The Third Edition of the BRE Guide “Site layout planning for daylight and sunlight: a guide to good practice” was published in June 2022 and replaced the previous edition from 2011. The BRE Guide provided guidance on the assessment of daylight and sunlight impacts and provides recommendations on levels of internal daylight and sunlight. The BRE Guidance is the methodology that underpins all daylight and sunlight assessments.
What’s different?
The revised guide remains fairly unchanged when it comes to looking at daylight impacts on neighbouring properties. Other than a few clarifications, the method is the same as the 2011 guide, with the Vertical Sky Component, No-Sky Line and Annual Probably Sunlight Hours all still the main daylight and sunlight criteria. However, regarding the adequacy of natural daylight within the proposed rooms, the guidance has changed considerably. The new BRE guidance now reflects the guidance contained within BS 17037, published in 2019.
BS 17037 changes the way that daylight within dwellings is considered. It provides two methods for looking at internal daylight, both of which are now in the Third Edition of the BRE Guidance. The first method is the daylight “illuminance method”, which considers the amount of illuminance (in Lux) across the room, taking into account Climate Based Daylight Modelling (CBDM). The second, less complicated method, is the “Daylight factor method”. This method which requires a target daylight factor to be exceeded over half of the room.
The new tests replace the previous Average Daylight Factor (ADF) and No-Sky Line (NSL) tests from BS 8203 and the old BRE Guidance. The ADF test was used to assess the average level of light across a whole room. The NSL test was used to determine how evenly the daylight was distributed. Now, instead of looking at the average daylight factor, the new method considers the median level of daylight across a room. This therefore replaces both ADF and NSL with one test.
What does this mean for developers?
So the question we have been asked is “are the new daylight standards in the BRE guide more difficult to achieve”? The answer is they probably are. However, as the ADF and the new Daylight Factor are calculated using different inputs. The new and old tests are not directly comparable, i.e. you can’t convert one to the other. However, it is likely that in many situations, a higher ADF would be required to achieve compliance with the new standards.
Since the ADF took the average level of daylight across the room, one could make a room comply with very high levels of daylight by the windows. This would compensate for gloomy areas to the rear. However, as the new Daylight Factor method looks at the median Daylight Factor, one needs to ensure that reasonable levels of daylight are provided over much larger areas of the room. Consequently, the amount of glazing a room requires is not the only factor in room design for daylight. Window position is also now a very important factor.
The new BRE Guidance also considers glare and view in greater detail to the previous version of the guide. The new guidance also considers the impacts to solar panels for the first time.
If you would like any more information about the new BRE Guidance or to discuss any other daylight issues, please get in touch.