A daylight sunlight assessment is a comprehensive evaluation that measures how proposed developments impact existing daylight and sunlight levels in surrounding properties.
This technical analysis is typically required by local planning authorities to support planning applications for new buildings and significant modifications to existing structures.
The assessment examines two distinct but related aspects:
- Daylight: The diffuse, ambient light from the sky in the absence of direct sunlight
- Sunlight: Direct solar rays reaching a building or open space
These assessments ensure neighbouring properties maintain adequate natural light access while enabling sustainable development. They serve as a critical tool for developers to demonstrate compliance with established guidelines and standards.
For many development schemes, particularly in urban areas, these assessments are not optional—they’re essential for navigating the planning process successfully.
The Building Research Establishment (BRE) provides the primary technical framework for daylight and sunlight assessments through its publication BRE 209 “Site Layout Planning for Daylight and Sunlight – A Guide to Good Practice.”
This document establishes the methodology and acceptable thresholds for evaluating natural light impacts.
Additionally, British Standard BS EN 17037:2018 sets minimum daylight requirements for buildings and spaces, introducing more nuanced, climate-specific considerations for different European locations.
These guidelines establish:
- Acceptable levels of daylight reduction for existing properties
- Minimum standards for new developments
- Methodology for assessing overshadowing impacts
- Criteria for evaluating impacts on gardens and amenity spaces
Local planning authorities typically reference these standards when evaluating planning applications, making compliance essential for development approval. The guidelines help balance development needs with protection of neighbouring amenity and light quality.
A thorough daylight sunlight assessment comprises several technical components, each measuring different aspects of natural light access:
- Vertical Sky Component (VSC)VSC calculations measure the diffuse daylight reaching windows before and after development.
According to BRE guidance, a VSC of 27% or more indicates good access to daylight. If a proposed development would reduce the VSC to less than 0.8 times its former value, the loss of light is considered significant and may require mitigation measures.
Annual Probable Sunlight Hours (APSH)APSH analysis evaluates the sunlight hours a window receives throughout the year, with particular attention to living rooms that have the highest sunlight needs. The BRE guidelines recommend:
- At least 25% of annual probable sunlight hours overall
- At least 5% of annual probable sunlight hours during winter months
No Sky Line
Also known as the Daylight Distribution test, this assessment determines how much of a room’s floor area receives direct skylight. If the proposed development would reduce this area to less than 0.8 times its former value, the impact is considered adverse.
Shadow Studies
These track overshadowing impacts on gardens, amenity spaces, and neighbouring buildings throughout the year. The BRE guidance suggests that at least half of any garden or amenity space should receive at least two hours of sunlight on March 21st (the spring equinox).
Site Survey and Data Collection
Every daylight and sunlight assessment begins with a detailed site survey to document existing conditions. This typically includes:
- Building orientations and window positions in surrounding properties
- Photography and measurements of neighbouring buildings’ windows
- Assessment of trees, existing obstructions, and reflective surfaces
- Documentation of outdoor spaces that might be affected
The data collected forms the foundation for 3D modeling of the site and its surroundings using specialist software. This digital model enables accurate simulation of light conditions before and after the proposed development.
The technical heart of a daylight sunlight assessment lies in its detailed calculations and computer-based modeling.
This includes:
- Evaluation of living rooms, kitchens, bedrooms, and sometimes commercial spaces in neighbouring buildings
- Assessment of potential solar panel impacts on adjacent properties
- Analysis of reflective glare from proposed development surfaces
- Comparison of existing versus proposed conditions against BRE numerical guidelines
These calculations require specialized software and expertise to interpret correctly. The results determine whether the proposed development meets acceptable standards or requires design modifications.
Local authorities typically require daylight and sunlight assessments in the following scenarios:
- Planning applications for developments that may impact neighbouring properties’ natural light access
- High-density urban developments where overshadowing risks are elevated
- Extensions or alterations to existing buildings affecting adjacent properties
- Commercial and residential developments exceeding specific height or proximity thresholds
The exact requirements vary between local planning authorities, but assessments are most commonly needed when:
- The proposed development is substantially taller than surrounding buildings
- The site is in a dense urban environment
- The development is in close proximity to residential properties
- There are sensitive receptors nearby (like schools or hospitals)Early consultation with planning authorities can help determine whether an assessment is necessary for your specific project.
Beyond regulatory compliance, a well-executed daylight sunlight assessment offers numerous strategic advantages for development projects:
- De-risks the planning process by identifying potential objections before application submission
- Influences optimal building heights, glazing ratios, and site layout design decisions
- Reduces neighbour objections and planning delays through early identification of issues
- Supports energy-efficient building designs by maximizing natural light while minimizing overshadowing
A thorough assessment can help design teams optimize the development scheme to balance maximizing the site’s potential with minimizing adverse impacts on surrounding properties.
A comprehensive daylight sunlight assessment typically includes:
- Technical Reports - Detailed documentation with visual data, calculations, and compliance analysis
- 3D Models - Visual representations of the development and its surroundings
- Shadow Studies - Seasonal and daily overshadowing patterns showing impact throughout the year
- Recommendations - Design modifications if BRE guidelines are not met
- Planning Documentation - Supporting materials formatted for submission to local authorities
These deliverables help demonstrate to planning authorities that the development has been designed with due consideration for its impact on the surrounding built environment.
The typical process for a daylight sunlight assessment follows these key stages:
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Submit an enquiryInstant QuoteA professional daylight sunlight assessment is not merely a planning requirement—it’s a valuable tool that supports better design decisions and smoother project delivery. By understanding the technical aspects and benefits of these assessments, developers can transform a regulatory requirement into a strategic advantage.
For complex projects in sensitive locations, commissioning an assessment early in the design process can identify potential issues before they become costly problems. This proactive approach helps ensure your development not only meets regulatory requirements but also contributes positively to the built environment through thoughtful consideration of natural light.
The most successful developments balance maximizing site potential with protecting the amenity of existing properties—and a thorough daylight sunlight assessment is key to achieving this balance.
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FAQ Section
A daylight and sunlight assessment evaluates how much natural light a proposed or existing building receives, as well as the impact it may have on neighbouring properties. It ensures compliance with industry standards—most commonly the BRE guidelines—and helps support planning applications.
Most local planning authorities require these reports to assess whether your development may adversely affect the light received by surrounding buildings or open spaces. They are especially important for projects in dense urban areas or where overshadowing may be a concern.
We follow the Building Research Establishment (BRE) Guidelines:Site Layout Planning for Daylight and Sunlight – A Guide to Good Practice
These are the most widely accepted industry standards used by planning officers across the UK.
No. While they are related, a daylight and sunlight assessment is for planning purposes, based on BRE guidance. A Right to Light survey is a legal matter under common law, often used in compensation claims. We can advise on both if needed.
Possibly. It depends on the size, scale, and location. Even small developments near sensitive boundaries (like party walls or garden fences) may trigger requirements from the planning authority.