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
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(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
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(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.
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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
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