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Daylight & Sunlight Assessments

Ensure planning success and create spaces that perform.

Our specialist daylight and sunlight assessments deliver precise, BRE-compliant analysis to support planning applications, guide architectural design, and improve the quality of residential and commercial environments.
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What is a Daylight Sunlight Assessment?

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.

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BRE Guidelines and Standards

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.

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Daylight & sunlight Key Assessment Components

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.

London TM59
9 unit TM59

Daylight & sunlight technical Analysis and Calculations

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.

When are daylight & sunlight assessments required?

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.

Site plan TM59
Elevations TM59

Benefits for Development Projects

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.

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Assessment Deliverables

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.

Elevations TM59
Orientation TM59

How do I book?

The typical process for a daylight sunlight assessment follows these key stages:

- Initial Consultation - Determine the scope and requirements based on the development’s location and characteristics
- Site Visit and Data Collection - Gather information about existing buildings, window positions, and site conditions
- 3D Model Creation - Develop accurate digital models of existing conditions and the proposed development
- Technical Analysis - Perform calculations for VSC, APSH, and other metrics using specialist software
- Report Production - Compile findings into comprehensive documentation for planning submission
- Design Feedback - If issues are identified, provide recommendations for design modifications
- Planning Support - Assist with responses to any questions raised during the planning process

Once you've accepted our quote, we’ll just need your invoicing details. And you'll receive the report with 5 working days.

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Importance of Early Design Stage Assessments

A 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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Frequently Asked Questions

FAQ Section

What is a Daylight and Sunlight Assessment?
Why do I need a daylight and sunlight report for my planning application?
What standards do you follow in your assessments?
Is a daylight and sunlight report the same as a Right to Light survey?
Do I need a daylight and sunlight assessment for a small extension?