Go ahead - but properly

Retaining walls less than 1.5m high do not need a building consent, but still need to be constructed to building code standards.

That is because even low walls can be subjected to loads which threaten their stability. Those loads vary with the type of ground and the soil's water content.

The code lays out construction methods for various wall types and materials.

A Building Research Association (Branz) bulletin which details the code's requirements emphasises the need for drainage behind the wall to prevent water build-up - at least 300mm thickness of gravel for the full height of the wall and a drain at the bottom discharging into a silt trap approved by the local council.

Branz says it would be sensible to provide a barrier, such as a fence, at the top of the retaining wall where there is a path below or where people might gather - although the code requires a safety barrier on a domestic retaining wall only if it is one metre or higher and adjacent to an access path to the house.