These ceilings are considered as part of the whole system (roof/slabs + ceiling) and the fire classification is valid only for the entire load-bearing construction (identical or similar to the one tested). So the rating is achieved by the entire system, which is both the structure above as well as the suspension or fixing mechanism and, finally the lowest membrane or ceiling.
In this case the ceiling is defined as “lining plus any supporting framework, including hangers, fixings and any insulation material”.
The ceiling may be attached directly to the structural member or suspended from it or be self-supporting. If it’s suspended, extremely important is the height of the cavity (the space between the upper surface of the ceiling and the underside of any floor, roof or its supporting construction) which must be at least high as the one tested: it’s possible to increase it but not decrease it.
The complete roofing system, including the ceiling, is tested for integrity, insulation and loadbearing capacity (REI) and with respect to the structural building member, the maximum moments and shear forces shall not be greater than those tested.
No combustible or insulating material can be added to the cavity, unless the same amount (in term of fire load) was included in the fire test.
In Europe these roof or floor systems are tested according to EN 1365-2.
Typically, such systems achieve up to 120 minutes fire resistance (REI 120) or up to 180 minutes (REI 180) for concrete slabs.
IMPORTANT: the contribution to the fire resistance is valid only if the system is installed exactly as in the fire tests, including hanging (suspension system), junctions between membrane and walls/ edge panels, joints and jointing materials.