Daylight and Sunlight Assessments in Merton

Merton asks for daylight and sunlight evidence more readily than most outer London boroughs, and it uses a particular phrase: "daylight, sunlight and overshadowing assessment". We see it in pre-application responses for new houses on garage and backland plots in Wimbledon, Merton Park and Raynes Park, in validation letters for flats above the parades on Coombe Lane and Kingston Road, and in officer requests on workshop sites behind the terraces of Colliers Wood and Mitcham. The word "overshadowing" is doing work: the council wants to see a shadow study of neighbouring gardens as well as the window tests.

Our Merton reports are titled and structured to match that request, so the officer can see at a glance that each part of the council's wording has been answered. Where the scheme also creates new homes, we assess daylight inside them against the BRE targets, which is where most of the design work in Merton tends to happen. Reports usually take 4–5 working days.

Recent daylight and sunlight assessments in Merton

Chester Road, Wimbledon – new house on a former garage site

A new house on a former garage site off Chester Road, close to Wimbledon Common. Merton's pre-application response asked for a daylight, sunlight and overshadowing assessment, although the nearest houses on West Side Common and Chester Road, and the edge of Cannizaro Park, are around 30 metres or more away. All tested windows and gardens met the BRE daylight and sunlight guidelines, and a 21 March shadow study showed no material overshadowing of neighbouring gardens. The report was titled to match the council's wording and issued in December 2025 ahead of the full planning submission.

Walpole Road, Colliers Wood – roof extension and two new houses on a workshop site

An extended replacement roof creating a new flat, and two three-bedroom houses replacing rear workshops, close to neighbouring gardens and windows. The developer wanted to know early whether there was room to enlarge the footprint. Every neighbouring window and garden met the BRE daylight and sunlight guidelines with margin to spare, so we shared the results first and the assessment became a design tool. A small ground floor extension and a moved window were re-tested, and the final report was issued in March 2026 for the planning application.

Coombe Lane, Raynes Park – new flats above a shopping parade

New flats above a parade of shops on Coombe Lane, needing an internal daylight and sunlight assessment and a neighbour impact report. Early layouts left several upper-floor rooms well short of the BRE daylight target and a handful of neighbouring windows short of the VSC and sunlight guidelines. Across several revisions, stepped-back upper floors, rooflights, larger glazing and re-planned internal walls brought almost all of the rooms within the target, with the remaining small shortfalls and one marginal neighbouring window explained in the reports. Separate internal reports and the neighbour report were issued in March 2025.

What Merton planning officers look for

Merton determines applications against the Merton Local Plan 2024, adopted on 20 November 2024 and running to 2037/38, read with the London Plan. Policy D12.3 requires development to demonstrate that acceptable levels of light will be available to its surroundings, and the plan says when evidence is expected: a daylight and sunlight assessment is required for all major development, for the creation of new dwellings, and for any development with the potential to affect the daylight and sunlight currently enjoyed by existing properties. Assessments are expected to include overshadowing studies with shadow diagrams at hourly intervals at different times of year, and where a scheme includes single-aspect units the plan looks for internal daylight evidence using VSC and Average Daylight Factor.

For householder and small schemes, the council's Extensions and Alterations to Dwellings guidance and, for infill and backland plots, the Small Sites Toolkit SPD set out the design criteria officers use to judge the effect on a neighbour's light and outlook. The numerical assessment follows BRE BR 209, Site layout planning for daylight and sunlight (2022 edition). The Local Plan is at merton.gov.uk/planning-and-buildings/planning/local-plan and the supplementary documents at merton.gov.uk/planning-and-buildings/planning/supplementary-planning-documents.

When you need an assessment in Merton

• A new house on a garage or garden plot in Wimbledon, Merton Park or Wimbledon Park, where the Local Plan requires an assessment for any new dwelling and the pre-application response will say "daylight, sunlight and overshadowing".
• Backland houses behind the terraces of Colliers Wood, South Wimbledon and Mitcham, where the new buildings sit close to several rear gardens.
• Flats above the parades on Coombe Lane, Kingston Road and London Road, Mitcham, where single-aspect rooms need internal daylight evidence as well as the neighbour tests.
• Deep or two storey rear extensions on the Edwardian streets of Raynes Park and Wimbledon Chase, where a neighbour has raised concerns about loss of light.
• Small sites and infill plots in Morden and Lower Morden assessed under the Small Sites Toolkit SPD.
• Any scheme where Merton's pre-application advice or validation checklist has listed a daylight and sunlight assessment.

How we work

We model the site and its neighbours from the drawings, survey data and photographs, or from your own SketchUp model, run the BRE tests and the shadow study, and send a report whose title and sections match what the council has asked for. The fee is fixed and agreed up front and the report usually takes 4–5 working days. Where a room or window falls short we say how far and what change would remove the shortfall, and we will re-test revised drawings within the same job. The four tests are:

• Vertical Sky Component (VSC) – the sky a neighbouring window can see, before and after.
• No-Sky Line / daylight distribution (NSL) – how far daylight reaches into the neighbour's room.
• Annual Probable Sunlight Hours (APSH) – direct sun to windows within 90 degrees of south, annually and in winter.
• Sun on ground – the share of a garden that gets two hours of sun on 21 March, with hourly shadow diagrams where Merton asks for them.

See our VSC, NSL and APSH page and our guide to the BRE guidelines for the tests, and our daylight and sunlight assessment page for the service.

Frequently asked questions in Merton

Merton has asked for a "daylight, sunlight and overshadowing assessment" but my neighbours are 30 metres away. Do I still need one?

If the council has asked, it is worth answering properly; a short report that shows the separation distances and a 21 March shadow study will usually settle the point quickly, as it did at Chester Road.

Can you tell me the results before writing the report, so I can change the design?

Yes. In Merton we often do, particularly on backland sites where there may be room to go bigger. At Walpole Road the developer saw the raw results first and adjusted the scheme before the report was written.

What happens if the flats above my parade do not meet the daylight target?

We tell you which rooms are short and by how much, and suggest the changes that work: larger or taller windows, rooflights over bedrooms, or moving utility space into the darkest corners. Then we re-test the revised layout, as many times as it takes, before the final reports are issued.

North of the borough, our Wandsworth page covers the same work across Southfields and Earlsfield.

Get a fixed-fee quote

Send the drawings, the address and the council's letter through our contact page, or use the price calculator for an instant figure. Nick is on 01962 809155 and nick@sunlightassessments.co.uk.