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How Thick Should a Concrete Driveway Be? A Waiheke Guide

22 July 2026 · 5 min read

Key Takeaways

  • 100mm is the usual domestic minimum; 125 to 150mm where heavier vehicles, trailers or delivery trucks use the drive.
  • Thickness alone proves nothing. A thick slab on an uncompacted base still fails — depth and groundwork work together.
  • Reinforcement has to sit inside the slab, chaired to height. Mesh lying on the base contributes essentially nothing.
  • Edges and entry points need more, because that is where support is weakest and loading is highest.

One hundred millimetres is the normal minimum for a domestic driveway, rising to one hundred and twenty-five or one hundred and fifty where heavier vehicles are involved. But thickness on its own is close to meaningless. A thick slab on badly prepared ground fails the same way a thin one does, and on Waiheke the ground is usually the harder problem.

Below is what the figures should be, why the base matters at least as much, and the two places where extra depth genuinely earns its keep.

What thickness is actually doing

Thickness governs how well a slab spreads load and how much it resists bending. Too thin for the traffic and it flexes, and concrete does not tolerate being flexed — it cracks. The load has to travel down through the slab into the base and then into the ground, and every one of those layers has to be up to the job.

The figures worth working to

Which is why the question is never just how thick, but how thick over what.

UseThicknessReinforcement
Cars only, normal ground100mmStandard mesh, chaired into the slab
Campervans, trailers, occasional truck125 to 150mmHeavier mesh or bar; deeper base
Shared or commercial access150mm and aboveEngineered design, heavier steel, planned joints

These are working figures for normal ground. Soft, filled or reactive ground pushes each of them upward.

Why the base matters at least as much

If you regularly park a trailered boat, or a delivery vehicle comes up your drive, tell whoever is quoting. It changes the specification, and it is far cheaper to build for it than to repair a slab that was not.

Where the steel has to sit

This is the part that gets skipped when a price looks too good. Concrete sitting on topsoil, vegetation or fill that was tipped in and never compacted will lose support as that material consolidates, and the slab cracks under its own weight regardless of how deep it is.

The two places that need extra

Proper preparation means digging out unsuitable material to a depth that suits what is actually there, then laying and compacting base course in layers rather than in one deep lift. On reactive clay it often means going deeper than people expect, and it always means giving water somewhere to go.

What to ask whoever is quoting

Reinforcement holds the slab together across any crack that forms, so the two sides cannot move independently. It only does that if it is in the right place.

FAQ

Frequently Asked Questions

For a standard domestic drive carrying cars, on well-prepared ground, one hundred millimetres with correctly positioned mesh is the usual specification and it performs well. It stops being enough once heavier vehicles enter the picture — a trailered boat, a caravan, a delivery truck or a works vehicle. It is also marginal on soft or reactive ground, where the slab has to bridge more. The honest answer comes from the ground and the traffic, not from a default.

Not by itself, and this is the most common misconception. A one hundred and fifty millimetre slab poured onto topsoil or a base compacted in one deep lift will crack and settle just like a thin one, because the failure is loss of support rather than lack of depth. Thickness and base preparation work together. If you only had budget for one, spending it on excavation and compaction generally buys more durability than adding twenty-five millimetres of concrete.

Inside the slab, chaired up so it sits around the middle to upper third depending on the design — not on the base. This matters enormously and it is frequently got wrong. Reinforcement resists tension, and in a ground-bearing slab the tension is not at the very bottom. Mesh lying on the sub-base is effectively buried metal doing nothing. On a coastal site it also needs adequate concrete cover above it so salt cannot reach the steel.

Yes, and it is a detail worth insisting on. The edge of a slab has ground on one side only, so it has less support than the middle, and it is precisely where vehicle wheels run when turning in and out. Thickening the perimeter, often with additional steel through it, stops the edge breaking away. The same applies at the entry point from the road, where every vehicle passes and frequently turns under load.

Yes, and their answer tells you a lot. A contractor who quotes the same thickness regardless of what is underneath has not assessed the ground. You should expect them to talk about soil conditions, how much excavation they intend, base course depth, what vehicles will use it, and where extra reinforcement is going. If those subjects do not come up before a price is given, the price is a guess.

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