Its in all of the higher risk residential building
421.1.7
Arc fault detection devices conforming to EN62606 shall be provided for single phase AC final circuits supplying socket outlets with rated current not exceeding 32A in:
• Higher risk residential buildings
• Houses of multiple occupancy (HMO) • Purpose built student accommodation • Care homes
NOTE 1: Higher Risk Residential Buildings are assumed to be residential buildings over 18m in height or in excess of six storeys, whichever is met first. It is anticipated that in many areas, higher risk residential buildings will be defined in legislation which can be subject to change over time, as well as in risk management procedures adopted by fire and rescue services. Current legislation should be applied.