F3Any works to or in a building F4... that is a prison or a building where a person may be legally detained or otherwise legally held in custody. Except – Any work which increases the floor area of the building by more than 100 square metres. Any demolition or alteration of the roof, external walls or elements of structure. Any work involving underpinning. Any work adversely affecting a separating wall. Any work involving a change in the method of wastewater discharge. Work, not being work of types 3 to 26 below, to a prison or a building where a person may be legally detained or otherwise legally held in custody having a storey, or creating a storey, at a height of more than 7.5 metres.