Your expected tenants can have a massive impact on design both cost and level of cover, this is all clearly set out in the standards, I just done a series of flats for ex addicts, crims etc and had to do a system that accounted for their condition, it added about 4k to the job but my arse is covered.. most people think there insurance will be a fall back but that will not help if they haven't followed the standards nor agreed with the local fire service and building control.. for the insurance firms any slight deviation from the regulations will void cover unless all parties agree on the design.