Rebar spacing in a concrete wall is set one of two ways in Ontario: from the prescriptive tables in Part 9 of the 2024 Ontario Building Code, or by a designer working to CSA A23.3. Under Part 9, above-grade flat ICF walls get 10M vertical bars at no more than 400 mm and 10M horizontal bars at no more than 600 mm, while ICF foundation walls take their vertical spacing from tables. For designed walls, CSA A23.3-19 caps bar spacing at three times the wall thickness or 500 mm, whichever is less, and sets minimum amounts of vertical and horizontal steel.
Our guide to foundation wall rebar in Ontario covers the basement wall tables in detail. This post covers spacing and placement across wall types, including above-grade ICF walls and engineered walls.
Two routes: Part 9 tables or a design
Which rules apply depends on the wall:
| Wall | Where spacing comes from |
|---|---|
| Plain poured foundation wall within Table 9.15.4.2.-A | No rebar required under Part 9 |
| Reinforced concrete block foundation wall | OBC Table 9.15.4.2.-B and Sentences 9.15.4.2.(4) to (7) |
| Flat ICF foundation wall | OBC Article 9.15.4.5 and Tables 9.15.4.5.-A to -C |
| Above-grade flat ICF wall | OBC Subsection 9.20.17 |
| Retaining walls, tall walls, walls with surcharge, commercial walls | Engineered design to CSA A23.3 |
The Part 9 ICF rules only apply within set limits. Sentence 9.3.1.1.(4) covers flat ICF walls not exceeding 2 storeys in building height, with a maximum floor-to-floor height of 3 m, in buildings of light-frame construction. Anything outside the Part 9 limits is designed under Part 4, and the drawings govern.
Part 9 spacing at a glance
Here are the prescriptive spacing rules for reinforced walls under the 2024 OBC (O. Reg. 163/24, Division B):
| Wall type | Horizontal bars | Vertical bars | Bar position |
|---|---|---|---|
| ICF foundation wall (9.15.4.5) | 10M within 300 mm of the top, plus 10M at not more than 600 mm o.c. | From Tables 9.15.4.5.-A to -C, from none required up to 10M or 15M at 250 to 400 mm o.c. | Inside half of the wall, at least 30 mm cover from the inside face |
| Above-grade ICF wall (9.20.17.2) | 10M within 300 mm of the top, plus 10M at not more than 600 mm o.c. | 10M at not more than 400 mm o.c. | Middle third of the wall section |
| Reinforced block foundation wall (9.15.4.2) | Bond beams with at least one 15M bar at set locations, plus joint reinforcement in every second course | From Table 9.15.4.2.-B | Vertical bars on the wall centre line |
A few related rules that affect spacing on site:
- Above-grade ICF walls must be at least 140 mm of concrete thick and constant in thickness for the full height (9.20.17.1).
- Openings. In ICF walls, vertical bars interrupted by an opening are placed within 600 mm of each side of it (9.15.4.5 for foundation walls, 9.20.17.2.(3) above grade). Openings in non-loadbearing above-grade ICF walls between 600 mm and 3,000 mm wide get one 10M bar top and bottom, and wider openings get two 10M bars on all four sides, each extending 600 mm past the opening (9.20.17.3). Loadbearing walls need lintels over openings wider than 900 mm (9.20.17.4).
- Laps. For Part 9 ICF walls, bars are lapped at least 450 mm for 10M and 650 mm for 15M (9.3.1.1.(4)).
The foundation wall tables, including the vertical bar spacing for 150, 190 and 240 mm ICF walls at different backfill heights, are set out in our foundation wall rebar guide.
Engineered walls: CSA A23.3 minimum steel and spacing
When a wall is designed, the engineer sizes the bars for the loads: soil pressure, wind, the floors and roof above, and seismic forces where they apply. Underneath the design, CSA A23.3-19 Clause 14.1.8 sets general minimums for walls:
| Requirement | CSA A23.3-19 |
|---|---|
| Maximum bar diameter | One tenth of the wall thickness (14.1.8.2) |
| Two layers required | Walls thicker than 210 mm (14.1.8.3) |
| Maximum spacing, vertical and horizontal | The lesser of 3 times the wall thickness or 500 mm (14.1.8.4) |
| Minimum vertical steel | 0.0015 times the gross area (14.1.8.5) |
| Minimum horizontal steel | 0.002 times the gross area (14.1.8.6) |
These are floors, not targets. Loads often need more, and shear walls and walls in seismic force resisting systems have additional requirements. What the minimums do explain is why a thicker wall gets more steel even when the loads are light: the minimum is tied to the concrete area.
Example: a 200 mm wall. Per metre of wall length, the gross area is 200,000 mm².
- Minimum vertical steel: 0.0015 x 200,000 = 300 mm² per metre. 10M bars (100 mm² each) at 333 mm would just meet it, so a designer might use 10M at 300 mm.
- Minimum horizontal steel: 0.002 x 200,000 = 400 mm² per metre, which is 10M at 250 mm or 15M at 500 mm.
- At 200 mm thick, a single layer is permitted.
Example: a 250 mm wall. Gross area is 250,000 mm² per metre, and because it's thicker than 210 mm it needs two layers.
- Minimum vertical steel: 375 mm² per metre in total. 10M at 500 mm on each face gives 400 mm².
- Minimum horizontal steel: 500 mm² per metre in total. 10M at 400 mm on each face gives 500 mm².
- Spacing can't exceed 500 mm, since three times the thickness (750 mm) is larger.
These examples only show how the minimums work. Real wall designs are usually governed by the loads, and the bar sizes and spacing on your drawings are the ones to build. Our post on maximum rebar spacing under CSA A23.3 covers spacing limits in slabs and beams as well.
Placement: which face, which bar outside
Spacing is half of it. Where the bars sit in the wall matters just as much:
- Single layer. Part 9 puts ICF foundation wall steel in the inside half of the wall (the tension side when soil pushes in), and above-grade ICF steel in the middle third. An engineered single-layer wall shows its position on the section.
- Two layers (EF, each face). Drawings label bars by face, often IF and OF (inside face, outside face) or EF for each face. The two faces don't always get the same bars; a retaining wall usually has heavier steel on the soil side.
- Which direction is outermost. In a two-way layer, either the vertical or horizontal bars sit closer to the form. The section or the general notes should say which; if they don't, ask before the wall is tied, because it changes the cover and the effective depth the designer assumed.
- Cover. CSA A23.1 sets the minimum concrete cover by exposure, and concrete cast against earth needs more than concrete cast against forms. See our concrete cover guide.
- Dowels from the footing. Vertical bars usually lap with dowels set in the footing. Their spacing matches the wall verticals, and their length comes from the lap and embedment on the drawings. See rebar for footings in Ontario.
- Corners and intersections. Horizontal bars need corner bars or bent bars to carry through the corner, typically lapped with the straight bars on each side.
Stem walls and short walls
A stem wall is a short foundation wall between a footing and a slab or floor, common under garages, additions and slab-on-grade buildings. Under Part 9 it's a foundation wall like any other: a plain poured stem wall can be unreinforced within Table 9.15.4.2.-A, and an ICF stem wall follows Article 9.15.4.5. Many stem walls on drawings do carry steel anyway, typically a few horizontal bars and verticals doweled to the footing, because the designer wants to bridge soft spots or tie the wall to the slab. As with any wall, the drawings set the spacing.
Ordering wall steel
Wall reinforcement is mostly straight bars, but the bent pieces are where mistakes happen: corner bars, dowels, U-bars at wall ends and bars around openings. A bar list that lists every piece by mark, size, length and shape, and bundles tagged by wall, saves the crew from cutting and sorting on site. Our post on how to order cut and bend rebar explains how that works.
Getting your wall steel detailed and cut
We prepare bar lists from structural drawings and cut and bend wall steel, including verticals, horizontals, corner bars and footing dowels, tagged by wall. Questions about how your wall should be reinforced belong with your designer or engineer; we build to the drawings.
Send us your foundation or wall drawings for a quote and free take-off, or see our rebar products.
Frequently asked questions
What is the vertical rebar spacing in an ICF wall?
For above-grade flat ICF walls under Part 9 of the 2024 Ontario Building Code, vertical bars are 10M at not more than 400 mm o.c. (Sentence 9.20.17.2.(2)). For ICF foundation walls, vertical spacing comes from Tables 9.15.4.5.-A to -C and depends on wall thickness, height and backfill.
What is the horizontal rebar spacing in a concrete wall?
For Part 9 flat ICF walls it is 10M at not more than 600 mm o.c. plus one 10M bar within 300 mm of the top. For engineered walls, the designer sets it, and CSA A23.3-19 requires at least 0.002 times the gross wall area in horizontal steel, with bars no farther apart than three times the wall thickness or 500 mm.
What is the minimum rebar in a concrete wall?
Under CSA A23.3-19 Clause 14.1.8, a designed wall needs vertical steel of at least 0.0015 and horizontal steel of at least 0.002 times the gross concrete area. A plain poured foundation wall within the limits of OBC Table 9.15.4.2.-A needs no reinforcement at all.
When does a concrete wall need two layers of rebar?
CSA A23.3-19 requires two layers of reinforcement, one near each face, in walls thicker than 210 mm. Thinner walls can have a single layer unless the design calls for two.
