Office ceilings

[Guest lston]

I've always been under the impression that a commercial premise (office space) should have a 30 minute fire resistant ceiling even when in a multi storey block  unless it is below residential premises obvioulsy.

Am i right in thinking this as ADB has confused me

[AnthonyB]

P66 8.11 points out they don't need to be compartment floors, but Table B4 does give a 30 minute fire resistance requirement even when not a compartment floor. Of course the age of the building will have an impact on what was required at the time it was built.

 

[Lyledunn]

It is not the ceiling that is required to be fire resistant but the floor as a composite, a subtle but important difference. I often hear builders ask about how many sheets or what thickness of PB is needed to provide a certain fire resistance without understanding the element should be treated as a composite.
In purpose group 3 compartmented floors are not required but elements of structure, like floors, are required to be at least 30min REI depending on height. 
It is not unusual for purpose groups to change in multi-storey office buildings. We are involved in a conversion at the moment where ground and first of a recently constructed office block will become a cocktail bar and restaurant. Careful planning will give building owners better flexibility.