Daylight and Sunlight Assessments in Westminster

If you are planning a new development or extension in the City of Westminster, a daylight and sunlight assessment is often a key requirement for securing planning permission. Whether you are extending a period property in Marylebone or Belgravia, adding a rear or roof extension in Pimlico or Bayswater, or proposing a new residential development in Paddington, Maida Vale or St John's Wood, your proposals may affect the daylight and sunlight enjoyed by neighbouring properties and Westminster's planning officers will expect you to demonstrate that any impacts are acceptable.

At Sunlight Assessments, we prepare BRE-compliant daylight and sunlight assessments for planning applications across the City of Westminster. Our reports are clear, technically robust, and written to support a smooth planning process.

When does Westminster require a daylight and sunlight assessment?

Not every application in Westminster will require a formal assessment, but there are common scenarios where one is expected:

• Extensions that extend close to a boundary with a neighbouring property, particularly where habitable rooms face the affected elevation
• New residential developments where neighbouring properties may lose access to natural light
• Applications where the Local Planning Authority has identified daylight and sunlight as a material planning consideration
• Rear, mansard and roof extensions in tightly built terraces and mansion blocks, where neighbouring windows may be particularly close to the proposed works
• Conversions and changes of use where new habitable rooms are proposed

If you are unsure whether your scheme requires an assessment, we are happy to advise on this at no cost.

Westminster's local planning policy

Westminster's approach to daylight and sunlight is guided by its City Plan 2019-2040, adopted in April 2021, with a partial review adopted in January 2026. The City Plan sets out the council's vision and policies for development across the city and forms the basis on which planning applications are determined. Its design and amenity policies require development to be provided with sufficient levels of daylight and sunlight appropriate to their context, and to protect the amenity of neighbouring occupiers. In assessing the impact of development on natural light, Westminster uses the methodology set out in the BRE guidance document BR 209: Site layout planning for daylight and sunlight (2022 edition) as its starting point - the nationally recognised benchmark for daylight and sunlight assessments in the UK. The council acknowledges that, given the dense and historic character of much of the city, it may not always be possible to meet the BRE standards in full, and results are therefore considered in their local context.

For householder applications such as extensions, roof alterations and loft conversions - Westminster's collection of supplementary planning documents and householder guidance provides detailed advice on how the council's policies should be applied to residential alterations and extensions. This guidance is a key reference point for schemes where the impact on neighbouring amenity, including natural light, is a consideration, and should be read alongside the adopted policy framework.

You can find Westminster's planning policies at westminster.gov.uk/planning-building-control-and-environmental-regulations/planning-policy/westminsters-planning-policies and the council's supplementary planning documents and guidance at westminster.gov.uk/planning-building-control-and-environmental-regulations/planning-policy/supplementary-planning-documents-and-guidance.

How the assessment works

We use the methodology set out in BRE BR 209 to assess the impact of proposed development on daylight and sunlight. The key tests we carry out include:

Vertical Sky Component (VSC): This measures the amount of sky visible from the centre of a window. BRE guidance recommends that a VSC of 27% or more is generally considered adequate. Where a development results in a VSC that is less than 0.8 times its former value, the reduction may be noticeable to occupants.

No-Sky Line (NSL): This assesses the distribution of daylight within a room by plotting the line beyond which no sky is visible. Where the area of a room that can receive direct skylight is reduced by more than 20%, occupants are likely to notice a deterioration in the quality of daylight.

Annual Probable Sunlight Hours (APSH): This test is used to assess access to sunlight for windows that face within 90° of due south. It considers both the winter and annual totals to determine whether sunlight losses are likely to be material.

Where appropriate, we also carry out sun-on-ground studies to assess the impact on garden or amenity spaces.

What our Westminster report includes

Our daylight and sunlight assessments for Westminster planning applications typically include:

• A clear description of the proposed development and the surrounding context
• Identification of all relevant neighbouring windows and amenity spaces
• VSC and NSL calculations for affected neighbouring properties
• APSH calculations where required
• A comparison of results against BRE BR 209 benchmarks
• A professional assessment of whether any identified impacts are likely to be considered material in planning terms
• Recommendations for design amendments where required, to help reduce impacts and support approval

All reports are produced by qualified consultants with experience of working across the City of Westminster.

Get in touch

If you are planning a development in Westminster and would like to discuss whether you need a daylight and sunlight assessment, please get in touch. We offer a free initial consultation and can usually turn around a report within 5 working days of receiving the necessary information.