9.15.3.4.Basic Footing Widths and Areas

(1) Except as provided in Sentences (2) and (3) and in Articles 9.15.3.5. to 9.15.3.7., the minimum footing width or area shall comply with Table 9.15.3.4. (2) Where the supported joist span exceeds 4.9 m in buildings with light wood-frame walls, floors and roofs, strip footing widths shall be determined according to (a) Section 4.2., or (b) the following formula: W = w × [ ∑ sjs / (storeys × 4.9)] where W = minimum footing width, w = minimum width of footings supporting joists not exceeding 4.9 m, as defined by Table 9.15.3.4., ∑ sjs = sum of the supported joist spans on each storey bearing on an exterior wall whose load is transferred to the footing, or sum of half of the supported joist spans on each storey bearing on both sides of an interior wall whose load is transferred to the footing, and storeys = number of storeys supported by the footing. (See Note A-9.15.3.4.(2)) (3) Where a foundation rests on gravel, sand or silt in which the water table level is less than the width of the footings below the bearing surface, (a) the footing width for walls shall be not less than twice the width required by Sentences (1) and (2), and Articles 9.15.3.5. and 9.15.3.6., and (b) the footing area for columns shall be not less than twice the area required by Sentences (1) and (2) and Article 9.15.3.7. Table 9.15.3.4. Minimum Footing Sizes Forming Part of Sentence 9.15.3.4.(1) Minimum Width of Strip Footings, mm Minimum Footing Area for Number of Floors Supported Supporting Exterior Walls(2) Supporting Interior Walls(3) Columns Spaced 3 m o.c.(1), m2 1 250 200 0.40 2 350 350 0.75 3 450 500 1.0 Notes to Table 9.15.3.4.: (1) See Sentence 9.15.3.7.(1). (2) See Sentences 9.15.3.5.(1). (3) See Sentence 9.15.3.6.(1).