Daylight and sunlight report in London

How the test works, in two stages

London guidance sets out a sequence. The Mayor's Housing Design Standards guidance says impacts are assessed by a two-stage approach: first apply the BRE guidance, then consider the location and wider context. The same document asks that at least one habitable room in a new home receives direct sunlight. That order is how an officer reads your report, so it is how we write it.

Stage one is arithmetic. Each affected window is compared before and after on the standard measures: how much open sky it sees, how far the daylight reaches into the room, and for south-facing living rooms how many hours of sun it keeps across the year. Stage two is argument. Where a window loses more than the guide treats as noticeable, the report explains the context: a corner site, an existing blank flank, a window that borrows light from a side glazed panel.

The result is a table of figures and a short, honest reading of it. We do not tune the model to hide a loss, because a report that finds none looks unconvincing to the person assessing it.

Where the numbers come from

The reference document is BR 209 'Site layout planning for daylight and sunlight: a guide to good practice', 3rd edition, published June 2022; revised to reflect BS EN 17037:2018; neighbour-impact methodology same as earlier editions; advisory only.

The guide is advisory and says so. London policy adds to that. The London Plan's housing quality policy asks for sufficient daylight and sunlight for new and surrounding housing that is appropriate for its context, and the Mayor's Housing SPG tells boroughs to apply an appropriate degree of flexibility, especially for denser sites in town centres, opportunity areas and large sites.

National policy points the same way. The NPPF expects acceptable living standards for residents and neighbours in terms of access to daylight and sunlight, and names an unacceptable loss of light for neighbouring residents as a reason a proposal can fall short. None of this sets a pass mark. It sets a judgement, and the report is the evidence for it.

The simple screen before any report

Borough design guides often use a geometric screen first. A common one is the 45-degree test: a line drawn at that angle from the centre of the nearest affected window, in plan and in elevation, should not be crossed by the new extension. Each council words its own version, so we read yours.

The test is worth running before the design is fixed. A few centimetres of eaves height or one structural bay of depth can move a line from clear to crossed, and changing a drawing at that stage costs nothing. Our planning drawings are built in a three-dimensional model, so the line can be checked against every opening on the neighbouring elevation in minutes.

If the line is cleared, the case is usually straightforward. If it is crossed, a full report with the BRE measures is how you show the effect is small, or acceptable for the street.

When a council will ask for a report

There is no blanket national requirement. The validation rule is precise: A daylight/sunlight report is a validation requirement only if it is on the council's local list (published less than 2 years before submission). A list older than that cannot be used to reject an application as invalid.

Outside the local list an officer can still ask for one during the case, usually after a neighbour objects about light. That is slower and more stressful than supplying it up front, which is why we read the local list and recent decisions in the free check and tell you which of three answers applies: required, sensible precaution, or not worth the money.

What you receive and what it costs

The report contains the model, a schedule of the neighbouring windows tested and the rooms behind them, results before and after, a plain-English conclusion, and where useful the design change that would improve a result. Overshadowing of neighbouring gardens is tested separately. A second MCIAT chartered architectural technologist, who did not build the model, checks the geometry and the figures before issue.

There is no list price, because the cost follows the number of windows and the site. You get a fixed quote after a free constraints check, and the council's own application fee is paid to the council separately.

Basements raise separate ground and water questions, covered under basement impact assessment. If the wider argument for permission is the hard part, our planning consultant service handles that. To see how a borough you know treats the issue, start with daylight and sunlight reports in Camden or in Wandsworth.