Diagram 4C.14: Sizes of openings and recesses in masonry walls

centre line of buttressing wall or pier; corner of two external walls; inner face of return wall should not be greater than 2.1 m; opening recess recess opening; H; L = length of wall; W1 P2 W2 P3 W3 P4 W4 P5 P1 Notes: Requirements (refer to Table 4C.9 for values of factor X) 1 W1 + W2 + W3 should not exceed 2L divided by 3. 2 W1, W2, W3 or W4 should not exceed 3 m. 3 P1 should be greater than or equal to W1 divided by X. 4 P2 should be greater than or equal to [W1 + W2] divided by X. 5 P3 should be greater than or equal to [W2 + W3] divided by X. 6 P4 should be greater than or equal to W3 divided by X. 7 P5 should be greater than or equal to W4 divided by X but should be not less than 385 mm. In this case the height H of the opening should not exceed 2.1 m. 8 The value of the factor X should be taken from Table 4.9 or it can be given the value 6, provided the compressive strength of the bricks or blocks (in the case of a cavity wall – in the loaded leaf) is not less than 7 N/mm2.