(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, 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 =the sum of the supported joist spans on each storey whose load is transferred to the footing, and
storeys =number of storeys supported by the footing.
(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.