Southwest Environmental Limited

ADF Daylight Assessment

Whilst BR209 for the most part concentrates on impact on neighboring properties, there is some consideration given to the lighting levels within the proposed development.

There are standards set for average daylight factors which are: 1% for bedrooms and 2% for kitchens and living rooms. In many cases Local Authorities, particularly London Borough Planning Authorities will pick higher values.

Some councils such as Plymouth rely on Window Size to Floor Area comparisons, which is also quite effective.

The ADF value is created by "blending" together Internal Walls Areas, Glazing transparency, Open Sky Angle and Surface Reflectivity.

We are typically asked to do these for basements, or lower ground floor proposals.  Image: David Lally, via Wikimedia Commons

The truth is that if you have a moderately sized window, that is not too badly "over shadowed" it is very likely that your room will pass, the ADF Assessment. Problems arise during retro fit projects, particularly where there are light wells, or glazed grates where there is a very narrow open sky angle, and this has a negative effect on calculations.

If you have been asked to check daylight levels in a proposed development then please get in touch, and we can have a quick look at plans and tell you what the score is.