Wall type 4.1 – Double leaf frames with absorbent material

Double leaf frames with absorbent material (see Diagram 2.37) – minimum distance between inside lining faces of 200 mm; plywood sheathing may be used in the cavity as necessary for structural reasons; each lining to be two or more layers of plasterboard, each sheet of minimum mass per unit area 10 kg/m2, with staggered joints; absorbent material to be unfaced mineral wool batts or quilt (which may be wire reinforced), minimum density 10 kg/m3; minimum thickness of absorbent material – (a) 25 mm if suspended in the cavity between frames; (b) 50 mm if fixed to one frame; or (c) 25 mm per batt (or quilt) if one is fixed to each frame. Note – A masonry core may be used where required for structural purposes, but the core should be connected to only one frame.