Do I Need Gravel Under Concrete?

In many instances, the use of a gravel base under a concrete driveway is highly recommended, even in Auckland. The gravel base serves multiple purposes:

  • Drainage: Gravel allows water to drain away from the concrete slab, reducing the risk of water pooling under the concrete and causing damage over time. In Auckland’s climate, which is often rainy, this can be especially beneficial.
  • Stability and Load Distribution: A compacted gravel base can provide a stable, even surface for the concrete to rest on. It can also help distribute the load of the concrete and any vehicles or objects on the concrete, reducing the risk of cracking.
  • Prevent Soil Movement: Auckland’s geography includes areas of volcanic and clay soils, which can move or shrink/swell with changes in moisture. A gravel base can help protect the concrete slab from these movements.
  • Frost Protection: While Auckland’s climate does not typically include severe frosts, a gravel base can help insulate against any potential ground freezing in colder months, which could otherwise lead to ground heaving and subsequently damage the concrete slab.

However, the specific need for a gravel base, and the type and depth of gravel used, can depend on a number of factors:

  • Soil Type: The type of soil on your property can affect the need for a gravel base. For instance, if the soil is sandy and drains well, a gravel base might be less important for drainage but still beneficial for stability. See here for Auckland soil types.
  • Drainage Considerations: If the site has good natural drainage, that might reduce, but not eliminate, the need for a gravel layer for drainage purposes.
  • Load on the Driveway: If the concrete driveway is expected to bear heavy loads (e.g., large vehicles), a well-compacted gravel base will be important to help distribute these loads and protect the concrete.
  • Local Building Codes: Always check the local building codes or consult with a local professional. Auckland Council or your contractor may have specific requirements or recommendations for your driveway based on local conditions and standards.

The exact thickness of the gravel layer can vary but often ranges from around 100mm to 200mm for residential driveways. Compaction of the gravel is also crucial to provide a stable base.

Remember to always consult with a local professional or our Auckland concreting contractors when planning your concrete driveway. They can provide advice tailored to your specific circumstances and ensure that the work meets all local standards and requirements.

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