All flats require, under the Building Regulations 2013, to have boundaries (ie walls and floors) possessing one hour fire resistance. This is assessed in a severe furnace test BS 476 Part 8 or equivalent BS EN and the furnace fire severity represents fire after flashover in a room with combustion gas temperatures rising to 1000 degC. The question here was ‘Does the offset party wall and floor construction provide one hour separation between flats as required under building regulations?’