Belfast·SPG004 Residential Extensions and Alterations·Page 41·4.3.21
Avoiding overshadowing of neighbouring properties
Extensions must be carefully sited and designed to avoid or minimise casting shadows that reduce a neighbour's daylight and amenity to unacceptable levels.
Where an extension is poorly sited or badly designed it can cast a shadow that may reduce a neighbour's daylight and adversely affect their amenity to an unacceptable level. It is important, therefore, that every effort should be made to avoid or minimise the potential for overshadowing to a neighbour when drawing up plans for an extension.
Source — /Users/richardhill/Documents/planning-arch-project/data/documents/belfast/SPG004 Residential Extensions and Alterations.pdf