3D Design Bureau

Expert answers to the top 10 FAQs on Daylight and Sunlight Assessments

This blog provides answers to the top 10 FAQs for daylight and sunlight assessments. As the criteria for daylight and sunlight assessments have changed so much over the past number of years, and reports have become far more complex, it’s no wonder why there are so many questions to answer, not to mention the confusion amongst clients and design teams. The quantity of assessments to be carried out has also increased significantly leading to more data being captured which in turn leads to more explanation.

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.

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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) 2022. 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 Latest BRE Daylight & 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 for the latest edition of BRE Daylight and Sunlight assessments AND All you need to know about Impact Assessments for the latest edition of BRE Daylight and Sunlight assessments

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

Yes absolutely. It is not a straightforward workflow and different tree states should be included for different metrics. 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?

Up until the release of the 3rd edition of the BRE Guidelines, compliance rates were given for schemes. Compliance rates for ‘Impact Assessment’ and ‘Scheme Performance’ should still be stated in reports. However, nowhere in the BRE Guidelines (2011 or 2022), or other guidelines and standards does it state specific target compliance rates for the various assessments. Despite this, some design teams and planning authorities are led to believe there are target values for compliance rates to be hit.

Whilst proposed schemes should try to achieve as high compliance rates as possible it should be noted that there is NO specific target value to achieve. It is up to planning authorities to consider daylight and sunlight reports in conjunction with other planning submission reports and documentation and make an informed decision on the application. 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)?

NO and for the same reasons as listed above for Scheme Performance. Sunlight Exposure (SE) is a new metric under BRE 209 (2022). However, daylight and sunlight reports should state compliance rates. Will target rates be expected? only time will tell! 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.

Are planning authorities and An Bord Pleanala up to speed on the new guidelines?

Evidence would suggest they are not. They grappled to get a good understanding of previous guidelines and just as that was happening the BRE 209 was updated to its 3rd edition in June 2022. Education across the industry is key and something that 3D Design Bureau is trying to carry out with free daylight and sunlight assessments. You can book a free presentation with the team by contacting us at info@3ddesignbureau.com or +353 1 2880186

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 neighboring properties.
  • Maximise window widths and heights but consider potential heat gains.

For more information on the above points visit Daylight & Sunlight Assessments: A Vital Component to Planning Applications.

Are there any future changes expected with regard to Daylight & Sunlight Assessment?

The answer to this is ‘time will tell’. So many changes have happened over the course of the past number of years it would be naïve to think there won’t be any more changes. It is hoped that with the publication of the BRE 209 (2022) and the recent updating of some Irish government guidelines and documents in December 2022, things should settle down. However, if history is anything to go by, future planning decisions or opinions along with rulings on Judicial Reviews that reference daylight and sunlight of a planning application could move the goalposts yet again.

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 neighboring 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. Compensatory design measures should be stated for any units that are underperforming from a daylight point of view. CDMs are stated as a requirement in the Irish apartment guidelines and the best practice is to state them for each individual unit that is failing to meet the minimum standards as per the BRE Guidelines. Where individual CDMs cannot be given, a proper compensatory design rationale and justification should be provided as a minimum. CDMs are the responsibility of the project architect.

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
at 3D Design Bureau


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