Do I need a permit to build a deck in Ontario?

The Building Code Act, 1992 requires a permit to construct a building (s. 8), and its definition of building includes a structure occupying more than 10 m2 that consists of a floor or a structural system serving that function (s. 1(1)). Division C, Article 1.3.1.1. lists permit exemptions such as small sheds, and decks are not among them. Ask your municipality before you build, since it applies the Act and may have its own guidance.

What load must a deck be designed for?

A deck serving a single dwelling unit must carry the specified roof snow load for the location or 1.9 kPa, whichever is greater (Division B, Sentence 9.4.2.3.(1)).

How deep do deck footings have to be in Ontario?

Generally to the depths in Table 9.12.2.2., which depend on soil type and drainage; for clay or poorly defined soils that is at least 1.2 m and not less than the frost depth. A small freestanding deck can be exempt (Division B, Sentence 9.12.2.2.(7)).

Can a deck sit on deck blocks without frost footings?

The frost depth requirement does not apply to a deck that is not more than 1 storey, not more than 55 m2, has joists not more than 600 mm above finished ground, supports no roof and is not attached to another structure unless differential movement is shown not to harm it (Division B, Sentence 9.12.2.2.(7)).

Where are deck joist spans in the Ontario Building Code?

Wood floor joist spans are in Span Tables 9.23.4.2.-A and -B, and built-up and glulam beam spans in Tables 9.23.4.2.-H to -K (Division B, Article 9.23.4.2.). They apply to residential-level floor loads (Article 9.23.4.1.).

Deck Building Code Ontario: 2024 Footings, Spans and Permits

Last updated October 22, 2026

In the 2024 Ontario Building Code, a deck serving a single house must be designed for the specified roof snow load or 1.9 kPa, whichever is greater (OBC Div. B 9.4.2.3.), and its footings must generally reach the depths in Table 9.12.2.2, unless it qualifies as a small freestanding deck of not more than 55 m² with joists not more than 600 mm above grade (OBC Div. B 9.12.2.2.). Guards, stairs, spans and post anchorage each have their own articles, covered below.

There is no single "deck section" in the code. The rules are spread across Part 9 of Division B, and the permit rules are in the Building Code Act and Division C. This page pulls them together in plain language. Municipal zoning bylaws (setbacks, lot coverage) and permit conditions often add requirements, so confirm with your building department before you dig.

Deck rules at a glance

Topic	Key rule	Article
Design load	greater of roof snow load or 1.9 kPa	9.4.2.3.(1)
Footing depth	per Table 9.12.2.2 (soil and drainage)	9.12.2.2.(1)
Small deck exemption from footing depth	1 storey, 55 m² max, joists 600 mm max above ground, no roof, not attached (one exception)	9.12.2.2.(7)
Posts and columns	Section 9.17 covers up to 2 deck levels, joists bearing up to 5 m	9.17.1.1.(1)(b)
Post anchorage	anchor to resist uplift and lateral movement, small deck exemption	9.23.6.2.
Joist spans	Span Tables 9.23.4.2.-A and -B	9.23.4.2.(1)
Beam spans	Span Tables 9.23.4.2.-H to -K	9.23.4.2.(3)
Beam end bearing	89 mm unless the span table notes say otherwise	9.23.8.1.
Wood near the ground	pressure-treated where clearance is under 150 mm	9.3.2.9.(3)
Guards	over 600 mm drop; 900 mm or 1,070 mm high	9.8.8.1., 9.8.8.3.

This is our own summary. Read each article in full before relying on it.

Loads

9.4.2.3.(1) says balconies, decks and other accessible exterior platforms that serve a single dwelling unit and are exposed to snow must carry the specified roof snow load or 1.9 kPa, whichever is greater. Snow loads come from the formula in 9.4.2.2., using ground snow and rain loads for your location from Supplementary Standard SB-1. In snowy parts of Ontario, the snow load, not the 1.9 kPa minimum, can govern.

Footings and foundations

Depth. 9.12.2.2. sends you to Table 9.12.2.2., which sets minimum depths by soil type and drainage. A deck footing is a foundation "containing no heated space." For clay or soils not clearly defined, that means at least 1.2 m and not less than the depth of frost penetration. Rock has no limit, and neither do coarse-grained soils with good drainage. Silt needs footings below the depth of frost penetration. Lesser depths are allowed where local experience or a design shows they are satisfactory.

The small deck exemption. The depth table does not apply to a deck that is not more than 1 storey, not more than 55 m² in area, has not more than 600 mm from finished ground to the underside of the joists, supports no roof, and is not attached to another structure, unless it can be shown that differential movement will not harm that structure (9.12.2.2.(7)). This is the clause behind low, floating decks.

Size. Footing widths and column footing areas are in 9.15.3.4. and its table, based on the number of floors supported and the column spacing. Ask your building department which values it expects for deck piers.

Posts, beams and joists

Posts. Section 9.17 covers columns supporting beams that carry not more than 2 levels of wood-frame decks (or 1 level plus a roof), where the joists bearing on the beam are not more than 5 m long, the snow plus occupancy load does not exceed 4.8 kPa, and the deck serves a single residential suite (9.17.1.1.). Outside those limits, Part 4 design is required. Columns must be fastened to what they support and braced against racking, except posts not more than 600 mm long under a deck with no superstructure (9.17.2.2.).

Anchorage. Exterior posts generally must be anchored to resist uplift and lateral movement. Where deck posts are on a platform with not more than 600 mm from ground to the underside of the joists, the posts must be anchored to the foundation, or the joists or beams anchored to the ground, to resist uplift and lateral movement. A small, freestanding, roofless, single-storey deck of not more than 55 m² is exempt (9.23.6.2.).

Spans. Joist spans come from Span Tables 9.23.4.2.-A and -B and beam spans from Tables 9.23.4.2.-H to -K (9.23.4.2.). Each table is read by species group, grade, member size and spacing (or, for beams, supported length). The tables apply only to floors carrying residential-level loads (9.23.4.1.), so if the snow load at your site pushes the deck load above that, the tables alone do not answer the question and a design under Part 4 or engineering guidance is needed (9.4.1.1.).

Bearing and connections. Beams need at least 89 mm of end bearing unless the span table notes say otherwise (9.23.8.1.), and joists at least 38 mm (9.23.9.1.). Joists framed into the side of a wood beam sit on joist hangers or ledger strips of the sizes in 9.23.9.2..

Protecting the wood

Structural wood less than 150 mm above finished ground must be pressure-treated with a preservative (9.3.2.9.(3)). The same article sets the CSA O80 use categories: for example UC3.2 for exterior above-ground wood and UC4.1 for ground contact, with treated wood marked to show its category. Where termites are known to occur, extra rules apply.

Guards and stairs

A deck more than 600 mm above the ground within 1.2 m of its edge needs a guard (9.8.8.1.): 900 mm high where the deck is not more than 1,800 mm above finished ground, 1,070 mm above that (9.8.8.3.). Wood guards built to SB-7 are deemed to meet the load requirements (9.8.8.2.). Deck stairs follow the private stair rules in Table 9.8.4.1., and need a handrail once they have more than 3 risers (9.8.7.1.). See deck railing height.

Permits

The Building Code Act, 1992 says no one may construct a building without a permit from the chief building official (BCA s. 8). The Act defines a building to include a structure occupying more than 10 m² that consists of a wall, roof or floor, or a structural system serving that function (BCA s. 1(1)). The exemptions in Div. C 1.3.1.1. cover things like tents and small sheds, not decks. Municipalities apply these rules, and many publish deck permit guides, so check with yours.

Common mistakes

Using the floating deck exemption on an attached deck without showing differential movement will not harm the house.
Picking spans from the wrong table (ceiling or roof joists instead of floor joists).
Forgetting snow load in heavy-snow areas.
Ignoring zoning setbacks, which come from the municipal bylaw, not the Building Code.
Untreated or wrong-category lumber near the ground.

How to look it up yourself

In Division B, Part 9, search the 2024 Compendium for "decks and other accessible exterior platforms" (it appears in 9.4.2.3., 9.12.2.2. and 9.17.1.1.), "Minimum Depth of Foundations", "Anchorage of Columns and Posts" and "Maximum Spans for Floor Joists". For permits, search the Act for "No person shall construct or demolish a building".

Decks pull together structure, foundations and guards, all of which are on the House exam syllabus. Read the free House exam study guide and try the free practice quiz on that page.

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

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Deck Building Code in Ontario