We have an office project where perforated raft ceilings have been used, suspended from a concrete slab. Smoke detection has currently been installed in the void above; however, the perforations in the ceiling do not meet the requirements of BS 5839-1 2025 so this should be treated as a solid ceiling.
The following is an image of the ceiling which shows 150mm gaps between the raft sections.
We understand that detection will be required below the ceiling but should this be provided for each raft section on the basis that smoke would rise up between each raft, or is there an allowable gap between the rafts where they can be treated as a continuous ceiling?