for large mixed-use schemes with many affected neighbours, allow more time for the 3D modelling and window schedule preparation.
Turnaround is one of the most common questions we receive. Planning validation teams typically require the report to be submitted with the application — not as a post-submission document — so commissioning it early avoids delays at the start of the statutory determination period.
How Fortress Associates Can Help
Fortress Associates prepares daylight and sunlight reports to BRE BR 209 (2022) and BS EN 17037 for residential, commercial, and mixed-use schemes across the UK. Reports are delivered in 4–5 working days with no advance payment. Whether you need a straightforward neighbour-impact assessment for a rear extension or a detailed internal daylight study for a new residential scheme, our daylight report service is designed to give your planning application the technical backing it needs. Get in touch today for a no-obligation quote.
Sources & Further Reading
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