How Thick Should a Concrete Driveway Be? (Australian Standards Explained)

Concrete driveway thickness is one of those details most Adelaide homeowners never think about until the concrete fails — and by then it's too late to fix without ripping it all up.

The good news: Australian Standards give us clear minimum requirements, and understanding them takes 5 minutes. Here is what you need to know before your concreters arrive on site.

The Australian Standard Minimum: 100 mm

For residential concrete driveways in Australia, the baseline minimum thickness is 100 mm (10 cm), as recommended under AS 3600 (Concrete Structures) and widely adopted across the residential building industry.

At 100 mm with SL72 reinforcement mesh, a standard residential driveway can handle:

• Passenger vehicles (up to 3 tonnes)
• 4WDs and SUVs
• Light trailers and camper vans

This is the standard we use at Opal SA Construction for all residential driveways unless the site or application demands more.

When You Need More Than 100 mm

Some situations call for a thicker pour:

Application	Recommended Thickness	Reason
Standard residential driveway	100 mm	Passenger vehicles only
Driveway with trailer access	125 mm	Frequent heavier loads
Concrete in front of garage (turning area)	125 mm	Point loads from reversing
Driveway accessed by trucks (removalist, concrete)	150 mm	Heavy vehicle axle loads
Class H1/H2 reactive clay soils (northern/southern Adelaide)	100–125 mm + deeper roadbase	Soil movement resistance
Commercial car park (light vehicles)	125–150 mm	Continuous traffic

The Role of Reinforcement

Thickness alone is not enough. What's underneath — and inside — the concrete matters equally:

Reinforcement mesh:

• SL72 mesh (7.1 mm bar, 200 mm centres) — standard for passenger vehicles
• SL82 mesh (8.9 mm bar, 200 mm centres) — recommended for reactive clay sites in Adelaide's north and south

Compacted roadbase:

• Minimum 100 mm DGB20 (compacted) under every residential slab
• 150 mm on Class H1/H2 soil sites (Salisbury, Gawler, Morphett Vale)
• Compaction tested to 95% standard proctor density — poorly compacted roadbase causes slab cracking regardless of concrete thickness

Moisture barrier:

• 0.2 mm polyethylene sheet between roadbase and concrete on all slab-on-ground work
• Prevents moisture migration from subsoil into the slab (critical in Adelaide's reactive clays)

Adelaide Soil Conditions and What They Mean for Thickness

Adelaide's soil reactivity directly affects what thickness and reinforcement your driveway needs:

Zone	Suburbs	AS 2870 Class	Recommended Thickness
Coastal / inner west	Glenelg, Henley Beach, Port Adelaide	Class A/S	100 mm standard
Inner eastern	Norwood, Unley, Campbelltown	Class M	100 mm standard
Northern corridor	Salisbury, Elizabeth, Para Hills, Gawler	Class H1–H2	100–125 mm + deeper base
Southern corridor	Morphett Vale, Reynella, Hallett Cove	Class H1	100–125 mm
Hills fringe	Mitcham, Blackwood, Burnside	Class E	Engineer assessment

Before we quote any job in Adelaide, we check the AS 2870 soil classification for the suburb. If you are in a H-class or E-class area, we factor that into the slab design.

How Concrete Thickness Affects Cost

Adding 25 mm to a 30 m² driveway adds roughly 0.75 cubic metres of concrete — about $150–$200 in materials. Included in the installed price, the difference between 100 mm and 125 mm for a standard driveway is typically $3–$5 per m².

That is a small premium that can prevent thousands of dollars in repairs in a reactive clay zone.

The Difference Between Depth and the Overall Slab Build-Up

When concreters talk about "100 mm concrete", they mean the concrete layer only. The total excavation depth is deeper:

Layer	Typical depth
Concrete	100 mm
Compacted roadbase	100–150 mm
Excavation for reactive clay sites	Extra 50–100 mm
Total excavation from finished surface	200–350 mm

This is why quotes vary — what looks like "just pouring concrete" actually involves significant earthworks, base preparation, and compaction before the concrete goes down.

Questions to Ask Your Concreter

Before you sign a quote, confirm:

What thickness is your quote based on? (Should be at least 100 mm)

What reinforcement mesh are you using? (SL72 minimum; SL82 on reactive clay)

How deep is the roadbase? (100 mm minimum compacted DGB20)

Are you including a moisture barrier? (Required on slab-on-ground in SA)

How do you handle the soil conditions in this suburb?

If a concreter cannot answer these questions specifically, they may be cutting corners on the slab specification.

Summary

• 100 mm is the minimum for residential driveways in Australia
• 125 mm is recommended for trailer access, reactive clay zones, or turning areas
• Reinforcement and roadbase compaction matter as much as thickness
• Adelaide's H-class soils in the north and south need extra care
• The cost difference is $3–$5/m² — worth paying on reactive clay sites

For a free on-site assessment of your site's soil conditions and the right slab specification for your suburb, call Javed on 0466 801 058 or request a free written quote.

Internal links to include:

• Concrete Driveways Adelaide
• Concrete Slabs Adelaide
• Residential Concreting Adelaide
• How Much Does a Concrete Driveway Cost in Adelaide?