Most concrete steps are reinforced with rebar, but how much depends on how the steps are supported. A small block of steps poured on grade may only need a light grid of 10M or 15M bars to hold cracks tight, while a stair slab spanning between supports, or steps cantilevered from a foundation wall, needs steel designed for the loads. In Ontario, Article 9.8.9.2 of the 2024 Building Code requires exterior concrete stairs with more than 2 risers and 2 treads to sit on concrete or masonry walls or piers at least 150 mm in cross-section, or to be cantilevered from the foundation wall.
Front steps, porch steps and walkout stairs crack, settle and pull away from houses all over the GTA. The steel inside them, and how they're tied to the house or kept apart from it, has a lot to do with that.
The three ways concrete steps are supported
How the rebar is laid out starts with how the steps are carried.
| Type | How it's supported | Rebar role |
|---|---|---|
| Solid steps on grade | Fill or a thickened slab on compacted ground | Crack control; holding the block together |
| Steps on walls or piers | Concrete or masonry walls or piers on footings | Stair slab spans between supports; main bars carry the load |
| Cantilevered steps | Anchored to the house foundation wall | Designed reinforcement and anchorage into the wall |
The code rules. Under Article 9.8.9.2 of the 2024 OBC, exterior concrete stairs with more than 2 risers and 2 treads must be supported on unit masonry or concrete walls or piers not less than 150 mm in cross-section, or cantilevered from the main foundation wall. The depth of foundations for exterior steps has to follow Section 9.12, which deals with excavation and frost. Steps of 2 risers or fewer, such as a single step at a door, are often simply poured on a compacted base.
For cantilevered steps, Subsection 9.8.10 adds that the steps and their anchorage must be designed and installed to support the loads, that they be anchored to concrete foundation walls at least 200 mm thick, and that precautions be taken during backfilling and grading so freezing soil doesn't push up on the underside of the steps and damage them or the wall.
Concrete stairs also have to meet the same dimensional rules as any other stair. For stairs serving a single house, Table 9.8.4.1 allows a maximum rise of 200 mm and a minimum run of 255 mm. Our Ontario Building Code stair rules post covers rise, run, width and headroom, and guard and handrail rules covers the railings that often go on top.
Rebar in solid steps on grade
A block of two or three steps poured on a compacted granular base is the simplest case. The concrete is mostly mass, and the steel's job is to hold shrinkage and frost cracks tight so the steps don't break into pieces.
A typical layout:
- A bottom grid of 10M or 15M bars each way, on chairs above the base, much like a small pad. Our guide to rebar for concrete pads covers grid spacing and placement.
- Bent bars following the profile of each step, so steel runs up the risers and along the treads near the surface.
- Bars along each nosing to help hold the front edge, which is where steps chip and spall first.
- Cover suited to the exposure. Exterior steps see freeze-thaw and de-icing salt, so they need more cover than interior concrete. The minimums by exposure class are in our concrete cover guide.
Where steps fill a large volume, contractors often reduce the concrete with compacted fill inside the forms, leaving a reinforced shell. That changes how the steel should be laid out, so it's worth having the detail drawn.
Rebar in a stair slab
When steps span between supports, such as between a landing and a footing at grade, or between two walls, they act as a sloped slab (often called the waist) with the steps formed on top. That slab bends under load, so the steel works like a slab's:
- Main bars run along the length of the stair, near the bottom of the sloped slab where it's in tension, and continue into the landing and the support at the bottom.
- Distribution bars run across the width of the stair, tied to the main bars.
- Top bars are added where the slab is continuous over a support or meets a landing, because the top is in tension there.
- Bends at the landing and the base are formed so bars don't straighten out and pop through the concrete at the inside corner.
The sizes, spacing and laps for a stair slab come from the designer, not a rule of thumb. Interior concrete stairs in larger buildings are designed for heavier loads than house stairs. Article 9.8.9.1 sets design loads of 1.9 kPa for stairs serving a single dwelling unit or a house with a secondary suite and 4.8 kPa for other stairs in Part 9 buildings.
Our bent rebar shapes guide shows the step bars, offsets and L-bars that stair detailing uses.
Dowel bars for stairs
"Dowel bars for stairs" can mean two different things.
Dowels that tie new to existing concrete. Rebuilding steps against an existing landing, porch slab or wall often means drilling holes and setting rebar dowels with an adhesive anchoring system, so the new pour is tied to the old. The engineer or product data sets the bar size, embedment and hole size. See how to dowel rebar into existing concrete for how it's done properly.
Dowels that tie the steps to the house. This is where many step problems start. The house foundation sits below frost. Steps on a shallow base on grade move up and down with frost. Doweling those steps rigidly to the house wall locks two things together that want to move separately, and the steps crack at the connection or pull on the wall. Many designers either:
- Isolate the steps from the house with a joint so they float on their own, or
- Support them properly, on their own foundations taken to frost depth or cantilevered from a foundation wall at least 200 mm thick, with designed anchorage.
Which one suits your house is a design decision. If you're replacing steps that heaved, find out why before choosing the new detail.
Repairing or replacing concrete steps
Common problems and what they usually mean:
- Steps pulling away from the house: settlement or frost movement of steps that aren't on frost-depth foundations
- Cracks through the steps: shrinkage or movement with too little or poorly placed steel
- Spalling nosings and exposed rebar: too little cover, salt exposure and freeze-thaw. See how to cover and repair exposed rebar.
- Rust stains: steel corroding close to the surface
Patching works for surface damage. Steps that have moved or broken through usually need to come out and be rebuilt on a proper base or supports, with the steel detailed to suit. For steps attached to a house wall or carrying a porch, involve a designer.
If you're weighing alternatives, steel stairs vs concrete stairs compares the two for exterior use, and steel is often lighter on the foundation for a walkout or deck stair.
Ordering rebar for steps
Step reinforcement is mostly bent bars: L-bars at the base, step-profile bars, nosing bars and landing bars. Bending them on site with a hand bender takes time and it's hard to keep each shape the same. Shop-bent bars arrive tagged to a bar list so each piece goes in its place.
To get an accurate quote, send:
- the drawings or a sketch with the stair width, number of risers, rise and run, and landing size
- the support type (on grade, on walls or piers, or cantilevered)
- the bar sizes and spacing from the designer, if you have them
We supply straight bars cut to length and fabricated bent shapes, dowels and stirrups in sizes 10M to 55M, tagged and bundled per your bar list, with delivery across the GTA and Ontario. We also prepare bar lists from your drawings. Send us your drawings for a free take-off and quote, and see our rebar products for what we supply.
Frequently asked questions
Do you need rebar in concrete steps?
Small solid steps on grade are sometimes poured plain, but most concrete steps are reinforced to hold cracks tight and tie the steps together. Stair slabs that span between supports, and steps cantilevered from a foundation wall, need reinforcement designed for the loads.
What does the Ontario Building Code say about exterior concrete steps?
Article 9.8.9.2 of the 2024 OBC says exterior concrete stairs with more than 2 risers and 2 treads must be supported on unit masonry or concrete walls or piers at least 150 mm in cross-section, or cantilevered from the main foundation wall. Their foundations must meet the depth requirements in Section 9.12.
Should concrete steps be doweled to the foundation wall?
It depends on the design. Cantilevered steps are anchored to the foundation wall, which must be at least 200 mm thick. Steps on their own foundations are often isolated from the house so they can move separately. Doweling steps on grade to a wall that doesn't move with frost can crack them, so follow the designer's detail.
What size rebar is used in concrete steps?
Residential steps commonly use 10M or 15M bars, with bent bars following the stair profile and straight bars across the width. The size and spacing for a stair slab or cantilevered steps come from the designer's drawings.
