In many cases, yes — road base can be used instead of AP40 under a DIY driveway, but the two materials are not always interchangeable. The right choice depends on your soil conditions, the driveway surface you're laying, and what's locally available in your region. Understanding the difference before you order your materials can save you a costly redo.
What Is AP40 and What Is Road Base?
AP40 (Aggregate Pavement, 40 mm maximum particle size) is a well-graded crushed rock blend containing particles ranging from 40 mm down to fine dust. The grading is engineered so the material compacts tightly, locks together, and provides a stable, load-bearing layer. It is specified in many NZ pavement design guides and is widely used under concrete and asphalt driveways.
Road base is a broader, informal term used across NZ for compactable crushed rock sub-base material. Depending on your supplier and region, road base may be virtually identical to AP40, or it could be a slightly different grading — sometimes called AP65, AP20, or crusher run. Always ask your quarry or landscape supplier for the specific grading specification of what they're selling as "road base."
Key Differences to Know
| Property | AP40 | Generic Road Base |
|---|---|---|
| Max particle size | 40 mm | Varies (20–65 mm typical) |
| Grading standard | Well-defined NZ spec | May vary by supplier |
| Compaction performance | Excellent | Good to excellent (spec-dependent) |
| Availability | Most NZ regions | Widely available |
| Typical use | Under concrete, asphalt, pavers | Sub-base, fill, unsealed roads |
When Road Base Works Fine
If your local supplier's road base is a well-graded crushed rock blend with a similar particle size range to AP40, it will generally perform just as well for a residential driveway sub-base. This is common in many parts of NZ where quarries sell road base to an equivalent standard under a different name.
Road base is often a practical choice when:
- You're laying a gravel or chip-seal driveway where tolerances are more forgiving.
- Your ground conditions are stable — firm, free-draining soils like gravel or compacted clay.
- Your supplier can confirm the material is well-graded crushed rock that compacts to a solid, stable layer.
- The driveway has light to moderate vehicle loads (standard passenger cars and occasional light trucks).
When AP40 Is the Better Choice
For more demanding applications, specifying AP40 (or asking your supplier to match that grading) gives you greater confidence in the result:
- Under concrete or asphalt — these surfaces need a consistent, well-compacted sub-base to prevent cracking and settlement. A poorly graded sub-base is one of the most common causes of driveway failure.
- Soft or wet ground — expansive clays or poorly drained soils common in parts of the Waikato, Northland, and South Island benefit from a properly engineered sub-base depth and grading.
- Heavy vehicle access — if tradesperson vans, delivery trucks, or a boat trailer will regularly use the driveway, a correctly specified sub-base matters more.
- Steep driveways — poor compaction on a slope can lead to washout and erosion over time.
How Deep Should Your Sub-Base Be?
As a general guide for a residential driveway:
- Stable, free-draining ground: 100–150 mm of compacted sub-base is often sufficient.
- Soft or clay soils: 150–200 mm or more may be needed, sometimes with a geotextile fabric underneath to prevent sub-grade contamination.
Always compact in layers no deeper than 100–150 mm using a plate compactor (available to hire from most tool hire shops). Tipping the full depth in one go and compacting the top is a common DIY mistake that leads to soft spots later.
Do You Need a Building Consent?
Most residential driveways do not require a building consent under Schedule 1 of the Building Act 2004, but there are exceptions — for example, if the driveway involves significant earthworks, retaining walls over certain heights, or connections to a public road that require council approval. Always check with your local council before starting work, as rules vary by territorial authority. You may also need a vehicle crossing permit from your council for the kerb cut.
For guidance on the NZ Building Code and consent requirements, MBIE Building Performance is a reliable starting point.
Sourcing Materials in NZ
You can source AP40 and road base from local quarries, landscape suppliers, and building merchants. Stores like Mitre 10, Bunnings, and PlaceMakers stock bagged and bulk aggregates, though for larger driveway projects a direct quarry delivery is usually more economical. Always ask for the grading specification in writing so you know exactly what you're getting.
When to Call a Professional
If your ground is soft, waterlogged, or made up of expansive clay, it's worth getting a driveway layer or civil contractor to assess the sub-grade before you start. Getting the sub-base wrong is expensive to fix after the fact — especially under concrete or asphalt. A professional can also advise on drainage, which is critical for driveway longevity in NZ's wet climate.
For technical guidance on pavement materials and performance, BRANZ publishes research relevant to NZ construction conditions.
You can find qualified, local driveway layers and civil contractors on tradedirectory.co.nz to get a quote or a second opinion before you commit to materials.
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