In timber frame structures stone wool is used as thermal, fire and sound insulation. Surface materials such as plaster board form an air-tight layer that prevents combustion gases from moving through the structure during a fire. The amount of layers of plaster board also affects the fire resistance of the structure.
Use PAROC stone wool in attics to increase the fire resistance. In this case, you can even leave out some of the plaster boards to reach the same fire classification. For this solution, try PAROC eXtra or PAROC BLT.
According to the Knauf certificate (VTT-C-2947-08), a roof structure with 150mm PAROC eXtra and (i.e., two layers of Knauf KN13) plaster board in the ceiling achieves the fire classification REI 60.