(1) Masonry walls shall be laterally supported by floor or roof construction or by intersecting masonry walls or buttresses.
(2) The spacing of supports required in Sentence (1) shall be not more than,
(a) 20 times the wall thickness for all loadbearing walls and exterior non-loadbearing walls, and
(b) 36 times the wall thickness for interior non-loadbearing walls.
(3) In applying Sentence (2), the thickness of cavity walls shall be taken as the greater of,
(a) two-thirds of the sum of the thicknesses of the wythes, or
(b) the thickness of the thicker wythe.
(4) Floor and roof structural elements providing lateral support for walls as required in Sentence (1) shall be constructed to transfer lateral loads to walls or buttresses approximately at right angles to the laterally supported walls.