What's the right rebar size for an Ottawa concrete driveway?

For Ottawa concrete driveways, #4 rebar (12.7mm diameter) spaced 18 to 24 inches on center in both directions is the standard reinforcement, though many contractors use 6x6 welded wire mesh (10 gauge) as a more economical alternative.

The choice between rebar and welded wire mesh depends on your driveway's specific conditions and expected loading. #4 rebar in an 18-inch grid pattern provides superior crack control and structural integrity, especially important in Ottawa's extreme freeze-thaw environment where concrete experiences over 50 freeze-thaw cycles annually. The rebar should be positioned at mid-depth of the concrete slab (approximately 75mm from the bottom in a 150mm thick slab) and supported on plastic chairs or concrete blocks to maintain proper placement during the pour.

Welded wire mesh (WWM 6x6-10x10) is more common for residential driveways because it's easier to handle and less expensive. The mesh should be pulled up into the concrete during placement, not left sitting on the base. Many contractors mistakenly leave the mesh at the bottom of the pour where it provides minimal benefit. When properly positioned at mid-depth, welded wire mesh provides adequate reinforcement for most Ottawa residential driveways with standard vehicle loading.

Ottawa's clay soils and deep frost conditions make reinforcement particularly critical. Clay subgrade expands and contracts with moisture changes, creating stress in the concrete slab above. The 1.2 to 1.5-metre frost depth means substantial ground movement during spring thaw. Proper reinforcement doesn't prevent cracking entirely, but it holds cracks tightly together, preventing them from opening wide enough to allow water penetration and freeze-thaw damage.

Concrete thickness matters as much as reinforcement in Ottawa. Residential driveways should be minimum 150mm (6 inches) thick, with 175mm recommended for heavier vehicles or RVs. The concrete mix should be minimum 30 MPa with air entrainment (5-8% air content) to resist freeze-thaw damage. Control joints should be cut every 3 metres in both directions to control where cracking occurs.

Fiber reinforcement is increasingly popular as a supplement to traditional rebar or mesh. Synthetic or steel fibers mixed into the concrete provide additional crack resistance and impact strength. Fiber reinforcement works particularly well in Ottawa's climate because it provides three-dimensional reinforcement throughout the slab thickness, not just at one level like rebar or mesh.

When to Hire a Pro: Concrete placement, reinforcement positioning, and finishing require professional expertise and equipment. The concrete must be placed, screeded, floated, and finished within a narrow time window, especially in Ottawa's variable weather. Control joints must be cut at the right time and depth, and proper curing is critical for achieving design strength before winter freeze-thaw exposure.

Find experienced concrete contractors through the Ottawa Construction Network who understand proper reinforcement placement and Ottawa's specific climate requirements for durable concrete driveways.