Graeme,
On a new build sheltered housing scheme the dwelling units would normally be treated as self-contained flat (in most situations). As self-contained flats, the requirement would be to provide a mains wired smoke detector in each unit (part 6 system). Detection may be provided in the common areas but only to activate AOVs (if required) therefore for a code compliant sheltered housing scheme the requirements in terms of detection are minimal.
I have seen many schemes that have detection within each unit that is linked back to a wardens central monitoring system and additionally have detection in the common areas. However these are over and above the requirements of the Building Regulations and are often provided as part of a good management plan and in recognition of the vulnerability of the occupants. (Elderly and often in need of assistance)
You say your scheme does not have detection in the kitchen, this seems like a reasonable approach to prevent false alarms, however a heat detector would also help prevent false alarms and provide some additional protection.
It is not possible to say detection is or is not required in your scheme because it may be that the layout of the units, common escape, compartmentation, etc etc are at odd with the guidance for new self-contained flats. The detection may be a compensatory feature for lack of provision elsewhere. If this the case then the level of detection becomes very subjective.
