Solid masonry separating wall - ceiling void and roof space junction

In the case of the junction between a solid masonry separating wall type 1 and the ceiling void and roof space, the solid wall need not be continuous to the underside of the structural floor or roof provided that – (a) there is a ceiling consisting of two or more layers of plasterboard, of minimum total mass per unit area 20 kg/m2; (b) there is a layer of mineral wool (minimum thickness 200 mm, minimum density 10 kg/m3) in the roof void; and (c) the ceiling is not perforated. The ceiling joists and plasterboard sheets should not be continuous between rooms for residential purposes (see Diagram 6.1).