For the purpose of fixing Siniat Plasterboard direct to the underside of a timber ceiling, there are two scenarios which will dictate the need for noggings. 

In cold state - where the ceiling/floor element is not required to have a fire resistant period the following recommmendations can be followed:

In hot state - where the ceiling is required to have a fire resistance period, it will be dependant on the supporting fire test data. The advice above will be superceded if the system in question was tested with noggings which will then be necessary to perimeters, around obtrusions and between joists irrespective of board type and joist centres.

Boarding pattern to the timber joist/noggings as below: