(1) Except as specified in subsection (2), all building-units in masonry construction shall be laid in horizontal courses with their load-bearing surfaces horizontal.

(2) The exceptions to subsection (1) are-

a) stones in random rubble stone walls;

b) stones in natural stone bearing-walls, in which case the beds of the stones shall be approximately level for a minimum distance of 120 millimetres back from the face of the wall;

c) building-units which are permitted to be built to a pattern not forming horizontal courses:

Provided that, for the purposes of section 17, the portion of the wall formed by such units shall be regarded as either an opening or a recess, depending on whether or not such portion extends to a thickness greater than one third of the thickness of the wall;

d) cases where the local authority is satisfied that the design requires the bedding-planes to be inclined to the horizontal.