3D Design Bureau

Guidelines and standards for daylight and sunlight assessments have been very confusing over the past number of years. This is because, particularly in Ireland, reference to now superseded daylight and sunlight documentation still remains in some government guidelines for property development. Furthermore, with various different standards in play, anyone could be forgiven for not being able to follow what is best practice when it comes to what guidelines and standards to follow.

This blog explains, as best and as simply as possible, the BRE daylight and sunlight guidelines and standards to follow and what should be considered best practices.

Note: The primary guiding document for a comprehensive daylight and sunlight assessment is the BRE Guidelines (BRE 209 – 2022) These guidelines reference the BS-EN 17037 standards for target levels of internal daylighting within buildings (formerly ADF and now SDA). Both the European standards (EN 17037) and their Irish adaptation counterpart, the IS-EN 17037, are different standards with higher target levels for internal daylighting in buildings.

The BRE Daylight & Sunlight Guidelines 2011 (edition 2)

Up until June 2022, the BRE Guidelines 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 are/were referenced in the following Irish Government documents:

• Urban Development and Building Heights, Guidelines for Planning Authorities. No recent update and both BRE 209 (2011) and BS 8206 are still referenced within.
• Sustainable Urban Housing: Design Standards for New Apartments ~2018 & updated in 2020. This document is now superseded by the 2022 version released in December 2022. It references the more up-to-date BRE Guidelines edition 3 and standards such as BS-EN 17037 and IS-EN 17037. The previous 2018 & 2020 referenced the BRE Guidelines 2011 and BS 8206 standards.

The European Standards, EN 17037 – Daylight in Buildings

In circa 2018, The European Standards, EN 17037 – Daylight in Buildings, was published and soon after the Irish adaptation of these standards, IS-EN 17037 was released. It should be noted that the Irish adaptation is in effect the European standards as no changes were made from that of the EN 17037. 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 British Annex to the European Standards BS-EN 17037

Soon after the publication of EN 17037, the UK recognised the onerous nature of these standards and produced a British Annex to the European Standards, the BS EN 17037. They made changes to the EN standards reducing target lux values to less onerous levels. They also identified different target lux level values depending on the room type, something that EN 17037 does not do. These are the main standards that the BRE Guidelines edition 3 reference.

The BRE Daylight & Sunlight Guidelines 2022 (edition 3)

The long-awaited update to the BRE Guidelines landed in June of 2022. It is still referred to as BRE 209. Amongst a number of key changes was the reference now to the BS-EN 17037 standards for daylighting within buildings/rooms (lux levels) as opposed to the old BS 8206 standards. It is important to note that the new BRE 209 also makes reference to the IS-EN 17037 and therefore, in Ireland, a supplementary assessment under these standards should be included in daylight and sunlight assessment reports. 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 3DDB, 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

Since the publication of BRE 209 (2022) Irish government and local planning authority documents have been updated. These include Sustainable Urban Housing: Design Standards for New Apartments and Dublin City Council development plan 2022-2028. Both documents now reference BRE 209 (2022) along with the BS EN 17037 and IS-EN 17037 standards.

It is important to note that neither the British Standard, European Standard, British Annex to the European Standard nor the BRE Guide set out rigid standards or limits. 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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