45 Degree Angles Test for Daylight Assessment

For adequate levels of daylight to be maintained, extensions should therefore be designed so as not to cross a line projected from the midpoint of an adjacent neighbour's/ neighbours' nearest main habitable rooms window(s), perpendicular to the proposed extension in both plan and elevation view. The steps to be followed are as follows: i. Locate the midpoint(s) of the closest main habitable room window(s) of the neighbouring property/ properties. ii. In plan and elevation views draw a line/lines from the midpoint of the required window(s) at the 45 degree angles, as per above, and as shown in Figure 4.14. In applying the angles tests 45 degree lines are used for all extensions and are taken from the mid-point of the closest neighbouring main habitable room window(s) at ground floor level. The only exception to this is when a two-storey extension is proposed and one or more of the closest neighbouring main habitable room windows is located at first floor level. In such instances 45 degree lines can be drawn from the mid-point of the relevant first-floor window(s), and where applicable, any main habitable room window located on the ground floor of any other neighbouring property. NOTE: The 45o angle must only be taken from first floor level in instances where the closest neighbouring main habitable room window is at this level and where the proposed extension is two storey. In all other cases the 45o angle must be taken from the closest neighbouring main habitable room at ground floor level.