Frost Depth and Footing Depth in Canada

Canada

What Canadian codes actually require for footing depth, and the deck and fence post depths cities publish, each with its source.

The short answer

No Canadian code gives a frost depth for your city. The National Building Code 2020 and every provincial code we checked (Ontario, BC, Alberta, Quebec) leave it to "local experience" (Article 1.1.3.2) and set a 1.2 m (4 ft) minimum for unheated footings on clay or undefined soil, deeper where frost goes deeper (Table 9.12.2.2). Ask your building department for the local figure.

The code rule: Table 9.12.2.2

Minimum depth of foundations below finished ground, from NBC 2020. The NBC 2023 Alberta Edition, BC Building Code 2024 and Quebec's code use the same table. Decks and fence posts fall under "no heated space".

Minimum depths of foundations, NBC 2020 Table 9.12.2.2
Soil Heated space, good drainage Heated space, poor drainage No heated space, good drainage No heated space, poor drainage
Rock No limit No limit No limit No limit
Coarse grained soils No limit No limit No limit Below the depth of frost penetration
Silt No limit No limit Below the depth of frost penetration Below the depth of frost penetration
Clay or soils not clearly defined 1.2 m 1.2 m 1.2 m but not less than the depth of frost penetration 1.2 m but not less than the depth of frost penetration

Good drainage means good soil drainage to at least the depth of frost penetration. Sentence 9.12.2.2.(5) allows shallower foundations where local experience or a design shows they are satisfactory.

When a deck is exempt

NBC 2020 Sentence 9.12.2.2.(7): the table does not apply to decks that are all of these:

  • Not more than 1 storey
  • Not more than 55 m² (592 sq ft)
  • Not more than 600 mm (23 5/8 in) from finished ground to the underside of the joists
  • Not supporting a roof
  • Not attached to another structure, unless differential movement will not harm it

Such decks on surface footings (other than on rock or well drained coarse soil) need a way to reach the footings for re-levelling: a 600 mm by 600 mm crawl space or decking that lifts off easily (9.12.2.2.(8)).

Depths Canadian cities publish

Read in each building department's own document. Check what each one applies to.

Deck and fence footing depths published by Canadian municipalities
Place Depth Applies to Source
Calgary, AB 1.2 m (4 ft) minimum Deck foundations; shallower needs an engineer's design review City of Calgary, Uncovered Deck permit checklist (Aug. 2026)
Edmonton, AB 1.2 m (4 ft) typical Uncovered decks; "dependent on soil conditions" City of Edmonton, Uncovered Deck Design Guide (Dec. 2022)
Winnipeg, MB 1.8 m (6 ft) Decks with joists more than 1 300 mm above ground: "the depth of frost penetration" City of Winnipeg, Decks brochure (Oct. 2025)
Manitoba (province guide) 1.8 m (6 ft) Decks over 1 300 mm high or attached to a structure Manitoba ITS Guide 06, Part 9 Decks (March 2026)
Ottawa, ON 5 ft (1.5 m) Shown on the City's sample sundeck plan (a sample, not a stated rule) City of Ottawa, sundeck application checklist (2014)
Halifax, NS 4 ft (1.2 m) minimum Deck footings for frost protection Halifax Regional Municipality, Decks FAQ (Sept. 2023)
Richmond Hill, ON Below the frost line or 1.2 m, whichever is greater Fence posts Fence By-law, Municipal Code Ch. 973, s. 973.3.31
Carleton Place, ON 1.2 m minimum, unless on sound bedrock Non-floating deck foundations Town of Carleton Place, Part 9 Decks guideline (April 2025)
Port Hope, ON 48 in (1.2 m) Decks attached to a dwelling or needing a guard Municipality of Port Hope, Deck Design Guide (Jan. 2021)
Pickering, ON 1 200 mm Deck foundations, including at the bottom of stair stringers City of Pickering, Deck Construction Guide (May 2025)
Kelowna, BC 600 mm "Depth of frost penetration" in the building bylaw's climatic data; the code's 1.2 m clay minimum can still apply City of Kelowna Building Bylaw No. 7245, s. 8.1

Toronto, Regina, Saskatoon, Montreal, Quebec City and Vancouver do not publish a deck footing depth that we could find. Their permit guides ask you to show the depth on your drawings, so ask the building department.

Common questions

How deep do deck footings need to be in Ontario?
The Ontario Building Code (Table 9.12.2.2) requires footings without heated space on clay or undefined soil to go 1.2 m (4 ft) but not less than the depth of frost penetration. Many Ontario municipalities publish 1.2 m (48 in) in their deck guides; Ottawa's sample plan shows 5 ft. Small floating decks can be exempt.
What is the frost line in Canada?
No Canadian code publishes one. NBC 2020 Article 1.1.3.2 says the depth of frost penetration "shall be established on the basis of local experience", so the number comes from your municipality. Published figures range from 600 mm in Kelowna to 1.8 m in Winnipeg.
Do I need footings below the frost line for a deck?
Not always. NBC 2020 9.12.2.2.(7) exempts decks that are one storey or less, no more than 55 m², no more than 600 mm from the ground to the underside of the joists, not supporting a roof, and not attached to another structure (unless differential movement is shown not to matter). Attached or high decks need frost protection.
How deep should fence posts be in Canada?
Building codes do not set fence post depth. Some municipalities do: Richmond Hill's fence by-law requires posts below the frost line or at least 1.2 m, whichever is greater. Check your local fence by-law.
How deep are deck footings in Calgary and Edmonton?
Calgary requires deck foundations at least 1.2 m (4 ft) deep, or an engineer's review for anything shallower. Edmonton calls 1.2 m (4 ft) typical, depending on soil.
How deep are deck footings in Winnipeg?
1.8 m (6 ft) where the underside of the joists is more than 1 300 mm (4 ft 3 in) above the ground, per the City of Winnipeg and Manitoba's provincial deck guide.