If a garage floor is going to be reinforced, rebar on chairs generally beats wire mesh, because it stays where it's placed and adds more steel to the slab. But for an ordinary garage floor on the ground in Ontario, Part 9 of the 2024 Ontario Building Code doesn't require reinforcement at all. It sets a minimum thickness, the concrete strength and drainage. Reinforcement becomes a design decision, and in some cases, such as a garage slab over a basement or a floor carrying a hoist, an engineering requirement.
What the Ontario Building Code says about garage floors
For a garage serving one dwelling unit, the relevant rules are spread across a few parts of the 2024 OBC (O. Reg. 163/24):
| Rule | Where | What it says |
|---|---|---|
| Minimum thickness | Article 9.16.4.3 | Concrete floor slabs at least 75 mm thick, exclusive of topping |
| Concrete strength | Article 9.3.1.6 | At least 32 MPa at 28 days for garage floors, carport floors and exterior flatwork |
| Water to cementing materials ratio | Article 9.3.1.7 | No more than 0.45 for garage and carport floors |
| Air entrainment | Sentence 9.3.1.6.(2) | 5 to 8% for site-batched concrete in garage floors |
| Granular fill | Sentence 9.16.2.1.(2) | The 100 mm granular layer required under other floors need not be installed under garage slabs |
| Drainage | Article 9.35.2.2 | An attached or built-in garage floor must slope to drain liquids to the outdoors |
| Joint with the house | Sentence 9.35.3.2.(2) | With slab-on-ground construction, a construction joint between the house slab and an attached garage slab |
None of these require reinforcing steel in a garage floor on the ground. Two other rules decide when the slab stops being "ordinary":
- Floors that support the structure. Article 9.16.1.2 says floors-on-ground that support loads from the superstructure must be designed under Part 4. A slab that carries walls or posts falls in this group.
- Garage slabs over a basement or cold room. The OBC's prescriptive reinforced slab for basement cold rooms (Section 9.40) specifically does not apply to slabs intended to support motor vehicles. A suspended garage slab over living space or storage is engineered.
That's a big part of the answer to "rebar or mesh for a garage floor?": on grade, it's the designer's or builder's choice; over a basement, it's an engineer's design, and that design will specify rebar.
Mesh vs rebar in a garage slab
| Welded wire mesh | Rebar | |
|---|---|---|
| Common residential product | 152x152 MW9.1 or MW18.7 (6x6 10/10 or 6/6) | 10M bars in a grid, sometimes 15M |
| Steel per metre width | About 60 to 125 mm² for those mesh sizes | 250 mm² for 10M @ 400 mm |
| Staying at the right depth | Hard; light mesh needs supports at 0.8 m or less | Easier with chairs |
| Point loads (jacks, stands, lifts) | Limited help | Can be detailed for thickened or heavier areas |
| Tying to foundation or other slabs | Limited | Dowels and bent bars detailed as needed |
The mesh steel areas and support spacing come from Concrete Ontario's reinforced concrete reference guide. A 10M bar has an area of 100 mm², so at 400 mm spacing it gives 250 mm² of steel per metre each way, about twice the heavier of the two common mesh sizes.
The bigger difference is placement. Shrinkage cracks start at the top of a slab, so steel in a slab on grade belongs in the middle to upper part, not lying on the ground. Light mesh is hard to keep there because it bends under foot traffic. Rebar on chairs holds its height through the pour. For a broader look, see wire mesh vs rebar vs fibre for concrete slabs.
Why garage floors get reinforced anyway
Even when the code doesn't require it, builders and designers often reinforce garage slabs because garages see things a basement floor doesn't:
- Heavy, concentrated loads from car tires, floor jacks, jack stands, storage racks and workshop equipment.
- Water and salt carried in on vehicles all winter, which is hard on concrete and on any steel near the surface.
- Uneven support, especially on backfill next to a new foundation, where the base can settle.
- Joints with the house and the driveway, where dowels or tie bars may be specified.
Reinforcement helps hold cracks tight and keeps panels level, but it doesn't replace a good base, the right concrete, curing and properly spaced control joints. For a garage slab, those come first. If your garage floor is getting plain concrete, the joint layout is the most important detail to get right.
Rebar spacing for a concrete garage floor
When a garage slab is reinforced, the drawings give the bar size and spacing as a callout such as 10M @ 400 EW (10M bars at 400 mm centres, each way). Heavier loads may get closer spacing or 15M bar, and engineered slabs may have extra bars at thickened edges, openings and drains. Our guide to rebar spacing for concrete slabs explains the callouts and the limits on spacing.
Worked example: a 6.1 m x 6.1 m (20 ft x 20 ft) garage slab with 10M @ 400 EW. Assume the bars stop 50 mm short of each edge; your drawings set the actual edge cover.
- Usable width: 6,100 minus 100 = 6,000 mm
- Spaces: 6,000 ÷ 400 = 15, so 16 bars each way
- Bar length: about 6.0 m
- Total: 16 x 2 x 6.0 = 192 m of 10M
- Weight: 192 x 0.785 kg/m = about 151 kg before any laps, dowels or edge bars
At 6.0 m, the bars are still a single length, so this layout needs no lap splices. Larger garages or longer bars may.
Common garage slab cases
Detached garage on its own slab. Article 9.35.3.1 lets a small detached garage (under 55 m², one storey, not masonry or masonry veneer) sit on a concrete slab at least 100 mm thick instead of conventional foundations. How that slab is detailed, including any thickened edges and reinforcement, should come from the designer or the drawings submitted for the permit.
Attached garage with a house foundation. The garage floor is a separate slab on ground, sloped to drain outdoors, with a construction joint at the house slab. Reinforcement is a design choice unless the drawings call for it.
Garage over a basement. Engineered suspended slab, always reinforced to the engineer's design. Expect bar lists, top and bottom steel and specified cover for salt exposure.
Car lift or heavy equipment. Check the lift manufacturer's slab requirements before installing. An engineer may need to design a thickened, reinforced pad.
Our post on slab-on-grade rebar requirements goes into code rules for other slabs on grade. For the outdoor slab that usually meets the garage, see wire mesh vs rebar for a concrete driveway.
Ordering rebar for a garage floor
If your garage slab calls for rebar, send us the drawings or the slab size with bar size and spacing and we'll quote it, with bars cut to length and bundled so your crew can place them without cutting on site. We can also prepare the bar list from your structural drawings. See our rebar products for straight bar, dowels and fabricated shapes.
Frequently asked questions
Is rebar or wire mesh better for a garage floor?
If the garage slab is reinforced, rebar on chairs is generally the better choice. It holds its position during the pour and adds more steel than common mesh. Mesh only works if it is properly supported at the right height across the whole slab.
Does a garage floor need rebar in Ontario?
An ordinary garage floor on the ground isn't required to be reinforced under Part 9 of the 2024 Ontario Building Code. It needs at least 75 mm thickness, 32 MPa concrete and, for an attached garage, a slope to drain outdoors. Slabs that carry structural loads or span over a basement are designed by an engineer.
What is the typical rebar spacing for a concrete garage floor?
Spacing comes from the drawings or the designer, written as a callout like 10M @ 400 EW (10M bars at 400 mm centres each way). Closer spacing or 15M bar is used for heavier loads. The bars must sit on chairs in the slab, not on the ground.
Can I put a car lift on a garage slab?
Check before you buy. Lifts put large concentrated loads on their anchor points, and manufacturers specify minimum slab thickness and concrete strength. An ordinary garage slab may not meet those, and an engineer may need to design a thickened or reinforced area.
