Table 4E.1: Minimum width of strip foundations

Type No. | Type of subsoil | Condition of subsoil | Field test applicable | Total load of load bearing wall not greater than (kN/m): 20, 30, 40, 50, 60, 70 | Minimum width of strip foundation (mm) 1 | Rock | Not inferior to sandstone, limestone or firm chalk | Requires at least a pneumatic or other mechanically operated pick for excavation | In each case not less than the width of the wall 2 | Gravel or sand | Medium dense | Requires pick for excavation. Wooden peg 50 mm square in cross section hard to drive beyond 150 mm | 250, 300, 400, 500, 600, 650 3 | Clay or sandy clay | Stiff | Can be indented slightly by thumb | 250, 300, 400, 500, 600, 650 4 | Clay or sandy clay | Firm | Thumb makes impression easily | 300, 350, 450, 600, 750, 850 5 | Sand, silty sand or clayey sand | Loose | Can be excavated with a spade. Wooden peg 50 mm square in cross section can be easily driven | 400, 600 | Note: Foundations on subsoil types 5 & 6 do not fall within the provisions of this Section if the total load exceeds 30 kN/m. 6 | Silt, clay or sandy clay & silt | Soft | Finger pushes in up to 10 mm | 450, 650 7 | Silt, clay or sandy clay & silt | Very soft | Finger easily pushes in up to 25 mm | Refer to specialist advice