Rebar in a concrete block wall is a grid: vertical bars in grouted cells at the spacing set by the code table or the designer, and horizontal steel in bond beams and bed-joint reinforcement. For reinforced block foundation walls under Part 9 of the 2024 Ontario Building Code, Table 9.15.4.2.-B sets the vertical bars, for example one 15M bar at 1,600 mm in a 190 mm wall with 1.4 m of backfill, and the code requires a 15M bond beam at the top of the wall plus ladder or truss reinforcement in every second course. Every cell that holds a bar has to be filled solid with grout, or the steel does nothing.
This post covers where the bars go, how spacing is set, how the walls are grouted and how to get the steel ordered. Poured concrete and ICF foundation walls are covered in our foundation wall rebar guide.
Which block walls need rebar
Not every block wall is reinforced. The 2024 OBC (O. Reg. 163/24) splits them like this:
| Wall | Where the rebar rules come from |
|---|---|
| Unreinforced block foundation wall within Table 9.15.4.2.-A | No rebar required |
| Block foundation wall beyond those limits, laterally supported at the top | Table 9.15.4.2.-B and Sentences 9.15.4.2.(4) to (7) |
| Above-grade loadbearing masonry in higher seismic zones | Subsection 9.20.15, when triggered by Article 9.20.1.2 |
| Retaining walls, tall walls, commercial and industrial walls | Engineered design to CSA S304 |
Table 9.15.4.2.-A limits unreinforced block walls to fairly low backfill heights. A 190 mm unreinforced block wall up to 2.5 m high and laterally supported at the top, for instance, is limited to 1.2 m of finished ground above the basement floor. Deeper basements in block need reinforcement or a design.
Article 9.20.1.2 requires the minimum earthquake reinforcement of Subsection 9.20.15 for loadbearing masonry in buildings over 1 storey where the seismic value Sa(0.2) is greater than 0.55, and for 3-storey masonry buildings where it is greater than 0.35. Your designer looks up the value for your municipality in MMAH Supplementary Standard SB-1.
Retaining walls are a common source of confusion. Part 9's foundation wall tables do not cover freestanding garden or retaining walls, and under Division A of the OBC (Article 1.3.3.2), Part 4 design applies to a retaining wall more than 1,000 mm in exposed height next to public property, access to a building, or private property the public is admitted to.
Vertical rebar spacing in block foundation walls
For a reinforced block foundation wall within Part 9, Table 9.15.4.2.-B applies where the wall is laterally supported at the top, the soil is average and stable, and wind on the exposed part of the foundation is no greater than 0.70 kPa. The table sets the bar size and spacing by wall thickness, wall height and the height of finished ground above the basement floor.
An excerpt for a 190 mm wall:
| Finished ground above basement floor | Wall height 2.5 m | Wall height 3.0 m |
|---|---|---|
| 1.0 m | No reinforcement required | 1-15M at 1,800 mm |
| 1.4 m | 1-15M at 1,600 mm | 1-15M at 1,600 mm |
| 1.8 m | 1-15M at 1,400 mm | 1-15M at 1,200 mm |
| 2.2 m | 2-15M at 1,200 mm | 2-15M at 1,000 mm |
| 2.4 m | 2-15M at 1,000 mm | 2-15M at 800 mm |
For 240 mm walls the table uses 20M bars, for example 1-20M at 1,400 mm with 2.2 m of backfill. Read the full table for your exact wall; several rows give a choice between two arrangements, and some combinations are not permitted at all.
On top of the tabulated spacing, Sentence 9.15.4.2.(4) requires continuous vertical bars at:
- wall corners, wall ends and wall intersections
- changes in wall height
- the jambs of all openings
- movement joints
These bars run from the top of the footing to the top of the wall. Where the wall is supported at the top but the floor slab does not support it at the base, they need at least 50 mm of embedment into the footing. Sentence 9.15.4.2.(6) puts all vertical bars on the centre line of the wall.
Horizontal reinforcement: bond beams and joint reinforcement
Horizontal steel in a reinforced block foundation wall comes in two forms.
Bond beams. Sentence 9.15.4.2.(5) requires a continuous horizontal bond beam with at least one 15M bar:
- along the top of the wall
- at the sill and head of all openings wider than 1.20 m
- at structurally connected floors
A bond beam is a course of special blocks with the webs cut down or knocked out, so a horizontal bar can sit in a continuous channel that is then grouted solid. At corners, the bond beam bar needs a bent corner bar or a lap so it is continuous around the wall.
Joint reinforcement. Sentence 9.15.4.2.(7) requires ladder- or truss-type reinforcement, not less than 3.8 mm in diameter (No. 9 ASWG), in the bed joint of every second course. This is prefabricated wire laid in the mortar, not loose rebar.
Over wide openings, the bond beam at the head often works with a lintel. Our post on steel lintels for concrete block walls covers that side of it.
Putting the rebar in the cells
The order of work matters, because once a cell is grouted there is no adjusting the bar.
- Dowels from the footing. Vertical bars are usually started from dowels cast into the footing at the bar spacing, lined up with the cells they will occupy. Lay out the block coursing before the footing pour so the dowels land in cells, not webs.
- Lay the block. Under Article 9.20.4.2, the webs next to cells that will be grouted are laid in a full bed of mortar, so grout cannot leak sideways into empty cells. Keep mortar droppings and fins out of the cells that will be grouted.
- Set the vertical bars. Lap them with the footing dowels at the lap length on the drawings, and hold them centred in the cell (or where the design puts them) with bar positioners at intervals up the wall.
- Place bond beam bars in the bond beam courses, lapped at splices and bent at corners.
- Grout. Fill the reinforced cells and bond beams solid.
Bars that are too long to handle through the full wall height are often set in shorter pieces with laps, or the block is threaded over the bars as the wall goes up. Your mason will have a preference; tell your rebar supplier which, because it changes the bar lengths.
Grouting reinforced block walls
Grout is what makes the bar and the block act together. Without it, a bar standing in an empty cell carries almost nothing.
For reinforced block foundation walls, Article 9.15.2.2 of the OBC requires:
- concrete block conforming to CSA A165.1 with at least 15 MPa compressive strength
- Type S mortar to CSA A179
- coarse grout to CSA A179
- grout placement in accordance with CSA A371
Article 9.20.3.2 adds that grout must be mixed with enough water to fill all voids completely without excessive segregation or bleeding.
CSA A371 governs how grout is placed, including how high it is poured at a time and how it is consolidated. Those limits decide whether the wall is grouted in stages as it rises or in taller lifts with cleanouts at the base. Your mason and designer apply the standard; what matters for the steel is:
- bars are clean and centred before grouting
- cells around bars are clear of mortar droppings
- the grout is consolidated so there are no voids around the bars
- the bar is not disturbed once grout starts to set
Ordering steel for a block wall
A block wall bar list is short but fussy: footing dowels, verticals cut to suit the lift heights and laps, bond beam bars, corner bars and jamb bars at openings. Getting the lengths to match the coursing and the mason's grouting sequence saves cutting on site. Our post on masonry and CMU rebar shop drawings explains how block wall steel is detailed.
Joint reinforcement (ladder and truss wire) is a masonry accessory usually bought through masonry suppliers.
Get block wall rebar cut to your drawings
We prepare take-offs and bar lists from your drawings and cut and bend 10M to 55M bar, including footing dowels, verticals, bond beam bars and corner bars, tagged by wall and delivered across the GTA and Ontario. Questions about how a wall should be reinforced belong with your designer or engineer; we build the steel to the drawings.
Send your foundation or wall drawings for a free take-off and quote, or see our rebar products.
Frequently asked questions
What is the vertical rebar spacing in a concrete block wall?
For reinforced block foundation walls under Part 9 of the 2024 Ontario Building Code, Table 9.15.4.2.-B sets it by wall thickness, wall height and backfill height. In a 190 mm wall it ranges from no bars for low backfill to 15M bars at 1,800 mm down to pairs of 15M bars at 800 mm for deep backfill. Other block walls are designed and the drawings set the spacing.
What is the horizontal rebar spacing in a block wall?
In reinforced Part 9 block foundation walls, horizontal steel is a bond beam with at least one 15M bar at the top of the wall, at the sill and head of openings wider than 1.2 m and at structurally connected floors, plus ladder or truss joint reinforcement of at least 3.8 mm wire in every second course.
Do block wall cells with rebar have to be grouted?
Yes. Rebar in a block wall works only when the cell around it is filled solid with grout. For reinforced block foundation walls the OBC calls for coarse grout to CSA A179, placed in accordance with CSA A371.
Where does the rebar go in a concrete block cell?
For reinforced Part 9 block foundation walls, the OBC requires vertical bars along the centre line of the wall. In designed walls the bar position comes from the drawings; some designs place bars toward one face.
Do block foundation walls need rebar in Ontario?
Not always. Unreinforced block foundation walls are allowed within the limits of OBC Table 9.15.4.2.-A. Beyond those backfill heights, the wall must be reinforced to Table 9.15.4.2.-B or designed.
