Daylight and building design - European Standard EN-17037
Does new legislation mean we can stop leaving the lights on? asks RPS Principal Consultant Rallou Nikolaou
Daylight is proven to have a multitude of benefits including for health, wellbeing and mood. It is therefore an important and desirable factor for buildings; particularly in dwellings or any space people tend to occupy for long periods of time, such as work places.
Daylight levels in such developments are currently subject to local and national guidance; however, UK-wide legislation - incorporated into Building Regulations - has been lacking. Instead, the BRE Guide 'Site layout planning for daylight and sunlight: A guide to good practice' is widely accepted and used to determine planning applications.
Recognising this gap, the first daylighting European Standard EN-17037 ‘Daylight of buildings’ was officially published and came into effect in December 2018. This specifies minimum recommendations for new developments covering daylight provision, view out, exposure to sunlight and protection from glare.
The new standard requires a median daylight factor of 2.1%. Compared to current recommendations this means that an Average Daylight Factor (ADF) of around 1.5 times higher would be required for compliance.
This is likely to be difficult to achieve, especially for dwellings in dense urban areas where basements or conversions are common. Architects would need to further optimise designs through glazing and internal layouts to achieve it, causing a potential increase in design costs and / or reducing achievable development densities and hindering housing delivery.
To address this, a National Annex is currently being drafted to accompany the EN Standard and set alternative target values and methodologies to apply in the UK. Once completed, there will be a re-write of the BRE Guide; currently heading for a publication date of 2020.
These changes have the potential for a big effect on the residential sector and may require the design process to undergo a considerable shift. It is thought that only around 30% of current dwellings in the UK would comply under the new standard.
However, with no clear timeframes there is a sense of ambiguity over when the new European Standard will become part of planning policy; creating uncertainty that could lead to different planning applications being approved or rejected despite having similar designs and meeting the same requirements.
Developers should ensure daylight is integrated into the very first stages of the design process and so it will become increasingly important to liaise with a good planning consultant, architect and sustainability consultant in the early stages; especially on projects where planning applications are not expected until after 2020, due to the risk that current design will not meet future requirements.
The increase in daylight will need to be considered in conjunction with energy usage and risk of overheating. If not managed correctly, the additional glazing can cause unwanted solar gains and heat losses, affecting both the energy performance and thermal comfort of a building.
The publication of this new standard dedicated entirely to natural lighting is good news for the building sector. Even if it is very ambitious it will support and force a renewed interest in daylighting from designers, authorities and developers.