A rebar dowel has to be long enough to develop the bar on both sides of the joint. On engineered work in Canada, that means the CSA A23.3 development length into the first pour, plus a lap or development length into the second, so the total dowel length is roughly the sum of the two. A straight 15M dowel in 30 MPa concrete needs about 430 mm of tension development on each side under the simplified method, while a hooked 15M dowel can get by with about 300 mm of embedment. Small buildings under Part 9 of the Ontario Building Code have their own fixed minimums, such as 300 mm on each side of a cold joint in a flat ICF foundation wall.
This post covers how dowel length is set, with worked values for 10M to 35M, and the different rules for cast-in and drilled-in dowels.
What a rebar dowel has to do
A rebar dowel is a deformed bar that crosses a joint between two pours: footing to wall, wall to slab, an old slab to a new one, a column to its footing. Its job is to carry force across that joint, in tension, compression or shear.
To do that, each end of the dowel needs enough embedment to grip the concrete. Too short, and the bar pulls out or splits the concrete before it reaches its strength. That required grip length is the development length.
This is different from a smooth dowel bar in a slab-on-grade or pavement joint, which is meant to let the joint move. Those are sized by the slab or pavement design, not by development length. Our post on dowel bars vs rebar explains the difference.
How dowel length is worked out
A typical cast-in dowel has two parts:
- Embedment into the first pour. Usually a development length, straight or hooked. For a wall dowel, this is the length into the footing.
- Projection into the second pour. Usually a lap splice with the bars in the second pour, or a development length if the dowel just anchors into the new concrete.
Total dowel length = embedment + projection (plus the hook, for hooked dowels).
Straight dowels
CSA A23.3 Clause 12.2 sets the tension development length. Using the simplified method (Clause 12.2.3), Grade 400 uncoated bar, normal-density concrete, bars not classed as top bars, and ld not less than 300 mm:
| Bar | Straight ld, 25 MPa | Straight ld, 30 MPa | Class B lap (1.3 ld), 30 MPa |
|---|---|---|---|
| 10M | 330 mm | 300 mm | 390 mm |
| 15M | 470 mm | 430 mm | 550 mm |
| 20M | 570 mm | 520 mm | 670 mm |
| 25M | 910 mm | 830 mm | 1,080 mm |
| 30M | 1,080 mm | 990 mm | 1,280 mm |
| 35M | 1,290 mm | 1,180 mm | 1,530 mm |
Values are rounded up to the next 10 mm. The simplified method only applies where cover, spacing and confinement meet A23.3's minimums; otherwise the 0.6 coefficient applies and lengths grow by one third. Epoxy coating, top-bar position and 500W bar all increase the length. Our lap splice chart lists the assumptions in full, and rebar development length explains the factors.
So a straight 15M dowel from a footing into a wall, lapped with the wall verticals, would be about 430 mm into the footing plus 550 mm of lap: roughly 1 m long in total under these assumptions. That is why straight dowels often do not fit in a shallow footing.
Hooked dowels
A standard hook develops a bar in a much shorter embedment, which is why footing dowels are usually hooked and sit on the bottom mat. CSA A23.3 Clause 12.5 gives a basic hook development length of 100 db ÷ √f'c for Grade 400 bar, not less than 8 bar diameters or 150 mm, before any modification factors:
| Bar | Hooked ldh, 25 MPa | Hooked ldh, 30 MPa |
|---|---|---|
| 10M | 230 mm | 210 mm |
| 15M | 320 mm | 300 mm |
| 20M | 390 mm | 360 mm |
| 25M | 510 mm | 470 mm |
| 30M | 600 mm | 550 mm |
| 35M | 720 mm | 660 mm |
The hook length is measured from the joint face to the outside of the hook. Modification factors can reduce it (for example, generous side cover or ties around the hook) or increase it (1.2 for epoxy-coated bar, and a factor for bar stronger than Grade 400). The footing also has to be deep enough for the hook plus bottom cover; our concrete cover guide has the cover values.
Hooks only help in tension. A23.3 does not count hooks as effective for developing bars in compression.
Compression dowels
Column dowels into footings are often designed for compression. A23.3 sets compression development length as the larger of 0.24 db fy ÷ √f'c and 0.044 db fy, and not less than 200 mm. For Grade 400 bar that works out to about 310 mm for 15M and 490 mm for 25M in 25 MPa concrete. Whether a dowel can be detailed for compression only is the engineer's call.
Dowel minimums in the Ontario Building Code (Part 9)
Houses and small buildings designed under Part 9 of the 2024 Ontario Building Code use prescriptive rules in a few places. The ones that involve dowels:
- Cold joints in flat ICF foundation walls must be reinforced with at least one 15M bar at not more than 600 mm on centre, embedded not less than 300 mm on both sides of the joint (Article 9.15.4.5).
- Flat ICF foundation walls dowelled to the footing are considered laterally supported at the bottom when the dowels are at least 15M at not more than 1.2 m on centre, or 10M at not more than 600 mm on centre (Article 9.15.4.4). This is one of three ways to meet that condition, along with low backfill or a shear key.
- Reinforced slabs over cold rooms must be anchored to the foundation walls with 600 mm × 600 mm 10M bent dowels at not more than 600 mm on centre (Article 9.40.1.4).
Outside those cases, reinforced concrete that falls under Part 4 is designed to CSA A23.3. Our overview of rebar code requirements in Ontario shows how Part 9 and A23.3 fit together.
Drilled-in dowels into existing concrete
When new concrete is tied to old, dowels are usually drilled and set in adhesive (often called epoxy dowels, though not all adhesives are epoxy). Here the cast-in development length tables do not apply directly:
- The adhesive system governs. Capacity depends on the adhesive, hole diameter, cleaning, embedment, edge distance, spacing and the strength and condition of the existing concrete. Manufacturers publish design data for their systems.
- The design standard is CSA A23.3 Annex D. Annex D covers cast-in anchors and post-installed mechanical and adhesive anchors, including reinforcing bars set in adhesive. It became a mandatory part of the standard in the 2019 edition, the one referenced by the 2024 OBC, and it includes installation and inspection requirements and the need for qualified installers.
- Installation matters as much as length. A dowel at full depth in a dusty or wet hole can carry far less than its rating. Follow the manufacturer's cleaning, temperature and cure-time instructions exactly.
- Watch for existing rebar. Drilling through existing bars can weaken the structure. Scanning before drilling is common practice.
For anything structural, the engineer specifies the bar, the embedment and the adhesive. Rules of thumb like "embed 10 bar diameters" or "drill 6 inches" are not a substitute.
Ordering dowels
Dowels are one of the easiest items to get wrong on a bar list, because the length depends on what happens at both ends. When you order them:
- Give the total length and shape, including the hook and the projection, not just the embedment.
- Confirm the hook direction and whether the dowel sits on the bottom mat or is hung from a template.
- Account for laps above. If the next pour's bars lap with the dowels, the projection must match that lap length.
- Separate coated and uncoated dowels, since coating changes both the length and the order.
We supply fabricated dowels and stirrups in 10M to 55M, detailed from your drawings, bent, tagged by mark and delivered across the GTA and Ontario. Send us your drawings for a free take-off and quote, or see our rebar products.
Frequently asked questions
How long should dowels be in concrete?
Long enough to develop the bar on both sides of the joint. On engineered work that means the CSA A23.3 development length into the first pour plus a lap or development length into the second. For example, a straight 15M bar in 30 MPa concrete needs about 430 mm of tension development on each side under the simplified method.
How deep should rebar dowels be?
Embedment depth comes from the drawings. Cast-in dowels use CSA A23.3 development length, straight or hooked. Drilled-in dowels use the adhesive manufacturer's design data. Under OBC Part 9, cold joints in flat ICF foundation walls need 15M dowels embedded at least 300 mm on each side.
Can I dowel rebar into existing concrete?
Yes, by drilling and setting the bar in an approved adhesive system. The embedment, hole size, cleaning and curing come from the engineer and the adhesive maker's data, and post-installed anchors are designed under CSA A23.3 Annex D.
What is the minimum length of a dowel bar?
For deformed rebar dowels in tension, CSA A23.3 sets development length at not less than 300 mm per side, and hooked bars at not less than 8 bar diameters or 150 mm. Smooth pavement dowel bars are a different product sized by the pavement design.
