There is a domestic flat which the building lets out. Should the fire alarm system have fire sounders from the offices in the domestic premises? And should the premises have automatic fire detection that informs the offices of fire from the flat?

TD

Yes & possibly. Sounds like the old caretakers flat in a late 20th century building.

A fire in the office block would have a major impact on the life safety of the flat.

The flat as a minimum would need a self contained LD3 system to BS5839-6 plus some sounders from the main building system. There would not be an automatic need for main building detection inside the flat (cover to the stair landing outside the front door would do) but would have property protection benefits.

Found out the flat is not let out but houses staff and/or visitors from foreign offices from time to time. Would a L1 or L2 system be needed due to the occupancy being staff??

You could provide that type of coverage as an alternative to the mixed system set up above.

I would favour AB's first suggestion as you wouldn't want a false alarm (burning the toast) instigating the general fire alarm, but as well as extending the the sounders would provide a heat detector in the hallway of the flat to warn the remainder of the building if there is a genuine fire in the flat.