3D Design Bureau

What’s New in the BRE Guidelines 3rd Edition 2022

Unpacking the Key changes to Daylight and Sunlights assessment with the release of the updated 3rd edition of the BRE Guidelines in June 2022.

In June of 2022, the BRE Guidelines for daylight and Sunlight assessment (BRE 209) was updated to its 3rd edition. Up until then, assessments were following the guidance of BRE 209 (2011). With the publication of the new edition came a number of key changes to how daylight and sunlight assessments are to be carried out and some new assessment metrics were introduced.

For a more detailed insight into daylight and sunlight assessments you can book a free presentation with 3DDB by clicking this booking link – Free Daylight and Sunlight Assessment Presentation (Online)

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Internal Daylighting in Buildings

One of the most significant changes to occur with the publication of the 3rd edition of the BRE Guidelines was the change of assessment metric for internal daylight within buildings. Up until the release of the BRE 209 (2022), the metric assessed was Average Daylight Factor (ADF). This has now changed to illuminance lux levels, otherwise known as Spatial Daylight Autonomy (SDA) or Median Daylight Factor (MDF). SDA measures the amount of lux levels within a room. For daylight and sunlight assessments, habitable rooms are assessed. Furthermore, target lux level values are taken from the BS-EN 17037 as opposed to the BS 8206 which BRE 209 (2011) referenced. It should be noted that the BRE 209 (2022) also makes reference to the IS-EN 17037 for target values. For full details on this new metric of assessment, and more, visit All you need to know about scheme performance for the latest edition of BRE Daylight and Sunlight assessments

BS-EN 17037 for daylight and sunlight assessment
BS-EN 17037 for daylight and sunlight assessment

Reflectance Values

Reflectance values in daylight and sunlight assessments are the numerical values applied to surfaces that dictate the amount of natural light that is reflected and absorbed by that surface. The darker the material, the lower the numerical value and the less reflective it is.

Within every digital 3D analytical model, surfaces with different finishes should be identified. Then within the assessment process, reflectance values should be assigned to these surfaces. Depending on the reflectance value of the internal and external surfaces of a building, including the site finishes such as paving, grass, etc, the higher or lower the daylight values will be within an assessed room. 

The BRE Guidelines (BRE 209 – 2022) have stated reflectance values that are in line with the lower levels stated in the European standards EN-17037 and Irish adaptation to the European standards, the IS-EN17037. These are to be used unless ‘otherwise specified’ by the design team.

Glass Transmittance

Glass transmittance values should be applied to all glazing of assessed units. Under BRE 209 (2022), their properties should be 0.68 unless ‘otherwise specified’ by the design team. The lower the numerical value the less natural light will penetrate into the room.

Averaging of windows in Impact Assessment

Under BRE 209 (2022), windows that are being averaged out on impact assessments must be weighted. This means where two windows of non-equal size are servicing the same space, this factor must be taken into consideration in the calculations. Furthermore, where windows servicing the same space are more the 5 meters apart, they are not to be averaged and should be tested individually with the level of impact stated for each.

Impact assessment for the BRE daylight and sunlight report

Sunlight Exposure (SE)

Sunlight Exposure (SE) is a new metric introduced in the BRE 209 (2022). It is the assessment of sunlight in the habitable rooms of a proposed development. All habitable rooms should be tested for SE and levels are given for each room. Under the BRE Guidelines, where one room in a residential unit meets the minimum recommended levels of sunlight exposure, the unit as a whole is considered to have passed. However, the BRE Guidelines does state that the room in question should preferably be a living room.


Trees are now to be included in daylight and sunlight assessments. Whilst it does add a layer of complexity to studies, it is important to consider them. Assessments should include existing and proposed deciduous and evergreen trees. For full details on how trees should be included in daylight and sunlight assessments visit A professional take on Trees for Daylight and Sunlight assessments

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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Nicholas Polley - Managing Director at 3D Design Bureau


Nicholas Polley
Managing Director
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