And in the UK sheltered housing would generally be a place that is occupied as a domestic dwelling. It is a wholly self contained unit of accomodation, and (I believe) no judge could argue it is not occupied as a domestic dwelling. The common areas linking such flats up clearly come in to the RRFSO requirements, but the flat part is essentially the private dwelling of the person who lives there just as much as an apartment would be in a block of flats. The building regulations purpose group would usually be indicative of whether it is a residential dwelling, or whether it comes under "residential other", (Along with hotels, hostels, resi-care etc) and the standard of construction is quite different for each group.
The difference with hostels would be that they are usually not self-contained accomodation, the people inside them do not actually live there, the persons living there would not be paying council tax or having mail delivered there, and the fire alarm would usually be of a similar standard to a hotel. i.e. It would not be a stay put policy so there is no need for the sort of construction that is required to support a stay-put policy.
That being said, it is still a grey area, as Uratemp Ventures vs. Collins seemed to state that even a hotel room could be classed as a dwelling if someone was deemed to be living there. The matter that the person didn't cook their meals there was brushed aside, and the person in the room in question was essentially given the same rights as a tenant would have in a normal rental scenario. (This was not case law regarding fire safety, but just aimed at tenants rights)
We should also bear in mind that no matter how sure we are of whether the RRFSO applies or not, and building regulations purpose groups aside, it only takes some half-witted magistrate a mis-informed magistrate to throw a spanner in the works and 'declare' such premises as domestic without considering how the premise was built. (No reference to actual historical decisions by magistrates is intended here) Some times if there is any doubt, the only way forward for an FRS is to try and enforce their 'will', and leave it to the appeals process to decide.