Ruth Kelly Waskett, Principal Daylight Designer
Exploring the impact of the new European daylight standard.
The new European daylight standard (EN 17037) was quietly published last month. It’s been 10 years in the making, and is the first pan-European standard on daylight in buildings.
The lack of fanfare might be understandable given the current uncertainty surrounding the UK’s relationship with the EU. Nonetheless, the UK plans to adopt the standard; a process which is expected to take several months. Ahead of this, I wanted to explore what the new developments are, and what they might mean for our clients.
Its publication signals the increasing importance of daylight in buildings, not just as an energy-saving feature, but as a characteristic of healthy buildings.
The standard also comes at a time when climate-based daylight modelling has become more mainstream, but is not always possible e.g. on small building projects with limited design resources.
This new British Standard is likely to replace BS 8206-2, the Code of Practice for Daylighting (2008). So, how does it differ from what we currently have in place? Well, one of the main developments is that it gives daylight targets in terms of illuminance as well as daylight factor. In essence, this means we can use either climate-based modelling or daylight factor calculations to work out the levels of daylight in a building. This is good news for clients who want to achieve building energy certification with a scheme such as WELL, which requires climate-based daylight modelling to demonstrate compliance.
This flexibility is a theme that runs through other aspects of the new guidance. It also provides a mechanism for adjusting daylight factor targets to suit the geographical location of a building, and therefore the daylight availability at a given site.
Added to this, there are now high, medium, and low daylight targets, rather than a one-size fits all approach. This means different types of building, with different activities going on inside them, can be taken into consideration, and daylight levels assessed accordingly.
The new standard is also quite rightly concerned with limiting sunlight exposure in order to avoid overheating in a space. It gives sunlight exposure targets in terms of duration of exposure to sunlight on the equinox (21 March) under low, medium, and high exposure targets. Again, this is useful because it allows designers and clients to apply different criteria to different types of building depending on their use and the needs of occupants.
In recognition of the fact that good daylighting is about more than daylight quantity, the new standard provides quantitative guidance on views out of a building and glare.
The criteria for views out are based on the distance of a viewer from a window and the size of the window, creating a view angle. The glare criteria are based on the Daylight Glare Probability (DGP) metric, an index which has become widely regarded as the most reliable daylight glare metric.
I believe the impact of this new standard will be significant for those tasked with predicting daylight in all kinds of buildings, but particularly residential. Currently, planning applications for residential developments often require an internal daylight assessment providing evidence for adequate daylight provision in habitable rooms. Most local authorities refer to BRE guidance, which is itself based on BS 8206-2.
The new standard will look and feel very different, and it will take time for everyone to become familiar with it.
It will also be interesting to see how other European countries handle the transition. There are bound to be teething pains when the standard starts to be applied on real projects, especially if consultants and local authorities interpret the guidance in different ways.
For the moment, though, we look forward to the new British Standard in a few months’ time – watch this space!