Ministry of Municipal Affairs PROPOSED CHANGE TO THE 2012 BUILDING CODE O. REG. 332/12 AS AMENDED CHANGE NUMBER: B-09-15-01 SOURCE: Ontario CODE REFERENCE: Div. B \ 9.15.3.4. DESCRIPTION OF THE PROPOSED AMENDMENT The proposed change clarifies the meaning/use of supported joist spans for exterior walls and interior walls EXISTING 2012 BUILDING CODE PROVISION(S) 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. Table 9.15.3.4. Minimum Footing Sizes Forming Part of Sentence 9.15.3.4.(1) Number of Floors Supported 1 2 3 Column 1 Minimum Width of Strip Footings, mm Supporting Exterior Walls(2) Supporting Interior Walls(3) 250 200 350 350 450 500 2 3 Minimum Footing Area for Columns Spaced 3 m o.c.(1), m2 0.40 0.75 1.0 4 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). (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 Building and Development Branch © Copyright Queen’s Printer for Ontario 2016 Page 1 (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. (See Appendix A.) (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. PROPOSED CODE CHANGE 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. Table 9.15.3.4. Minimum Footing Sizes Forming Part of Sentence 9.15.3.4.(1) Number of Floors Supported 1 2 3 Column 1 Minimum Width of Strip Footings, mm Supporting Exterior Walls(2)(4) Supporting Interior Walls(3)(5) 250 200 350 350 450 500 2 3 Minimum Footing Area for Columns Spaced 3 m o.c.(1), m2 0.40 0.75 1.0 4 Notes to Table 9.15.3.4.: (1) See Sentence 9.15.3.7.(1). (2) See Sentence 9.15.3.5.(1). (3) See Sentence 9.15.3.6.(1). (4) Supported joist span means the span of the members on each storey bearing on the exterior wall. (5) Supported joist span means half the sum of the joist spans on both sides of the interior wall. (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 Building and Development Branch © Copyright Queen’s Printer for Ontario 2016 Page 2 (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. (See Appendix A.) (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. RATIONALE FOR CHANGE Problem/General Background Exterior wall footings are calculated using the span of the joists bearing on the exterior wall. Interior wall footings are calculated using half the span of the members bearing on either side of the interior wall (i.e., tributary area). Prior to the inclusion of the footing calculation formula, Supplementary Guideline SG-10 to the 1997 Building code, as well as Appendix A of the 2012 Code, provided the following: Footing Sizes The footing sizes in Table 9.15.3.4. are based on typical construction consisting of a roof, not more than 3 storeys, and centre bearing walls or beams. For this reason, Sentence (1) stipulates a maximum supported joist span of 4.9 m. It has become common to use flat wood trusses or wood I-joists to span greater distances in floors of small buildings. Where these spans exceed 4.9 m, minimum footing sizes may be based on the following method: (a) Determine for each storey the span of joists that will be supported on a given footing. Sum these lengths (sum1). (b) Determine the product of the number of storeys times 4.9 m (sum 2). (c) Determine the ratio of sum 1 to sum 2. (d) Multiply this ratio by the minimum footing sizes in Table 9.15.3.3. to get the required min. footing size. Example: A 2-storey house is built using wood I-joists spanning 6 m. (a) sum 1 = 6 + 6 = 12 m (b) sum 2 = 4.9 x 2 = 9.8 m (c) ratio sum 1/sum 2 = 12/9.8 = 1.22 (d) required minimum footing size = 1.22 x 350 mm (min. footing size provided in Table 9.15.3.3.) = 427 mm The current requirement in the 2012 Building Code will require the interior footings to be twice as big as those calculated based on the previous method described in Supplementary Guideline SG-10. Building and Development Branch © Copyright Queen’s Printer for Ontario 2016 Page 3 Justification/Explanation A correction is needed to ensure that the adjustments to the prescriptive Part 9 footings are consistent with previous editions of the Building Code. Cost/Benefit Implications None anticipated. Enforcement Implications None anticipated. Who is Affected Designers, building officials. Objective Based Analysis Provision Objective/Functional Statement Division B, 9.15.3.4. (2) [F20-OP2.1, OP2.3] [F22-OP2.3, OP2.4] [F20, F22-OH1.1, OH1.2, OH1.3] [F20, F22-OH4] Applies to floors and elements that support floors. [F20-OS2.1, OS2.3] [F22-OS2.3] [F20, F22-OS3.1] Applies to floors and elements that support floors. OTHER SUPPORTING MATERIALS Building and Development Branch © Copyright Queen’s Printer for Ontario 2016 Page 4
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