(1) Thickness of walls.-Empirically constructed walls of solid, cellular or hollow concrete blocks or of hollow clay blocks shall-

a) subject to the provisions of subsections (2), (3), (4), (6) and (7), have a thickness not less than that prescribed for brick walls in sections 44 to 56; and

b) comply with the requirements of subsection (2) to (7).

(2) Where a brick bearing-wall is required to be not less than 100 millimetres in thickness, a block bearing-wall shall be not less than 150 millimetres in thickness, and such walls 150 millimetres in thickness shall be constructed of blocks with a compressive strength at 28 days of not less than 4,9 megapascals, laid in class B mortar, or better:

Provided that walls of a lesser thickness may be at least 215 millimetres in thickness may be permitted, subject to the prior written approval of the local authority

(3) Where a brick bearing-wall is required to be at least 215 millimetres in thickness, a block bearing-wall shall be at least 200 millimetres in thickness:

Provided that walls of a lesser thickness may be permitted, subject to the prior written approval of the local authority.

(4)The dimensions of panel-walls and of sections of curtain walls between parallel lines of anchors shall be as follows-

a) for light-mass construction, as set out on Figure 2;

b) for construction other than light-mass construction, as for brick construction.

(5) The dimensions of free-standing walls, retaining-walls, parapet-walls and balustrade-walls of blocks shall be not less than the dimensions of such walls of bricks, and all blocks used in such walls shall have a density of not less than 1 400 kilograms per cubic metre.

(6) A block wall which is to support a heavy veneer shall be not less that 200 millimetres in thickness, whether it be bearing or non bearing

(7) If, a two-storey building, an internal wall supporting a flat, heavy roof is higher than 3,3 metres in either the upper storey ot the lower storey, the internal wall in the lower storey shall be-

a) at least 300 millimetres in thickness; or

b) at least 200 millimetres in thickness and constructed of blocks with a compressive strength of at least 4,9 megapascals, laid in class B mortar, or better.

(8) Height of walls.- The maximum height of empirically constructed walls of blocks shall comply with the requirements for walls set out in sections 44 to 46:

Provided that –

a) a bearing-wall shall not exceed three storeys or 12 metres in height, whichever is the lesser; and

b) a curtain-wall shall not exceed a total height of 15 metres, including a gable; and

c) cavity bearing-walls of hollow blocks shall be used in single-storey dwelling-houses.