25 degree rule for dwelling siting

In terms of the 25 degree rule, new dwellings should be sited so as not to result in a 'subtended angle' of more than 25 degrees of a line projected from the centre point of the lowest main habitable room window at ground floor level, when drawn in section detail perpendicular to the main façade of the proposed property. Overshadowing is more of a problem on sloping sites and therefore greater spacing is required. Therefore on sloping sites a mid-point 2m above ground should be taken.