The BRE guidance includes various initial ‘rule of thumb’ tests which should be used to determine whether there is a risk that the development itself or neighbours to it might be at risk of receiving inadequate natural light. Failure of these initial assessments would be the trigger for a Local Authority to ask the developer for a more detailed full consideration of the potential effects of a development in respect of daylight and sunlight. Normally, this more detailed assessment would involve 3D CAD modelling and the use of specialist software.
Some common misconceptions include Councils who request the Daylight and Sunlight Tests for all proposed 2-storey (or taller) developments within 2m of the boundary. This is an example of an incorrect approach which could lead to the request for such assessments when this is not necessary or, conversely, failure to ask for the Daylight and Sunlight tests when they should be requested from the developer.
It should be borne in mind that, potentially, inadequate consideration of these Daylight & Sunlight Tests in respect of an application for planning permission could leave a planning permission open to the risk of legal action by means of a Judicial Review.