hallbo

Hello I am working in victorian property that was converted into three flats in 1986. It has a communal hallway and there are three flats over three floors. The FRA has confirmed that a Grade A LD2 system is to be fitted along with other upgrades to the hallway fire protection. Heat detectors will be fitted into each flat but I was told by a tenant that they should be fitted in the kitchens but this would involve long cable runs across the very ornate plaster ceilings. Running the cabling in the ceilings /under the floors of the flat above is restricted by solid oak flooring and surface mounting seems the appropriate installation method. Each flat already has its own independent smoke detection (240v with battery back up) and I seem to remember that the heat alarms could be fitted on the ceiling inside the flat as long as they are away from the entrance(1000mm)? I have tried to find the guidance unsuccessfully but I am sure that the wealth of knowledge on the site will know, or will tell me where to find the answer. Thanks Garry