3D Design Bureau

Guidelines and standards for daylight and sunlight assessments can be difficult to navigate. With several different standards in use, it can be challenging to determine which guidelines are most relevant and what constitutes best practice.

This blog explains, as clearly and simply as possible, the main BRE daylight and sunlight guidance and associated standards, including BRE 209, BS EN 17037, its UK National Annex, and I.S. EN 17037, how they relate to one another, and what should be considered best practice.

Note: The primary guiding document for a comprehensive daylight and sunlight assessment is BRE 209 (third edition). For daylight provision within proposed dwellings, the guidance refers to BS EN 17037 and its UK National Annex, using an illuminance-based approach in place of the average daylight factor (ADF) method referenced in the previous edition. EN 17037 and its Irish adoption, I.S. EN 17037, also provide standards for daylight within buildings and may be relevant depending on the location and scope of the assessment.

The BRE daylight and sunlight guidelines 2011 (edition 2)

Up until June 2022, the second edition of BRE 209, published in 2011, was the main guiding document for daylight and sunlight assessments in Ireland. This version of the guidelines referenced the British standards – BS8206 when it came to target values of the old metric of assessment known as average daylight factor (ADF).

Both the BRE guidelines 2011 and BS 8206 standards were referenced in a number of Irish Government guidance documents, including:

• Urban Development and Building Heights: Guidelines for Planning Authorities (2018). This guidance continues to reference BRE 209 (2011) and BS 8206-2:2008, although both documents have since been superseded.
• Sustainable Urban Housing: Design Standards for New Apartments. Previous editions of these guidelines also referenced BRE 209 (2011) and BS 8206-2:2008. These apartment guidelines have since been replaced by the Design Standards for Apartments, Guidelines for Planning Authorities (2025).

The European Standards, EN 17037 – Daylight in buildings

EN 17037 – Daylight in buildings was first published in 2018, followed by the Irish adoption of the standard, I.S. EN 17037. The Irish standard follows the European standard without changes to its daylight provision criteria. The current amended version is I.S. EN 17037:2018+A1:2021. Both standards state very high lux level target values for daylight within buildings. They are considered very onerous within the industry, but proposed developments in Ireland should still be assessed for SDA under IS-EN 17037.

The UK standard, BS EN 17037, and its National Annex

Soon after the publication of EN 17037, the UK adopted the European standard as BS EN 17037. The UK version includes a National Annex which provides alternative recommendations for daylight provision within dwellings.

These recommendations use lower target illuminance values than the general European criteria and vary according to room type, with separate targets for bedrooms, living rooms and kitchens. This room-specific approach is particularly relevant to residential developments and is referenced by BRE 209 when assessing daylight provision within proposed dwellings.

The BRE daylight and sunlight guidelines 2022 (edition 3)

The third edition of BRE 209 was published in June 2022. Among a number of key changes was the reference to BS EN 17037 for daylight provision within buildings and rooms, using illuminance-based target values, rather than the BS 8206-2 average daylight factor (ADF) method referenced in the previous edition. For projects in Ireland, I.S. EN 17037 should also be considered where relevant to the scope of the assessment and applicable planning requirements.

For a full list and explanation of the main changes between the BRE 209 (2011) and BRE 209 (2022), see “What’s new in the BRE guidelines 3rd edition 2022″.

It is the opinion of 3D Design Bureau, that the best practice when it comes to following guidelines is to produce your primary assessment under the BRE 209 (2022), which references the BS-EN 17037 standards, but to also publish results for IS-EN 17037 and give compliance rates under both sets of standards. It is very important that daylight and sunlight assessments that are following BRE 209 take into account existing and proposed trees within their assessments, as they can have an impact on results. For full information and explanation as to how and when to include trees in a daylight and sunlight assessment, read here: “A professional take on trees for daylight and sunlight assessments”.

Irish national planning guidance has also evolved since the publication of the third edition of BRE 209. The Sustainable Residential Development and Compact Settlements Guidelines for Planning Authorities identify I.S. EN 17037, the UK National Annex to BS EN 17037 and BRE 209 as relevant quantitative approaches where a technical daylight assessment is required. The Design Standards for Apartments, Guidelines for Planning Authorities should also be considered for apartment developments, alongside any applicable requirements of the relevant local planning authority.

It is important to note that BRE 209 and the associated standards should not be treated as rigid planning pass-or-fail criteria. They are all considered advisory documents. The BRE guide is preceded by the following very clear statement as to how the design advice contained therein should be used:

“The advice given here is not mandatory, and the guide should not be seen as an instrument of planning policy; its aim is to help rather than constrain the designer. Although it gives numerical guidelines, these should be interpreted flexibly since natural lighting is only one of many factors in site layout design.”

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.

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