Cavity barriers in cavities over undivided rooms exceeding maximum dimensions

Where the cavity is over an undivided room which – (a) exceeds the appropriate maximum dimension for a cavity in Table 4.7, cavity barriers need only be provided on the line of the enclosing walls of that room, provided that they are not more than 40 m apart and that the surfaces exposed in the cavity are not lower than Class 1 (National class) or Class C-s3,d2 (European class); or (b) exceeds 40 m (in either direction on plan), cavity barriers need not be provided where – (i) the room and the cavity together are compartmented from the rest of the building; (ii) an automatic fire detection and fire alarm system complying with BS 5839-1 is fitted in the building; (iii) the surface of the ceiling exposed in the cavity is of Class 0 (National class) or Class B-s3,d2 or higher (European class) and the ceiling supports and fixings in the cavity are of non-combustible construction; (iv) the surface spread of flame classification of any pipe insulation in the cavity is not lower than Class 1 (National class) or Class C-s3,d2 (European class); (v) any electrical wiring in the cavity is laid in metal trays or in metal conduit; (vi) any other material in the cavity is a material of limited combustibility; and