Whether a foundation wall needs rebar in Ontario depends on what it is built from and how much soil it holds back. Under Part 9 of the 2024 Ontario Building Code, a solid poured concrete wall within the limits of Table 9.15.4.2.-A can be plain concrete. Reinforced concrete block walls follow Table 9.15.4.2.-B, flat ICF walls always carry horizontal bars and usually vertical bars under Article 9.15.4.5, and any wall outside those tables is reinforced to an engineer's design.
The numbers below are taken from the 2024 OBC (O. Reg. 163/24, Division B, Subsection 9.15.4). The 2024 code adopted the National Building Code 2020 numbering, so article and table numbers differ from the 2012 OBC.
Which foundation walls need rebar
Start by identifying the wall type, because each one has its own rule:
| Wall type | Rebar under Part 9? | Where the rule is |
|---|---|---|
| Solid poured concrete | Not required within Table 9.15.4.2.-A limits | 9.15.4.2.(1) |
| Unreinforced concrete block | Not required within Table 9.15.4.2.-A limits | 9.15.4.2.(1) |
| Reinforced concrete block | Vertical bars, bond beams and joint reinforcement | 9.15.4.2.(3) to (7), Table 9.15.4.2.-B |
| Flat ICF | Horizontal and vertical bars | 9.15.4.5, Tables 9.15.4.5.-A to -C |
| Anything outside these limits | Engineered | Part 4 via 9.15.1.1.(2) and 9.4 |
These tables only apply inside Part 9's foundation scope: stable soils with an allowable bearing pressure of 75 kPa or more, no surcharge, and buildings of wood-frame or masonry construction, or ICF buildings of not more than 2 storeys with a floor-to-floor height of 3 m or less (Article 9.15.1.1). Retaining more soil, carrying heavier loads or building on poor ground takes you out of the tables and into design.
Plain poured concrete walls: Table 9.15.4.2.-A
For solid concrete walls up to 3.0 m in unsupported height, Table 9.15.4.2.-A sets a minimum wall thickness for a given height of finished ground above the basement floor. Inside those limits, Part 9 doesn't require any reinforcement.
Here are the poured concrete rows. Values are the maximum height of finished ground above the basement floor (or crawl space ground cover), in metres.
| Concrete strength | Wall thickness | Not laterally supported at top | Supported at top, wall up to 2.5 m | Supported, over 2.5 to 2.75 m | Supported, over 2.75 to 3.0 m |
|---|---|---|---|---|---|
| 15 MPa | 150 mm | 0.8 | 1.5 | 1.5 | 1.4 |
| 15 MPa | 200 mm | 1.2 | 2.15 | 2.15 | 2.1 |
| 15 MPa | 250 mm | 1.4 | 2.3 | 2.6 | 2.5 |
| 15 MPa | 300 mm | 1.5 | 2.3 | 2.6 | 2.85 |
| 20 MPa | 150 mm | 0.8 | 1.8 | 1.6 | 1.6 |
| 20 MPa | 200 mm | 1.2 | 2.3 | 2.3 | 2.2 |
| 20 MPa | 250 mm | 1.4 | 2.3 | 2.6 | 2.85 |
| 20 MPa | 300 mm | 1.5 | 2.3 | 2.6 | 2.85 |
Two things change the picture:
- Lateral support at the top. Article 9.15.4.3 says a wall counts as supported at the top if, for example, the floor joists are embedded in it, the floor system is anchored to it with anchor bolts, or it carries a solid masonry or ICF wall above. A wall without that support can hold back much less soil.
- Openings. Under Sentence 9.15.4.3.(3), the part of the wall below an opening is treated as laterally unsupported if the opening is more than 1.2 m wide, or if openings add up to more than 25% of the wall length, unless the wall around the opening is reinforced to withstand earth pressure. That is a common reason a "plain" basement wall ends up with bars around a wide window or walkout.
Exterior foundation walls must also extend at least 150 mm above finished ground (9.15.4.6), and walls longer than 25 m need crack control joints at intervals of not more than 15 m (9.15.4.9).
Reinforced concrete block walls: Table 9.15.4.2.-B
When backfill gets too high for unreinforced block, Table 9.15.4.2.-B gives the size and spacing of continuous vertical bars for 190 mm and 240 mm block walls that are laterally supported at the top. The table uses 15M, 20M and 25M bars, and the spacing tightens as the backfill height increases. At low backfill heights, such as 0.8 m, it requires no reinforcement at all. At the highest backfill it lists, some wall heights are marked not applicable, meaning the prescriptive option ends and the wall must be designed.
Wherever block walls are required to be reinforced, Sentences 9.15.4.2.(4) to (7) add rules that apply regardless of the table row:
- Continuous vertical bars at corners, wall ends, intersections, changes in wall height, the jambs of every opening and at movement joints.
- Vertical bars running from the top of the footing to the top of the wall, placed along the centre line of the wall.
- A continuous horizontal bond beam with at least one 15M bar along the top of the wall, at the sill and head of openings wider than 1.20 m, and at structurally connected floors.
- Ladder or truss-type joint reinforcement of at least 3.8 mm diameter (No. 9 ASWG) in every second course.
Sentence 9.15.2.2.(3) also requires Type S mortar and coarse grout for these walls.
ICF foundation walls: Article 9.15.4.5
Flat ICF walls are the one wall type where Part 9 always calls for steel. Article 9.15.4.5 requires:
Horizontal bars: one 10M bar not more than 300 mm from the top of the wall, plus 10M bars at not more than 600 mm o.c., placed in the inside half of the wall with at least 30 mm of cover from the inside face of the concrete.
Vertical bars: sized and spaced from Tables 9.15.4.5.-A to -C, also in the inside half of the wall with 30 mm minimum cover from the inside face, and placed within 600 mm of each side of any opening that interrupts them.
The vertical requirement for the thinnest wall is the most demanding:
| 150 mm ICF wall: finished ground above basement floor | Wall height up to 2.44 m | Up to 2.75 m | Up to 3.00 m |
|---|---|---|---|
| 1.35 m | 10M at 400 mm | 10M at 400 mm | 10M at 400 mm |
| 1.60 m | 10M at 400 mm | 10M at 380 mm | 10M at 380 mm |
| 2.00 m | 10M at 380 mm | 10M at 380 mm | 10M at 380 mm |
| 2.20 m | 10M at 250 mm | 10M at 250 mm | 10M at 250 mm |
| 2.35 m | n/a | 10M at 250 mm | 10M at 250 mm |
| 2.60 m | n/a | 10M at 250 mm | 10M at 250 mm |
| 3.00 m | n/a | n/a | 10M at 250 mm |
Thicker walls need less. In a 190 mm wall (Table 9.15.4.5.-B), no vertical bars are required at 2.20 m of backfill on a wall up to 2.44 m high, and the requirement rises to 10M at 300 or 400 mm, then 15M at 400 mm for the tallest walls and highest backfill. In a 240 mm wall (Table 9.15.4.5.-C), none are required up to 2.20 m of backfill, and 15M at 400 mm covers the higher rows.
ICF walls also have rules at the edges:
- Cold joints get at least one 15M bar at not more than 600 mm o.c., embedded at least 300 mm each side (9.15.4.5.(3)).
- Openings are reinforced under Article 9.20.17.3 or 9.20.17.4.
- Footing dowels. One way to provide lateral support at the bottom is dowelling into the footing with 15M at not more than 1.2 m o.c., or 10M at not more than 600 mm o.c. (9.15.4.4). Our post on rebar in footings covers the footing side.
- Material and laps. Sentence 9.3.1.1.(4) requires bars to CSA G30.18 with a minimum specified yield strength of 400 MPa, lapped at least 450 mm for 10M and 650 mm for 15M.
Engineered walls and what "the drawings" means
Most of the reinforced foundation walls we see on drawings are not built from these tables at all. Walls taller than 3.0 m, walls holding back more soil, walls on weak ground, retaining walls, walls with large openings and anything with surcharge (a driveway, an adjacent footing, a slope) are designed by an engineer. The structural drawings then show bar sizes, spacing, laps, dowels, corner bars and cover, and those govern over anything in Part 9.
When you read those drawings, look for:
- Vertical and horizontal bar marks with size and spacing, such as 15M at 400 o.c., and which face of the wall they go on.
- Lap lengths. These come from CSA A23.3 design, not a single number. See our lap splice length chart.
- Concrete cover. Cover against soil is greater than interior cover under CSA A23.1. See concrete cover for rebar.
- Corner and intersection bars, which are bent shapes, plus extra bars around openings.
Estimating how much rebar a basement wall takes
Once the size and spacing are known, quantity is arithmetic. Take a 150 mm ICF wall that needs 10M vertical bars at 400 mm o.c., horizontals at 600 mm plus the top bar, on a 40 m perimeter:
- Verticals: 40 m divided by 0.4 m is 100 bars, plus extras at openings and corners. Each bar is the wall height plus any dowel lap.
- Horizontals: count the rows from the spacing and wall height, multiply by the perimeter, and add one lap for every splice and the corner bars.
- Weight: multiply the total metres of each size by its weight per metre (0.785 kg/m for 10M, 1.570 kg/m for 15M, from our rebar sizes chart).
Openings, steps in the wall and laps add up quickly, which is why a detailed bar list beats a rough take-off.
Get your foundation wall bar list
Send us your foundation drawings and we'll prepare a bar list, cut and bend the verticals, horizontals, corner bars and dowels, and tag every bundle to its wall. See our rebar products for what we supply. Design questions about your wall belong with your designer or engineer; we build to the drawings.
Frequently asked questions
Is rebar required in a poured concrete foundation wall in Ontario?
Not always. Under Part 9 of the 2024 OBC, a solid concrete foundation wall that meets the thickness and backfill limits in Table 9.15.4.2.-A can be plain concrete. Walls outside those limits, and walls an engineer designs, are reinforced to the design.
What is the rebar spacing for an ICF basement wall?
Article 9.15.4.5 requires horizontal 10M bars at not more than 600 mm o.c. plus one 10M bar within 300 mm of the top. Vertical bars depend on wall thickness, wall height and backfill height, from Tables 9.15.4.5.-A to -C, ranging from none required to 10M or 15M at 250 to 400 mm o.c.
What size rebar is used in basement walls?
The prescriptive OBC tables use 10M, 15M, 20M and 25M depending on the wall type. Most house foundation walls that are reinforced use 10M or 15M, but the size on your job comes from the drawings.
How long should rebar laps be in a foundation wall?
For flat ICF walls built to Part 9, Sentence 9.3.1.1.(4) requires laps of at least 450 mm for 10M bars and 650 mm for 15M bars. For engineered walls, lap lengths come from the design.
