The general limitation of wall thickness given for stability is that solid walls of brick or block should be at least as thick as one-sixteenth of the storey height. This is a limiting slenderness ratio relating thickness of wall to height, measured between floors and floor and roof that provide lateral support and give stability up the height of the wall. The minimum thickness of external, compartment and separating walls is given in a table in Approved Document A, relating thickness to height and length of wall as illustrated in Fig. 66. Compartment walls are those that are formed to limit the spread of fire and separating walls (party walls) those that separate adjoining buildings, such as the walls between terraced houses.
Cavity walls should have leaves at least 90 mm thick, cavity at least 50 mm wide and the combined thickness of the two leaves plus 20 mm, should be at least the thickness required for a solid wall of the same height and length.
Internal Ioadbearing walls, except compartment and separating walls, should be half the thickness of external walls illustrated in Fig. 66, minus 5 mm, except for the wall in the lowest storey of a three storey building which should be of the same thickness, or 140 mm, whichever is the greater.
Fig. 66 Minimum thickness of walls.