Overshadowing, or loss of sunlight to existing premises, is analysed using annual probable sunlight hours (APSH). It is referenced within ‘Site layout planning for daylight and sunlight: a guide to good practice (BR 209)’.
APSH is used in planning and design stages to measure the impact to nearby existing buildings. The impact from local architectural shading features such as overhangs and balconies. Sunlight to gardens and communal open grounds.
Sunlight is a different term to daylight. Whereas sunlight studies measure access to the Sun, daylight studies measure luminance and illuminance resulting from the Sun.