Daylight and Sunlight Assessments

for UK Planning Applications

BRE-compliant reports supporting planning decisions across the built environment

PassiHVAC provides professional Daylight and Sunlight Assessments to support planning applications across the UK. Our assessments are primarily prepared in accordance with BRE Guidance BR209 – Site Layout Planning for Daylight and Sunlight, while also drawing, where appropriate, on relevant British and European standards such as BS EN 17037+A1 (2021): Daylight in Buildings.

Our work is tailored to meet local planning authority validation requirements and reflects how daylight and sunlight evidence is interpreted in real planning decisions.

We collaborate closely with developers, architects, planning consultants, and local authorities to deliver clear, robust, and planning-ready daylight and sunlight reports that withstand technical scrutiny and support efficient determination.

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Why daylight and sunlight matter in planning?

Access to daylight and sunlight is fundamental to residential amenity, housing quality, and occupant wellbeing. Within the UK planning system, they are key considerations where new development may affect:

Existing neighbouring residential properties
Proposed habitable rooms within new dwellings
Living rooms, kitchens, and other sensitive spaces

Local planning authorities routinely require quantitative daylight and sunlight evidence to demonstrate that a proposal delivers an acceptable living environment and does not result in undue harm to neighbouring amenity.

When is a daylight and sunlight assessment required?

A Daylight and Sunlight Assessment is typically required where a proposed development may affect daylight or sunlight to existing or proposed residential accommodation. This commonly includes:

New residential developments
Extensions and upward developments
Infill and backland schemes
Developments in dense urban or constrained locations

Requirements are usually set out within local validation lists and assessed primarily against BRE BR209 guidance, with professional judgement applied to reflect site context and baseline conditions.

Daylight and sunlight in UK planning policy and standards

In the UK planning system, daylight and sunlight are not assessed in isolation. They form part of wider considerations relating to residential amenity, housing quality, and sustainable development.

While BRE BR209 remains the principal reference document for planning purposes, BS EN 17037: Daylight in Buildings provides a complementary framework focused on internal daylight provision, visual comfort, and occupant wellbeing.

Importantly:

BRE BR209 is typically relied upon for assessing impacts on neighbouring properties
BS EN 17037 may be used to inform the assessment of daylight provision within new residential units, where appropriate

BRE guidance is advisory rather than prescriptive, and professional judgement is essential when interpreting results—particularly in established urban environments.

Our approach

All assessments are undertaken using industry-recognised 3D modelling and daylight simulation software. Existing and proposed conditions are modelled accurately to ensure results are transparent, repeatable, and technically defensible.

Our methodology includes:

Accurate 3D representation of site context and surrounding buildings
Baseline and proposed condition modelling
Application of appropriate daylight and sunlight metrics
Clear documentation of assumptions and limitations

Quantitative outputs are supported by planning-led interpretation, ensuring findings are meaningful to planning officers and decision-makers.

Some important daylight and sunlight metrics

Vertical Sky Component
(VSC)

Measures the amount of visible sky at a window and is commonly used to assess impacts on existing neighbouring properties.

Annual Probable Sunlight Hours (APSH)

Evaluates the availability of direct sunlight at windows over the course of the year and is used where sunlight access is a material planning consideration.

Average Daylight Factor
(ADF)

ADF is the ratio of internal daylight to external illuminance under overcast sky conditions. The ADF metric is selectively used for daylight assessment and the results are interpreted with caution.

Spatial Daylight Autonomy
(sDA)

In new residential developments, the sDA is often used as a metric to demonstrate adequate daylighting is received during the occupied hours across the entire room.

Designed for Planning Officer Review

Our reports are structured to align with how planning officers assess daylight and sunlight impacts in practice, including:

Clear executive summaries
Transparent modelling methodology and assumptions
Window-by-window and room-by-room results tables
Annotated figures and visual outputs
Conclusions written directly against BRE guidance, standards, and planning policy

This clarity reduces ambiguity, limits requests for clarification, and supports efficient determination.

Professional Judgement in Urban Contexts

Many developments are located within dense urban environments where BRE target values may not always be achievable. In such cases, we provide:

Context-led interpretation of results
Assessment of relative change, not absolute values alone
Consideration of existing baseline conditions
Planning-focused justification supported by precedent
Mitigation and design optimisation advice where appropriate

This balanced approach ensures decision-makers are presented with credible, proportionate, and policy-aligned evidence.

Frequently asked questions

Is BS EN 17037 used for planning assessments in the UK?

BS EN 17037 is not a direct replacement for BRE BR209 in planning. It is primarily used to assess internal daylight quality within new buildings, while BRE BR209 remains the principal reference for assessing impacts on neighbouring properties.

Is Average Daylight Factor still recommended?

ADF is no longer recommended by BRE for assessing impacts on neighbouring properties. While it may still be used in limited circumstances for internal assessment of new dwellings, modern practice favours spatial or illuminance-based metrics that better reflect occupant experience.

What is the No Sky Line (NSL) and why is it important?

The No Sky Line identifies the boundary within a room beyond which skylight is no longer visible. It provides insight into daylight distribution within a space, rather than just daylight availability at the window, making it a valuable complementary metric. We also generate NSL diagrams if required for planning and compliance.

How is daylight assessed in new residential developments?

New residential units may be assessed using a combination of metrics, including VSC, illuminance-based assessments, and, where appropriate, ADF. The approach is selected based on site context and local authority expectations.

What happens if BRE targets are not met?

BRE guidance is advisory. Where targets are not achieved, developments may still be acceptable if impacts are justified through contextual analysis, professional judgement, and planning precedent - particularly in urban environments.

When should I conduct a daylight assessment or engage an expert?

Ideally, the sooner the better. If we can assess your design proposal even when it is in the schematic phase, it will save you time and resources later to make changes to comply with daylight in planning. If the daylight assessment indicates poor performance or limits sunlight in the neighbouring property, then making interventions will be difficult, and convincing the planning authority of the merit of your proposal will be even more challenging.

Ready to discuss your next project?

Every building is different, and so is every client. At PassiHVAC, we place genuine value on long-term professional relationships, not one-off compliance transactions. Many of our clients return to us because we take the time to listen, understand their priorities, and provide advice that supports their wider objectives, not just the immediate regulatory requirement.

If you are in your early phase of design or have already finalised n your design, we are happy to assist you in determining the best possible option for ensuring daylight compliance. Before any formal appointment, we are happy to have an initial, no-obligation discussion to understand your design, project, and planning requirements. We will explain the most appropriate assessment methodology and metric for ensuring compliance. Our aim is to make the assessment robust and convey the merit of your design to the planning authority for achieving compliance.

Contact PassiHVAC today to start a conversation. We look forward to working with you, supporting your current project, and building a trusted professional relationship.

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