Retaining walls

If you’re planning to construct retaining walls on your property, development approval is required if:

  • the retaining wall retains a difference in ground level exceeding 1m; or
  • two retaining walls or a series of retaining walls are used together in a tiered fashion to retain an overall difference in ground level exceeding 1m; or
  • the total height of a retaining wall with a fence above exceeds 2.1m (measured to the lowest side).
  • the property is a State or Local Heritage Place
  • the property is in a Hills Face Zone, Designated Subzone, Flood Zone or Overlay delineated by the Planning & Design Code.

Tiered retaining walls

A common alternative to constructing one large retaining wall, is to construct a series of shorter walls to terrace the land. In this instance, it is recommended that the distance between walls is to be twice their height to form a slope of 1 in 2 (i.e. a 1m wall should be built every 2m).

Consequently, if the walls are less than 1m in height then development approval is not required.

Alternatively, if the spacing between walls are closer together, the surcharge loads imposed by the higher wall on the wall below may need to be considered in the structural design.

The height of the wall will be considered from the bottom of the lower wall to the top of the higher-level wall, and if the total height is over 1m. In this instance, lodging a development application on PlanSA is required.

Who is responsible for stabilising the land and associated costs?

It is important to note that if the owner of a property proceeds to alter the natural lay of the land, they are also responsible in stabilising the site by creating an appropriate landscaped batter or by providing a retaining wall.

However, where both property owners agree to alter land along a shared boundary, they would be jointly responsible.

The apportioning of responsibility and cost is a matter between the affected parties which may require legal opinion to decipher and determine. It is important to note that council does not have powers to determine who pays costs associated with fencing and retaining walls.

If you and your neighbour are unable to agree on sharing of costs, find out more or seek advice from the Legal Services Commission of SA.

Fences located on retaining walls

If a fence is proposed to be located on top of a retaining wall, development approval is required to be obtained if the total height (measured from the lowest level of the retaining wall to the highest point of the fence) exceeds 2.1m. Likewise, in the case of a brick or masonry fence located on the top of a retaining wall if the total height exceeds 1m.

Types of retaining walls

Moss rock/ dry stone/ modular block retaining walls: generally limited to a maximum height of 2m and will require an engineer to certify the suitability of the location and design proposed (not recommended in shared boundary circumstances).

Reinforced stone retaining walls: require substantial anchorage at the base of the wall, usually embedded 300mm into the natural ground to reduce slippage. The slope of the wall repose distance from base to top from vertical is an important part of the construction, typically a ratio of 4:1 (for a 2m high wall the distance of repose needs to be at least half a metre).

Concrete sleeper/ hot rolled steel section configured retaining wall: is a popular choice due to its ease of construction and cost effectiveness. Vertical steel sections are placed into suitable concrete filled piers at spacings to suit the concrete sleeper length.

Drainage of retaining walls

When considering different walling types, the outcome will largely be dependent on establishing an adequate free drainage system. Many retaining walls fail either due to the use of inappropriate of construction materials or the build-up of surface drainage water behind the constructed walls resulting in hydrostatic pressure destabilising the wall.

An agricultural pipe (AG Pipe) is commonly used at the base of retaining walls to disperse water build up. Please note, it is good practice to connect both ends of the AG pipe to a stormwater system to prevent any excess water flowing onto any neighbouring properties.

Further information

Legal Services Commission SA | Retaining walls

PlanSA | Why you need approval

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