Structure: Approved Document A

O N L I N E V E R S I O N A1/2 THICKNESS OF WALLS IN CERTAIN SMALL BUILDINGS Table 7 N ormalised compressive strength of masonry units of clay and calcium silicate blocks complying with BS EN 771-1 and 2 (N/mm2) Standard Condition (See Diagram 9) Group 1 masonry units Group 2 masonry units Clay masonry units to BS EN 771-1 A 5.0 8.0 Calcium silicate masonry units to BS EN 771-2 B 7.5 11.0 C 15.0 21.0 Notes: 1. Values in this table are normalised compressive strengths (N/mm²). Compressive strengths of masonry units should be derived according to EN 772-1. 2. The table applies to clay and calcium silicate block masonry units where the work size exceeds 337.5mm in length or 112.5mm in height. 3. Group 1 masonry units have not more than 25% formed voids (20% for frogged bricks). Group 2 masonry units have formed voids greater than 25%, but not more than 55%. 2C22 Mortar: Mortar should be: Diagram 10 Maximum span of floors a. one of the following: i. Mortar designation (iii) according to See para 2C23 BS EN 1996-1-1:2005 with its UK National Annex; ii. Strength class M4 according to BS EN 998-2:2010; iii. 1:1:5 to 6 CEM I, lime, and fine aggregate measured by volume of dry materials, or b. of equivalent or greater strength and durability to the specifications in a. above. Loading on walls 2C23 Maximum span of floors: The maximum span for any floor supported by a wall is 6m where the span is measured centre to centre of bearing (see Diagram 10). 2C24 Other loading conditions: a. Vertical loading on walls should be distributed. This may be assumed for concrete floor slabs, precast concrete floors, and timber floors designed in accordance with section 2B, and where the bearing length for lintels is 150mm or greater. Where a lintel has a clear End restraint span of 1200mm or less the bearing length may be reduced to 100mm. 2C25 Vertical lateral restraint to walls b. Differences in level of ground or other solid The ends of every wall should be bonded or construction between one side of the wall otherwise securely tied throughout their full and the other should be less than 4 times the height to a buttressing wall, pier or chimney. thickness of the wall as shown in Diagram 11. Long walls may be provided with intermediate c. The combined dead and imposed load buttressing walls, piers or chimneys dividing should not exceed 70kN/m at base of wall the wall into distinct lengths within each storey; (see Diagram 11). each distinct length is a supported wall for the purposes of this section. The intermediate d. Walls should not be subjected to lateral load buttressing walls, piers or chimneys should other than from wind, and that covered by provide lateral restraint to the full height of the paragraph 2C24(b). supported wall, but they may be staggered at each storey. 2C26 Buttressing walls If the buttressing wall is not itself a supported wall its thickness T2 should not be less than: Continued on page 27 Approved Document A Structure O N L I N E V E R S I O N 25