Skip to content
BCIN ExamBCIN Exam

Code guide

Ontario Building Code Footings: Size, Thickness and Depth

Footing sizes and depths in the 2024 Ontario Building Code: 250 to 450 mm strip footings, 100 mm minimum thickness, 1.2 m depth in clay, column footings.
exterior strip footing, 1 floor supported
250 mm
exterior strip footing, 1 floor supported
minimum footing thickness
100 mm
minimum footing thickness
minimum depth in clay soils
1.2 m
minimum depth in clay soils
joist span limit for the footing table
4.9 m
joist span limit for the footing table

Last updated

Under the 2024 Ontario Building Code, a strip footing under an exterior wall of a light wood-frame house must be at least 250 mm wide for 1 floor, 350 mm for 2 floors and 450 mm for 3 floors, and at least 100 mm thick (OBC Div. B 9.15.3.4.OBC Div. B 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…, 9.15.3.8.OBC Div. B 9.15.3.8. Footing Thickness(1) Footing thickness shall be not less than the greater of (a) 100 mm, or (b) the width of the projection of the footing beyond the supported element.). How deep it goes depends on the soil: in clay or soils not clearly defined, foundations must be at least 1.2 m below finished ground (OBC Div. B 9.12.2.2.OBC Div. B 9.12.2.2. Minimum Depth of Foundations(1) Except as provided in Sentences (4) to (7), the minimum depth of foundations below finished ground level shall conform to Table 9.12.2.2. (2) Where a foundation is insulated in a manner that will reduce the heat flow to the soil beneath the footings, the foundation depth shall conform to that required for…).

This page covers footings for houses and other Part 9 buildings in Division B. Your building department decides how the code applies to your site, and poor soils, fill or high loads take you out of these simple rules and into engineering design.

Footing rules at a glance

Item Rule in short Where to look
Footings required under walls, columns, piers, fireplaces and chimneys bearing on soil or rock 9.15.3.1.
What footings sit on undisturbed soil, rock or compacted granular fill 9.15.3.2.
Table limits joist spans up to 4.9 m, floor live load up to 2.4 kPa 9.15.3.3.
Minimum width or area Table 9.15.3.4., by number of floors supported 9.15.3.4.(1)
Long joist spans formula or Part 4 design 9.15.3.4.(2)
High water table in gravel, sand or silt double the width or area 9.15.3.4.(3)
Brick veneer on exterior walls add 65 mm per storey of veneer 9.15.3.5.(1)(a)
Masonry exterior walls add 130 mm per storey 9.15.3.5.(1)(b)
Flat ICF exterior walls add 150 mm per storey 9.15.3.5.(1)(c)
Thickness 100 mm, or the projection if greater 9.15.3.8.
Step footings rise not more than 600 mm, run not less than 600 mm 9.15.3.9.
Depth Table 9.12.2.2., by soil, drainage and heating 9.12.2.2.

This is our summary of the articles, not a copy of the code tables. Read the full text before you size a real footing.

When the simple footing rules apply

Section 9.15 covers concrete and masonry foundations, wood foundations and flat insulating concrete form (ICF) walls on stable soil with an allowable bearing pressure of 75 kPa or more (9.15.1.1.OBC Div. B 9.15.1.1. General(1) Except as provided in Articles 9.15.1.2. and 9.15.1.3., this Section applies to (a) concrete or unit masonry foundation walls and concrete footings not subject to surcharge (i) on stable soils with an allowable bearing pressure of 75 kPa or greater, and (ii) for buildings of wood-frame or masonry construction, (b)…). Filled ground, peat and sensitive clay (such as leda clay) need footings designed under Section 4.2.

The width table itself has further limits. It applies only where the supported joists span not more than 4.9 m and the floor live load is not more than 2.4 kPa (9.15.3.3.OBC Div. B 9.15.3.3. Application of Footing Width and Area Requirements(1) Except as provided in Sentence 9.15.3.4.(2), the minimum footing width or area requirements provided in Articles 9.15.3.4. to 9.15.3.7. shall apply to footings, where (a) the footings support (i) foundation walls of masonry, concrete, or flat insulating concrete form walls, (ii) above ground walls of masonry, flat…). Residential floors fall within that load. A floor for heavier uses, such as storage, needs design under Section 4.2.

Strip footing widths

Table 9.15.3.4.OBC Div. B Table 9.15.3.4. Minimum Footing Sizes — Forming Part of Sentence 9.15.3.4.(1)Table 9.15.3.4 — Minimum Footing Sizes — Forming Part of Sentence 9.15.3.4.(1) Forming Part of Sentence 9.15.3.4.(1) Number of Floors Supported | Minimum Width of Strip Footings Supporting Exterior Walls[2], mm | Minimum Width of Strip Footings Supporting Interior Walls[3], mm | Minimum Footing Area for Columns Spaced… is short: three rows for 1, 2 or 3 floors supported, and columns for exterior walls, interior walls and column footings. Read it this way:

  1. Count the floors the footing carries. A bungalow footing supports 1 floor, a two-storey house 2.
  2. Pick the column for exterior or interior walls. Interior bearing walls have their own widths, which are not always narrower (at 3 floors the interior figure is larger).
  3. Add the adjustments. For exterior walls, add 65 mm for each storey of brick veneer, 130 mm for each storey of solid masonry and 150 mm for each storey of flat ICF wall that the foundation supports (9.15.3.5.OBC Div. B 9.15.3.5. Adjustments to Footing Widths for Exterior Walls(1) The strip footing widths for exterior walls shown in Table 9.15.3.4. shall be increased by (a) 65 mm for each storey of masonry veneer over wood-frame construction supported by the foundation wall, (b) 130 mm for each storey of masonry construction supported by the foundation wall, and (c) 150 mm for each storey…). Interior loadbearing masonry walls add 100 mm per masonry storey (9.15.3.6.OBC Div. B 9.15.3.6. Adjustments to Footing Widths for Interior Walls(1) The minimum strip footing widths for interior loadbearing masonry walls shown in Table 9.15.3.4. shall be increased by 100 mm for each storey of masonry construction supported by the footing. (2) Footings for interior non-loadbearing masonry walls shall be not less than 200 mm wide for walls up to 5.5 m high and…).
  4. Check the water table. On gravel, sand or silt where the water table is closer to the bearing surface than the footing width, double the result (9.15.3.4.(3)OBC Div. B 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…).

Our worked example

A two-storey wood-frame house with brick veneer on both storeys, on good soil, joists spanning 4.2 m:

  • Base width for an exterior wall supporting 2 floors: 350 mm.
  • Veneer adjustment: 2 storeys × 65 mm = 130 mm.
  • Minimum exterior footing width: 350 + 130 = 480 mm.

If the joists spanned more than 4.9 m, you would scale the width with the formula in 9.15.3.4.(2)OBC Div. B 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…, which multiplies the table width by the sum of supported joist spans divided by (storeys × 4.9), or design under Section 4.2. The footing sizing method in our Calculation Lab walks through that formula and the column footing adjustment step by step.

Column footings

The table gives a footing area for columns spaced 3 m apart: 0.40 m² for 1 floor, 0.75 m² for 2 floors and 1.0 m² for 3 floors. For any other column spacing, adjust the area in proportion to the distance between columns (9.15.3.7.OBC Div. B 9.15.3.7. Adjustments to Footing Area for Columns(1) The footing area for column spacings other than shown in Table 9.15.3.4. shall be adjusted in proportion to the distance between columns.). As an example, a column carrying 1 floor with columns 2.4 m apart would need 0.40 × 2.4 / 3 = 0.32 m², which is a square pad about 570 mm on a side. Water table doubling applies to columns too.

Thickness and steps

A footing must be at least 100 mm thick and at least as thick as its projection beyond the wall or column (9.15.3.8.OBC Div. B 9.15.3.8. Footing Thickness(1) Footing thickness shall be not less than the greater of (a) 100 mm, or (b) the width of the projection of the footing beyond the supported element.). A 480 mm footing under a 200 mm wall, centred, projects 140 mm each side, so it needs at least 140 mm thickness.

On sloping sites, step footings are allowed. Each vertical step can rise not more than 600 mm, and the horizontal part between steps must be at least 600 mm long (9.15.3.9.OBC Div. B 9.15.3.9. Step Footings(1) Where step footings are used, (a) the vertical rise between horizontal portions shall not exceed 600 mm, and (b) the horizontal distance between risers shall be not less than 600 mm.).

Footing depth and frost

Table 9.12.2.2.OBC Div. B Table 9.12.2.2. Minimum Depths of Foundations — Forming Part of Sentence 9.12.2.2.(1)Table 9.12.2.2 — Minimum Depths of Foundations — Forming Part of Sentence 9.12.2.2.(1) Forming Part of Sentence 9.12.2.2.(1) Type of Soil | Min Depth of Foundation Containing Heated Basement or Crawl Space[1] With Good Soil Drainage | Min Depth of Foundation Containing Heated Basement or Crawl Space[1] With Poor Soil… sets minimum foundation depths by soil type, soil drainage and whether the foundation encloses heated space:

  • Rock: no minimum depth.
  • Coarse-grained soils: no minimum, except an unheated foundation on poorly drained soil goes below the depth of frost penetration.
  • Silt: an unheated foundation goes below the depth of frost penetration.
  • Clay or soils not clearly defined: at least 1.2 m, and for unheated foundations also not less than the depth of frost penetration.

A foundation insulated so that it cuts heat flow to the soil under the footings is treated as "containing no heated space" (9.12.2.2.(2)OBC Div. B 9.12.2.2. Minimum Depth of Foundations(1) Except as provided in Sentences (4) to (7), the minimum depth of foundations below finished ground level shall conform to Table 9.12.2.2. (2) Where a foundation is insulated in a manner that will reduce the heat flow to the soil beneath the footings, the foundation depth shall conform to that required for…). Depths can be reduced where local experience or a design shows lesser depths work (9.12.2.2.(5)OBC Div. B 9.12.2.2. Minimum Depth of Foundations(1) Except as provided in Sentences (4) to (7), the minimum depth of foundations below finished ground level shall conform to Table 9.12.2.2. (2) Where a foundation is insulated in a manner that will reduce the heat flow to the soil beneath the footings, the foundation depth shall conform to that required for…).

The code does not print a frost depth for Ontario. Municipalities and local practice set the expected value, so ask your building department.

Exemptions. Concrete steps with 1 or 2 risers can sit on the ground. Small accessory buildings (not masonry, 1 storey, not more than 55 m², joists not more than 600 mm above ground) and small freestanding decks with the same size and height limits are exempt from the depth table (9.12.2.2.(4), (6) and (7)OBC Div. B 9.12.2.2. Minimum Depth of Foundations(1) Except as provided in Sentences (4) to (7), the minimum depth of foundations below finished ground level shall conform to Table 9.12.2.2. (2) Where a foundation is insulated in a manner that will reduce the heat flow to the soil beneath the footings, the foundation depth shall conform to that required for…). See the deck building code guide for deck piers.

Common mistakes

  1. Forgetting the veneer adjustment. Brick on a wood-frame house widens the exterior footing by 65 mm per storey.
  2. Using the table with long joists. Past 4.9 m of supported span, the plain table no longer applies.
  3. Thin footings with wide projections. Thickness must match the projection, not just the 100 mm minimum.
  4. Assuming one frost depth. Depth depends on soil type, drainage and whether the space is heated.
  5. Footings on fill. Footings rest on undisturbed soil, rock or compacted granular fill (9.15.3.2.OBC Div. B 9.15.3.2. Support of Footings(1) Footings shall rest on undisturbed soil, rock or compacted granular fill. (2) Granular fill shall not contain pyritic material in a concentration that would adversely affect its stability or the performance of assemblies separating dissimilar environments. (See also Article 9.4.4.4. and Note A-9.4.4.4.(1))); other fill needs design.

How to look it up yourself

Open Division B, Part 9 of the 2024 Compendium. Section 9.15 is "Footings and Foundations" and Subsection 9.15.3. holds the footing articles. Search terms that appear in the code text:

  • "Minimum Footing Sizes" (the table title)
  • "Basic Footing Widths and Areas" (9.15.3.4.)
  • "masonry veneer over wood-frame" (the veneer adjustment)
  • "Minimum Depth of Foundations" (9.12.2.2.)
  • "depth of frost penetration" (the depth table)

Read the article in the code viewer alongside the depth article.

BCIN exam angle

Footing width with veneer and column footing area are classic calculation questions on the House and Small Buildings exams. Study the free House chapter on excavation, dampproofing, footings and foundations or the Small Buildings chapter on foundations, framing and structure, then try the free quiz on the House exam or Small Buildings exam page.

Based on the official 2024 Building Code Compendium on ontario.ca.

© King's Printer for Ontario, 2024. Reproduced with permission.

Sources

Free accountNo card needed

Start practising for your BCIN exam, free

  • A free practice quiz for each exam
  • Every answer cites its 2024 OBC article
  • Full 70 question timed simulations with a paid plan
  • Works on phone, tablet and computer
Create a free account

Frequently asked questions

How wide does a footing need to be in Ontario?
For a typical light wood-frame house on good soil, a strip footing under an exterior wall must be at least 250 mm wide when it supports 1 floor, 350 mm for 2 floors and 450 mm for 3 floors. Brick veneer and masonry walls add width per storey (Division B, Articles 9.15.3.4. and 9.15.3.5.).
How thick does a footing have to be?
At least 100 mm, and never less than the distance the footing projects beyond the wall or column it supports (Division B, Article 9.15.3.8.).
How deep do footings have to be in Ontario?
It depends on soil and drainage. In clay or soils that are not clearly defined, foundations must be at least 1.2 m deep, and for unheated structures also not less than the depth of frost penetration. Rock has no minimum, and well-drained coarse soils have no minimum (Division B, Article 9.12.2.2. and Table 9.12.2.2.).
What is the frost depth in Ontario?
The Building Code does not publish one frost depth for the province. It sets the 1.2 m minimum for clay and unclear soils and otherwise refers to the depth of frost penetration, which your municipality or local experience establishes. Ask your building department for the local value.
Do deck footings have to go below frost?
Usually yes, but a deck of not more than 1 storey and 55 m², with joists not more than 600 mm above ground, no roof, and not attached to another structure (unless differential movement is shown not to matter) is exempt from the depth table (Division B, Sentence 9.12.2.2.(7)).