Daylight and Sunlight Assessments in Hounslow

Daylight and sunlight are common issues in Hounslow planning applications, and showing that your scheme respects a neighbour's light is often key to securing planning permission. Whether you are extending a period home in Chiswick or Brentford, altering a property in Isleworth or Feltham, or promoting a larger residential development around Hounslow town centre, Osterley or Heston, the effect of your proposals on surrounding homes is likely to be scrutinised and it falls on the applicant to show that any loss of light is acceptable.

At Sunlight Assessments, we prepare BRE-compliant daylight and sunlight assessments for planning applications across the London Borough of Hounslow. Our reports are clear, technically robust, and written around the specific policy tests Hounslow uses to determine applications.

When is an assessment needed in Hounslow?

Not every application requires a formal study, but one is commonly expected where:

• 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
• Side and rear extensions or loft conversions in tightly built Victorian and Edwardian terraces, 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.

Hounslow's planning policy in detail

Hounslow determines applications against its adopted Hounslow Local Plan (adopted September 2015), read together with the Mayor's London Plan. A new Local Plan covering the period to 2041 has been progressing through the plan-making process, but the 2015 plan remains the adopted basis for decisions. Its design and amenity policies require new development to protect the living conditions of neighbouring occupiers, including their access to daylight, sunlight, outlook and privacy.

What is particularly useful about Hounslow's approach is that its guidance translates the principle of protecting light into concrete limits for householder work. To help prevent unacceptable loss of daylight and sunlight to neighbours, the council sets maximum depths for rear extensions according to house type - generally 3.05m for terraced houses, 3.65m for semi-detached houses and 4.25m for detached houses. Proposals that stay within these figures are less likely to raise a light objection; those that go beyond them will usually need to justify the impact, often through a daylight and sunlight assessment.

This householder guidance now sits within Hounslow's Character, Sustainability and Design Codes SPD, adopted in May 2024, which superseded the earlier Residential Extension Guidelines SPD and brings the borough's design codes, including its expectations on amenity, extension depth and overshadowing, into a single document. The SPD is read alongside the Local Plan and is a practical reference point for anyone extending or developing a home in the borough.

For the numerical assessment, Hounslow relies on the Building Research Establishment's guidance, BR 209: Site layout planning for daylight and sunlight (2022 edition), the nationally recognised benchmark. In practice, a Hounslow scheme is often considered both against the council's dimensional extension limits and, where warranted, the BRE metrics of VSC, NSL and APSH.

You can review Hounslow's adopted Local Plan at hounslow.gov.uk/local-plan, the Character, Sustainability and Design Codes SPD at hounslow.gov.uk/planning-policy/character-sustainability-design-codes-spd, and the borough's wider supplementary planning documents at hounslow.gov.uk/planning-policy/supplementary-planning-documents-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 Hounslow report includes

Our daylight and sunlight assessments for Hounslow 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 London Borough of Hounslow.

Get in touch

If you are planning a development in Hounslow 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 turn around a report within 5 working days of receiving the necessary information.