Rebar Code Requirements in Ontario: CSA A23 and OBC

Rebar code requirements in Ontario come from the 2024 Ontario Building Code (O. Reg. 163/24), which took effect January 1, 2025, and the CSA standards it references: CSA A23.3 for structural design, CSA A23.1 for concrete materials and construction (including cover), and CSA G30.18 for the steel bar itself. For houses and small buildings, Part 9 of the code adds a handful of prescriptive rules. Everything else is engineered, and the numbers that govern your job are on the structural drawings.

How the Ontario code and CSA standards fit together

The 2024 OBC adopts the National Building Code of Canada 2020 with Ontario amendments. It does not try to describe reinforced concrete design itself. Instead it references CSA standards, which then carry legal weight for the work they cover.

Two things to notice. First, the code references specific editions, and they are not always the newest ones on CSA's shelf. A23.1 and A23.3 have 2024 editions, and G30.18 has been updated since 2009. Your project specification may call for a newer edition, and the engineer decides how to handle any differences. Second, fibre-reinforced polymer standards (CSA S806 and S807) are not referenced at all, which matters if you are considering GFRP. Our post on fiberglass rebar and code compliance covers that route.

Outside the building code, bridges are designed to CSA S6, and Ontario highway work follows MTO's OPSS specifications. Industry practice for detailing, bar supports and placing is set out in the Reinforcing Steel Institute of Canada (RSIC) Manual of Standard Practice, which specifications often reference.

What each CSA standard covers

CSA G30.18: the bar. This is the product standard. It sets the metric sizes from 10M to 55M, the grades, and the rolled-in markings that identify mill, size and grade. Grade 400W, with a 400 MPa minimum yield strength and weldable chemistry, is the everyday bar on Canadian jobs. Our rebar products page has a full size chart with dimensions and weights.

CSA A23.1: building it. A23.1 covers concrete materials and construction. For reinforcement, the parts contractors meet most are the exposure classes (N, F, C, S, A and R), the specified cover in Table 17, minimum clear spacing between bars, bar supports and placing tolerances. The cover values are explained in our concrete cover guide.

CSA A23.3: designing it. A23.3 is the engineer's standard. It sets how much steel a member needs, minimum reinforcement in slabs and walls, maximum bar spacing, development lengths, hooks, lap splices, and the extra detailing required for seismic resistance. Lap splices are the part most often asked about on site, and our lap splice chart shows how A23.3 lengths are worked out.

What Part 9 requires for houses

Part 9 covers houses and small buildings. Its concrete rules are lighter than many people expect, and it sends most reinforced concrete to engineered design. The provisions contractors ask about most:

• Concrete quality (Article 9.3.1.1). Plain and nominally reinforced concrete follows the residential "R" class requirements of CSA A23.1. Other reinforced concrete is designed under Part 4, except for the ICF wall and cold room slab provisions in Part 9.
• Flat ICF walls (Article 9.3.1.1). For flat insulating concrete form walls of up to 2 storeys with floor-to-floor heights of 3 m or less, reinforcement must be CSA G30.18 bar with a minimum 400 MPa yield strength, lapped at least 450 mm for 10M and 650 mm for 15M, and the concrete limited to 19 mm maximum aggregate.
• ICF foundation walls (Article 9.15.4.5). Horizontal and vertical bars go in the inside half of the wall with at least 30 mm of cover from the inside face, with vertical reinforcement taken from tables based on wall thickness. Cold joints need 15M dowels at no more than 600 mm centres, embedded at least 300 mm each side. Our foundation wall rebar guide goes through these walls in detail.
• Reinforced slabs over cold rooms (Section 9.40). This Ontario-specific section covers small slabs suspended over basement cold rooms. It calls for a slab at least 125 mm thick reinforced with 10M bars at no more than 200 mm centres each way, with 30 mm clear cover from the bottom, using Grade 400 bar to CSA G30.18. Slabs outside the section's limits are engineered.
• Footings (Section 9.15.3). Part 9 sizes footings by width and thickness but does not require reinforcement in ordinary footings. Many designs add it anyway, especially over poor soil or for stepped footings. The footing drawings tell you whether bar is required and where.
• Floors on ground (Section 9.16). Slabs on ground must be at least 75 mm thick, and Part 9 does not require reinforcement in them. Floors that support loads from the structure above are designed under Part 4.

That is why searches for a "rebar code for slabs" or "rebar spacing requirements for concrete slabs" rarely find a single answer: for most slabs, there is no prescriptive code spacing. The designer sets it within A23.3's limits, as explained in our slab rebar spacing guide.

Engineered buildings: what the drawings carry

For anything designed under Part 4, including commercial buildings, multi-unit residential, parking structures and anything outside Part 9's scope, the structural engineer applies CSA A23.3 and A23.1 and puts the results on the drawings. A complete set of structural drawings normally gives you:

• concrete strength and exposure class for each element,
• bar sizes, spacing and grade,
• specified cover for each face or element type,
• lap splice lengths, or a lap table in the general notes,
• hook and bend details, and
• any special reinforcement, such as epoxy-coated, stainless or GFRP bar.

If any of those are missing, ask before ordering. A rebar detailer turns the drawings into placing drawings and bar lists, and an experienced detailer will flag gaps in the engineer's information rather than guess.

Who is responsible for what

Code compliance for reinforced concrete is shared:

• The designer or engineer sets the reinforcement and is responsible for the design meeting the code. Part 9 houses follow the code's prescriptive rules through the permit drawings, and anything engineered needs a professional engineer's design.
• The building department reviews the permit drawings and inspects. Footing and foundation inspections typically happen before concrete is placed, so the rebar has to be in and correct at that point.
• The contractor builds to the drawings: right bar, right spacing, right cover, right laps.
• The fabricator supplies bar to the specified grade and standard, cut and bent to the bar list.

Changes on site, such as substituting bar sizes, moving laps, or swapping steel for GFRP, go back to the engineer for approval.

Reading the code yourself

If you want to check a requirement directly, O. Reg. 163/24 is available on Ontario's e-Laws site, but it mainly adopts the National Building Code with amendments. The consolidated text that most builders work from is the Building Code Compendium, published through Publications Ontario. CSA standards are sold by CSA Group, and many municipal building departments will answer questions about how Part 9 applies to a specific project.

Getting the reinforcement right

The code tells you who decides and which standards apply; the drawings tell you the numbers. When you have them, we can prepare bar lists and placing drawings, then cut, bend and tag the bar to match. Send us your drawings for a take-off and quote, or see the rebar products we supply.