New European Standard for Daylighting ( EN17037 )
Following the British Standards Institute’s consultation on a new European daylighting standard last year, the CIBSE Daylight group have revealed the proposed changes.
The new European Standard for Daylighting, or EN17037 was published in December 2018 and considers several factors such as sunlight, view and glare. The most interesting part of EN17037 for Daylight & Sunlight surveyors are the proposals for daylight assessments of proposed new developments.
The new standard recommends specifies minimum levels of daylight as follows :
• An illuminance level of at least 300 lux over at least 50 % of the space for at least half of the daylight hours in the year; and
• An illuminance level of at least 100 lux over 95 % of the space for at least half of the daylight hours in the year.
To meet the proposed new standard a median daylight factor of 2.1% will be required.
The current standard (BSI 8206 Part 2) recommends the calculation of an Average Daylight Factor (ADF) which equates to approximately 1.5 times the median daylight factor. This means that an ADF of about 3.2% would be required to achieve the new minimum standard proposed, a much higher target than the greatest requirement in the current standard of 2% ADF for a kitchen.
This increased requirement will be particularly problematic when designing for daylight in denser urban areas such as London, where daylight availability for existing buildings is lower than the new standard proposed. To address this concern CIBSE and the BRE (Building Research Establishment) have been tasked with proposing a National Annex which would set alternative target values and methodologies to apply in the UK. The current proposals being considered are as follows :
• Adopt the minimum ADF target criteria in BS8206 Part 2
• Adopt EN17037 methodology for assessment but use lower target median daylight factors
• A combination of the above.
Most local authorities refer to the BRE guidelines (Site Layout Planning for Daylight and Sunlight – A guide to good practice 2011) when assessing the quality of daylight & sunlight in a proposed new development. The BRE hope to secure funding and re-write the BRE guidelines in the financial year beginning April 2019, with the view of a revised publication in 2020. These timescales leave a fair degree of ambiguity as to when the new European Standard will become part of planning policy and what the transition between standards will be.
With the drive to increase the supply of new housing without infringing the Green Belt, it remains to be seen whether the new standard and National Annex will provide an improvement when designing for daylight and in delivering much needed housing in increasingly dense urban areas.
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