Rebar in a footing should overlap by the lap length shown on your structural drawings. On engineered work in Canada that length comes from CSA A23.3, and a standard Class B lap for uncoated Grade 400 bottom bars in 30 MPa concrete works out to about 390 mm for 10M and 550 mm for 15M. At corners and intersections, the bars are made continuous with bent L-shaped corner bars that lap with the straight bars on each side, so the steel does not simply stop where two footings meet.
This post covers footing laps and corner details specifically. Whether a footing needs rebar at all is covered in do footings need rebar, and bar sizes and quantities in rebar for footings.
How much rebar should overlap in footings
There are two situations, and they give different answers.
Plain Part 9 strip footings. The 2024 Ontario Building Code does not require reinforcement in ordinary strip footings for houses and small buildings, so it also sets no lap length for them. If a designer adds bars to a Part 9 footing, the lap on the drawings is the one to use. If the drawings show bars but no lap, ask the designer rather than guessing.
Designed (engineered) footings. Lap length is calculated under CSA A23.3. Footing bars sit near the bottom of the concrete, so they normally count as bottom bars, without the 1.3 top-bar factor. Using the simplified method, a Class B splice and uncoated Grade 400 bar:
| Bar | 25 MPa | 30 MPa | 35 MPa |
|---|---|---|---|
| 10M | 430 mm | 390 mm | 390 mm |
| 15M | 600 mm | 550 mm | 510 mm |
| 20M | 740 mm | 670 mm | 620 mm |
| 25M | 1,180 mm | 1,080 mm | 1,000 mm |
These values assume the cover, spacing and confinement conditions that the simplified method needs. Where they are not met, laps get one third longer. Epoxy-coated bar, Grade 500 bar and top mats in deep footings (more than 300 mm of fresh concrete below them) all need longer laps. Our lap splice length chart lists every assumption and the other cases.
A few things to notice:
- "40 bar diameters" is not a code rule. For 25M bar it would give about 1,010 mm, shorter than the 1,080 mm in 30 MPa concrete.
- The jump from 20M to 25M is real. CSA A23.3 gives smaller bars a 0.8 size factor, so 25M laps are much longer than 20M laps.
- Mixed sizes lap on the smaller bar. RSIC standard practice is that when two bar sizes are lapped, the lap is based on the smaller bar but is not less than the development length of the larger one, unless the drawings say otherwise.
Where laps go and how they are placed
Laps happen wherever a run of footing is longer than a bar. Standard mill lengths are 12 m for 10M and 18 m for 15M and larger, but bars are often cut shorter for handling and delivery, which adds laps.
Staggering. Engineers often ask for laps in adjacent bars to be offset so they do not all fall at the same section. If the drawings call for staggered laps, the bar lengths on the list will alternate, and the crew needs to place the right length in the right line.
Contact or non-contact. Lapped bars do not have to touch. CSA A23.3 allows non-contact laps in flexural members as long as the bars are no farther apart than one fifth of the required lap length or 150 mm, whichever is less. For a 550 mm 15M lap that limit is 110 mm. In practice most crews tie lapped bars side by side because it is the easiest way to hold them in place.
Cover at the lap. Two bars side by side take more room than one. In a narrow footing, check that the lapped pair still has the bottom and side cover the drawings require. For concrete cast against earth, CSA A23.1 cover is 75 mm.
Tying. RSIC standard practice does not require a tie at every intersection, but bent ends in footings and mats are commonly held with saddle ties so they do not rotate out of position during the pour.
Corner bars: keeping footing steel continuous
A rectangular building has four corners, and an L-shaped or stepped plan has many more. Two straight bars that simply stop where two footings meet leave a break in the reinforcement right where the footing changes direction. Drawings deal with it in one of two ways.
Corner splice bars
Separate bent L-bars are placed at the corner, one for each line of continuous bars. Each leg laps with the straight bar running in that direction.
- RSIC standard practice for wall corners, and the same logic applies to footings, is that corner bars are the same size and spacing as the bars they join.
- Each leg is a full lap length measured from the corner, so a 15M corner bar with 550 mm laps has two legs of about 550 mm plus the bend allowance.
- This method uses a little more steel, but the straight bars stay straight and the corner bars arrive ready to drop in. RSIC notes the extra material is often offset by easier fabrication and placing.
Continuous corner bars
The continuous bars themselves are bent around the corner, so one leg of the long bar becomes part of the next run. It uses less steel, but bent long bars are awkward to handle and place, and a small error in one run pushes the bend off the corner.
RSIC treats both methods as acceptable when the engineer has not shown a detail. Where the drawings specify one method, switching to the other needs the engineer's approval.
T-intersections and interior footings
Where an interior footing meets an exterior one in a T, the bars of the stem footing need to be anchored into the through footing. The usual detail is again an L-bar or a hooked bar end that extends across the through footing, with its leg lapping the stem bars. Bearing wall footings, garage footings and porch footings that tie into the main foundation are where intersection bars get missed most often.
Steps
Stepped footings are limited in Part 9 to a 600 mm rise with at least 600 mm between steps (Article 9.15.3.9). When reinforced, the bars either bend through the step or are lapped with bent bars at each riser, as the details show. Each step adds bent pieces to the bar list.
Why corner bars are not bent on site
Bending a 15M bar into a tight L by hand is hard to do accurately, and bends made with a pipe or a pry bar often end up with the wrong radius or a kink. Minimum bend diameters exist to protect the bar and the concrete inside the bend; our post on rebar hooks and bend radius covers them. Shop-bent corner bars come out at the correct diameter, with consistent legs, tagged for the corner they belong to.
If you do have to deal with a missed corner bar on site, our post on bending and cutting rebar on site explains what is and is not good practice.
Counting laps and corner bars on a bar list
Laps and corner bars are the two items most often left out of a rough footing estimate. For a simple rectangular footing with two continuous lines of 15M bar and 550 mm laps:
- Corner bars: 4 corners × 2 bar lines = 8 L-bars, each with two 550 mm legs, roughly 1.1 m of 15M per bar before the bend allowance.
- Laps: each splice adds one lap length, 550 mm, per bar line. A footing run long enough for three splices per line adds about 3.3 m across both lines.
- Steps, bump-outs and T-intersections each add their own bent bars and laps.
None of this is large on its own, but on a house with a garage, porch and several steps it adds up, and it is exactly the steel that is missing when a crew runs short. A bar list detailed from the drawings counts every one.
Getting footing bars detailed and bent
The lap lengths and corner details on your structural drawings decide what goes on the bar list. If the drawings only say "lap per CSA A23.3" or show a typical corner without dimensions, get the engineer to confirm the concrete strength and lap class before the bars are cut.
We prepare footing bar lists with laps worked out from your drawings, then cut, bend and tag straight bars, corner bars and dowels to their marks. Send us your foundation drawings for a free take-off and quote, or see our services for detailing and cut and bend.
Frequently asked questions
How much should rebar overlap in footings?
As much as the structural drawings say. On engineered work the lap comes from CSA A23.3; a standard Class B tension lap for uncoated Grade 400 bottom bars in 30 MPa concrete works out to about 390 mm for 10M and 550 mm for 15M. Plain Part 9 strip footings have no code-set lap because the code does not require rebar in them.
Is 40 bar diameters enough for a footing lap?
Not always. 40 bar diameters is a rule of thumb, not a CSA requirement. Calculated laps for Grade 400 bar range from about 32 to over 60 bar diameters depending on bar size, concrete strength and position, so use the length on your drawings.
Do lapped bars in a footing have to touch?
No. CSA A23.3 allows non-contact laps in flexural members as long as the bars are no farther apart than one fifth of the required lap length or 150 mm, whichever is less. Most crews tie lapped bars side by side anyway because it holds them in position.
How do you do rebar corners in a footing?
Either with separate L-shaped corner bars that lap with the straight bars on both sides, or by bending the continuous bars around the corner. Corner bars are the same size and spacing as the bars they join, and each leg is long enough for a full lap.
