Deck footings in Ontario don't automatically need rebar: Part 9 of the 2024 Ontario Building Code requires deck footings and piers to carry their loads but doesn't prescribe reinforcement for small residential piers. In practice, many deck drawings and municipal deck guides do show a few vertical bars in each pier, tied into the footing pad, and once your approved drawings show them, they're required. Whether bars make sense depends on the footing type, the height and size of the deck, and whether it's attached to the house or carries a roof or hot tub.
This post covers the deck-specific side of the question: which deck footing types get rebar, the frost-depth rules that decide what kind of footing you have, typical bar sizes, and the decks that need a proper design. For how a reinforced pier is laid out inside a round form, see our post on rebar in sonotubes and concrete piers.
What the Ontario Building Code says
Three parts of the 2024 OBC shape deck foundations:
- Piers. Article 9.15.2.3 says pier type foundations must be designed to support the applied loads from the superstructure. It doesn't specify bars.
- Footings. Subsection 9.15.3 covers footing sizes and thickness. Article 9.15.3.8 sets a minimum footing thickness of the greater of 100 mm or the width of the footing's projection beyond the element it supports. That rule is what lets a plain concrete footing work without bars: a thick pad relative to its overhang doesn't bend enough to crack. There's no general requirement for reinforcement in Part 9 footings, as covered in do footings need rebar under the Ontario Building Code.
- Depth. Article 9.12.2.2 sets minimum foundation depths, which often mean going below the depth of frost penetration. More on that below.
So the code's answer for a typical deck is "size the footings and piers for the load and put them deep enough." Rebar comes in through the designer, the deck drawings or the municipality's standard deck details.
Why many deck footings get rebar anyway
Plain concrete is strong in compression and weak in tension. A deck pier spends most of its life in compression, but it also sees tension in a few ways:
- Frost heave on the sides of the pier. Freezing soil can grip a pier and lift it, while the footing pad at the bottom holds it down. That pulls the pier in tension, and the weak spot is the joint between pier and pad. Vertical bars with a bent leg into the pad tie them together.
- Sideways load on tall posts. A deck several metres off the ground, especially one with a privacy screen or a post-mounted railing, pushes sideways on the top of each pier.
- Uplift at the anchor. Wind on a deck roof or pergola tries to pull posts out of their piers.
- Cold joints. When the pad and the pier are poured at different times, bars across the joint hold them together.
None of that is unusual on a typical attached Ontario deck, which is why designers often show bars even where the code doesn't ask for them.
Which deck footing types get rebar
| Footing type | How it works | Rebar? |
|---|---|---|
| Poured pier on a pad (sonotube on a footing) | A round concrete pier on a wider concrete pad, below frost depth | Commonly shown on drawings: vertical bars with an L-leg into the pad, sometimes ties |
| Flared or bell-shaped footing form | A plastic form that makes a wide base and a pier in one pour | Often shown: vertical bars down into the flared base |
| Plain concrete pad under a post base | A thick pad, poured in place, with the post base bolted on top | Sometimes plain; a thin or wide pad may be reinforced if designed that way |
| Helical piles or ground screws | Steel shafts screwed into the ground, capacity from the manufacturer's design | No rebar; the pile itself is steel |
| Precast deck blocks | Concrete blocks set on grade for floating decks | No rebar |
The first two are what most people mean by "deck footings," and they're where the rebar question comes up.
Frost depth decides the footing
Under Sentence 9.12.2.2.(1), deck foundations follow the minimum depths in Table 9.12.2.2. For a foundation with no heated space, clay and silt soils, and poorly drained coarse soils, generally need to go below the depth of frost penetration (with a 1.2 m minimum in clay). That's why attached decks usually sit on deep poured piers.
Sentence 9.12.2.2.(7) exempts decks and other accessible exterior platforms from those depths when they are:
- not more than 1 storey,
- not more than 55 m² in area,
- not more than 600 mm from finished ground to the underside of the joists,
- not supporting a roof, and
- not attached to another structure, unless it can be shown that differential movement won't harm that structure.
A deck that meets all five can sit on shallow footings or deck blocks, and the rebar question mostly disappears. Most decks attached to a house, or standing higher than 600 mm, don't qualify, and those are the ones that end up on reinforced piers. Your building department confirms what applies to your site.
What size rebar for deck footings?
The drawings set the bar size, number, length and cover. As a guide to what you'll see on residential deck details:
- Vertical bars: commonly 10M or 15M, a small group spaced evenly around the inside of the pier, running from the pad to just below the top.
- Bent leg: an L-shaped bottom on each vertical, sitting in the pad, so the pier and pad act together.
- Ties: closed hoops around the verticals at the spacing on the drawing, on some details.
- Cover: where concrete is cast directly against the soil, as the bottom of a footing usually is, CSA A23.1 calls for at least 75 mm. Our guide to concrete cover for rebar covers the other exposure cases.
For reference, a 10M bar is 11.3 mm in diameter and a 15M bar is 16.0 mm. US deck guides talk about #4 or #5 bars; our post on Canadian vs US rebar sizes explains how those compare. Don't swap sizes or count without checking with the designer, especially if the municipality approved the drawings.
Decks that need a design
Some decks go beyond what a standard deck guide covers, and the footings, piers and rebar are designed for the specific case:
- Decks carrying a roof, a sunroom or a pergola with real wind and snow load.
- Hot tubs and heavy planters. A filled hot tub is a large concentrated load, often on its own pad or framing.
- Tall decks off a second storey or walkout, where lateral support and bracing govern.
- Decks on steel beams and posts, where fewer, more heavily loaded footings carry the deck. Our post on steel beams and posts for decks covers the code limits for deck columns.
- Poor soil, fill, or a high water table.
If your deck is any of these, expect the drawings to show specific footing sizes and rebar, and expect the inspector to check the footing before the pour.
Ordering rebar for deck piers
A set of deck piers usually needs a short, repetitive bar list: the same L-shaped verticals and ties repeated for each pier. Having them cut and bent in the shop means consistent bent legs and hoops, and tagging per pier keeps the site simple.
We cut and bend rebar from 10M to 55M, including L-bars, ties, dowels and custom shapes, tagged and bundled to your bar list, and we deliver across the GTA and Ontario. Send us your deck drawings or bar list for a quote, or see our rebar products. If the posts on those piers are steel, see lally columns in garages, decks and crawl spaces for what works outdoors.
Frequently asked questions
Is rebar required in deck footings in Ontario?
Part 9 of the 2024 Ontario Building Code doesn't prescribe rebar for small deck footings or piers. It requires footings and piers sized and built to carry their loads. Many deck drawings and municipal deck guides show rebar anyway, and when your approved drawings show it, it's required for your job.
What size rebar is used in deck footings?
Your drawings set it. Residential deck pier details commonly show a few 10M or 15M vertical bars with a bent leg into the footing pad. A 10M bar is 11.3 mm in diameter, between a US #3 and #4 bar.
Do deck footings have to go below the frost line in Ontario?
Usually, yes. Deck foundations follow the minimum depths in Table 9.12.2.2, which often mean going below frost penetration. Sentence 9.12.2.2.(7) exempts small, low, freestanding decks that don't support a roof, which can then sit on shallower footings.
Do deck blocks need rebar?
No. Precast deck blocks sit on the ground or on a gravel base and carry the post by bearing only. They are used for floating decks that qualify for the foundation depth exemption, and they don't get reinforcement.
How much concrete cover does rebar need in a deck footing?
Where concrete is cast directly against the soil, as the bottom of a footing usually is, CSA A23.1 calls for at least 75 mm of cover. Your drawings may call for more.
