3D Design Bureau

If you are preparing a planning application or reviewing the design of a proposed scheme, daylight and sunlight requirements can raise a number of practical questions. In this guide, our team answers ten of the questions most frequently raised by clients and design teams, covering the guidance to follow, the scope of an assessment, how results should be interpreted and the design considerations that can help improve performance.

The following are the top questions we at 3DDB get asked all the time. Further detailed information is available through other articles in the links below.

Which guidelines should be used?

It is the opinion of 3D Design Bureau that the best practice for daylight and sunlight assessments is to follow the guidance of the BRE Guidelines (BRE 209). Internal daylighting to units should also be tested under IS-EN 17037 standards, and compliance rates given for both. For a detailed look at the guidelines and standards to use for daylight and sunlight assessments, visit “Expert insights on the BRE daylight and sunlight assessment guidelines“.

Do you need to test the entire scheme for internal daylighting?

Whilst it does state in the BRE 209 that daylight access will improve the higher up a building you go (due to less external obstruction), the best practice is to test the entire scheme. This means all habitable rooms of all units. This provides a clear understanding of the performance of a building. It is also a requirement under the DCC Development Plan. For more detailed information on this metric and others, visit “All you need to know about scheme performance” and “All you need to know about impact assessments”.

Do you need to include trees in daylight and sunlight assessments?

Yes, absolutely. Trees that could materially influence daylight or sunlight conditions should be represented within the analytical model. This can include existing trees to be retained, trees proposed for removal and new planting included as part of the landscape design.

Their treatment will depend on the type of assessment being undertaken, the seasonal conditions relevant to the metric and the available information. For full details on how to include trees in daylight and sunlight assessments, visit “A professional take on trees for daylight and sunlight assessments“.

What is the target compliance rate for scheme performance?

There is no single overall compliance percentage within BRE 209 that determines whether an entire proposed development passes or fails.

Individual rooms, windows and external amenity spaces are assessed against the recommendations relevant to each metric. The resulting compliance rates should then be reported to provide a clear overview of the scheme’s performance, but that overall percentage should not be interpreted as a universal planning threshold.

A proposed development should seek to achieve the strongest results reasonably possible. Different projects will achieve different compliance rates due to numerous circumstances of the scheme such as design and site constraints. Urban schemes, for example, will in most cases perform lower than the same scheme in a more expansive suburban environment.

Is there a target compliance rate for sunlight exposure (SE)?

There is no single overall scheme performance compliance rate prescribed specifically for sunlight exposure (SE). The assessment considers whether relevant dwellings achieve the applicable sunlight recommendations, while the resulting compliance rate provides a transparent overview of performance across the proposed development.

As with the other scheme performance metrics, the overall percentage should be interpreted alongside the location and orientation of the affected dwellings, the extent of any shortfall and the particular constraints of the proposed scheme. The report should clearly present the SE results and explain any design measures considered to improve sunlight access.

Visit All you need to know about scheme performance for the latest edition of BRE daylight and sunlight assessments for more information on sunlight exposure.

What are the design tips to improve the performance of a scheme?

There are a number of key things to consider from a design and layout point of view when it comes to improving daylight and sunlight assessment results. Each project is different, and the list below should be taken as a guide only. They include:

• Consider staggered balconies.
• Avoid recessed balconies with obstructing flanking walls.
• Consider reducing the depth of internal room layouts.
• Consider separation distances between blocks and neighbouring properties.
• Maximise window widths and heights but consider potential heat gains.

For more information on the above points, visit “An expert guide to daylight and sunlight assessments“.

When is a daylight and sunlight assessment required?

For many medium- and large-scale developments, a daylight and sunlight assessment is expected by planning authorities and forms an important part of a robust planning application. It is particularly necessary where a proposal could materially affect the natural light received by neighbouring buildings, gardens or amenity spaces, or where daylight and sunlight provision within the proposed development needs to be demonstrated.

The required scope will depend on the scale, height and massing of the proposal, its proximity to neighbouring properties and the relevant planning requirements. Establishing this early helps determine whether an impact assessment, a scheme performance assessment or both are required.

Should surrounding schemes be included to show cumulative effects?

Yes. It is very important that proposed schemes with extant permissions that are in close proximity to the subject site are considered in a cumulative assessment. Taking into consideration cumulative impacts can be complex and challenging, and each project is different. It is important, however, that you ensure that extant permission of neighbouring proposed developments is treated correctly under a daylight and sunlight assessment of the subject site, both from an impact assessment and scheme performance point of view.

Are compensatory design measures (CDM) important?

Yes. Where individual rooms or dwellings do not achieve the applicable daylight recommendations, the project team should consider whether reasonable design improvements can first be made. Where a shortfall remains, appropriate compensatory design measures and a clear design rationale should be provided.

Compensatory measures can include increased floor areas, greater floor-to-ceiling heights, dual-aspect layouts, improved outlook, enhanced private amenity space or access to high-quality communal and public open spaces. The appropriate response will depend on the nature and extent of the shortfall and the particular characteristics of the affected accommodation.

The architect will generally lead the design response, supported by the daylight and sunlight consultant’s analysis and input from the wider planning and design team. The report should clearly identify the affected rooms or units and explain how the proposed measures contribute to the overall quality and liveability of the accommodation.

If you need advice on your project with regard to daylight and sunlight, get in touch with our team, who will be more than happy to shed more light on your project! For more information on daylight and sunlight assessments, you can also visit the articles below or book a free presentation with the team by contacting us at info@3ddesignbureau.com or +353 1 2880186.

Is a daylight and sunlight assessment the same as a rights-to-light assessment?

No. Although both relate to access to natural light, they serve different purposes and are assessed separately. A daylight and sunlight assessment is generally prepared as part of the planning and design process. It examines how a proposed development may affect daylight and sunlight received by neighbouring buildings and external amenity spaces, as well as the performance achieved within the proposed scheme itself.

Rights to light is a separate private property matter relating to an established easement to receive natural light through particular windows or openings. It is a well-established consideration in UK development practice and can also arise under Irish property law, although it is encountered less frequently in Ireland.

A favourable daylight and sunlight planning assessment does not determine or resolve potential rights-to-light matters. Where such rights may be relevant, separate legal and specialist advice should be sought.

Keep reading on this topic:

• Expert insights on the latest BRE daylight and sunlight assessment guidelines
• All you need to know about scheme performance for the latest edition of BRE daylight and sunlight assessments
• An expert guide to daylight and sunlight assessments
• All you need to know about impact assessments for the latest edition of BRE daylight and sunlight assessments
• How to conduct a successful daylight and sunlight assessment
• Breaking down the jargon: daylight and sunlight assessments terminology
• A professional take on trees for daylight and sunlight assessments
• What’s new in the BRE guidelines 3rd edition 2022