Calculating Exterior Wall Footing Width and Thickness for a Single-Story Home with Slab-on-Ground Foundation According to Ontario Building Code

[Muha007]

In a single-story home with a slab-on-ground foundation, measuring 12.2 meters (40 feet) wide and 22.57 meters (74 feet 1/2 inch) long, the concrete foundation walls are 229mm thick, with 2x6 stud exterior walls plus brick veneer. The home has no interior bearing walls, a concrete slab floor, and 40' trusses.

I'm wondering if the concrete foundation walls can be smaller than 229mm thick?

Also when calculating the exterior wall footing width and thickness according to the Ontario Building Code Table 9.15.3.4, the number of floors supported is 1, as there are no additional floors beyond the concrete slab. The minimum width of the exterior wall strip footing is 250mm.

Considering the home is wider than 4.9 meters, according to OBC 9.15.3.4.(2), the following formula applies 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.

So the calculation becomes:
W = w • [∑ sjs / (storeys • 4.9)]
W = 250 •[12/(1•4.9)]
W = 250• [12/4.9]
W = 250 • 2.45
W = 612.24mm plus the adjustment of 65mm for the brick veneer according to 9.15.3.5.1.(a).
Where the Exterior Wall Footing Strip would be 677.24mm X 224.12 [Footing Thickness = (612.24-229)/2 = 224.12mm] with the adjustments for brick veneer.

However, since there are no floor joists used for the flooring, can I consider the minimum width and thickness of the exterior wall strip footing as
250mm plus adjustment for the brick veneer 65mm = 315.00mm X 100mm [ (315-229)/2 =43 * according to 9.15.3.8.(1)(a) Footing Thickness shall not be less than 100mm ].

I'm wondering if taking into consideration the Ontario Building Code, the exterior strip footing could be: 677.24mm X 224.12 [Footing Thickness = (612.24-229)/2 = 224.12mm].

Or, since there are no floor joists used, can the exterior strip footing be 315mm wide and 100mm thick? With brick veneer adjustment.

 

[Muha007]

Any Input would be appreciated.

 

[ICE]

Any Input would be appreciated.

It's Sunday evening.... give it a couple months.

 

[TheCommish]

Please convert measurement to Imperial for US members

 

[tmurray]

You will get better input on Canada issues if you place them in the Canada section.

Generally, minimum wall thickness is 150mm. I've never seen anything under 200mm though.

That section is intended to deal with floor joists over 4.9m. In this case where there are no floor joists, I think the building official would have a hard time justifying any increase. However, it might still be a good idea for the designer ton increase the footing size accordingly, with the knowledge that the code does not really address truss span and this could pose a performance issue for the building.