Retaining Walls in South Australia: Engineering, Approvals, and Legal Responsibilities Explained

Retaining walls are a common feature in residential and commercial developments across South Australia, particularly on sloping or subdivided land. While they are often treated as simple landscaping elements, retaining walls are structural systems governed by specific planning, engineering, and legal requirements.

This article explains when retaining walls require approval, how neighbouring properties are affected, who is responsible for construction and maintenance, and why professional engineering input is critical for compliance and risk management.

What Is a Retaining Wall (and Why It Matters)?

A retaining wall is a structure built to retain a difference in ground levels. While a retaining wall may support a fence, it is not legally considered a fence and is regulated under different laws and standards. In South Australia, retaining walls are primarily governed by:

• Common law principles of nuisance
• The Planning, Development and Infrastructure Act 2016 (SA)
• The Planning, Development and Infrastructure (General) Regulations 2017 (SA)

Because retaining walls affect land stability, drainage, and neighbouring properties, they carry both structural and legal risk if not designed and constructed correctly.

Do Retaining Walls Require Development Approval?

In South Australia, development approval is often required where a retaining wall is associated with excavation or fill.

Key approval principles include:

• Retaining walls associated with building works usually require approval as part of the development application.
• Retaining walls constructed for landscaping, repair, alteration, or demolition may still require approval, depending on location and extent.
• Retaining walls that retain one metre or less of ground level difference do not usually require approval, but exceptions apply based on zoning or council policy.
• Tiered retaining walls are assessed on the total retained height, not individual wall heights.
• Where a fence is installed on top of a retaining wall, approval is required if the combined height exceeds 2.1 metres (measured from the lower side).

Because requirements vary between councils, confirmation with the local authority is essential before construction proceeds.

When Must Neighbours Be Notified?

Notice to adjoining landowners is mandatory where retaining wall works affect the stability of neighbouring land.

Works that are treated as affecting stability include:

• Fill placed within 600 mm of a boundary beyond minor landscaping limits
• Excavation that intersects a notional plane extending downwards at a slope of 1 vertical to 2 horizontal from a point 600 mm below natural ground level at the boundary

In these cases, the owner proposing the work must:

• Provide at least 20 business days’ notice
• Use the prescribed Form 1 – Initial Notice to Owner of Affected Site
• Include sufficient detail about the proposed works and duration

Failure to give notice can result in enforcement action and fines of up to $10,000

Who Is Responsible for Building a Retaining Wall?

Responsibility for retaining walls is tied to who altered the natural ground level.

General principles include:

• Land in its natural state requires no support
• The party who fills or excavates land is responsible for retaining the altered ground
• Where both neighbours alter land, responsibility is apportioned according to the extent of fill or excavation

In many cases, a single retaining wall benefiting both properties is more practical, but this requires agreement between neighbours.

How Are Costs Apportioned?

Where both parties contribute to the need for a retaining wall, costs are typically apportioned based on benefit. For example:

• If one property fills 300 mm and the adjoining property excavates 700 mm, costs may be split 30% / 70%
• Where both parties benefit equally, costs may be shared 50/50

Disputes over cost apportionment are resolved through negotiation or the courts, not by local councils

Existing Retaining Walls and New Works

Where an existing retaining wall is present:

• A party proposing new fill must ensure the existing wall is not overloaded
• A party proposing excavation may need to construct additional retaining or underpinning
• Engineering assessment is often required to confirm whether the existing wall can accommodate the new conditions

This is a common trigger for engineering involvement on infill and subdivision projects.

Maintenance Responsibilities and Repairs

Responsibility for maintaining a retaining wall generally follows who benefits from it:

• Where both properties benefit, maintenance costs may be shared proportionally
• Where only one property benefits, that owner is responsible for maintenance

Repairs may require development approval, particularly where stability is affected or materials change. Minor repairs using similar materials may be exempt, but confirmation with council is recommended

Why Engineering Input Is Critical

Retaining walls are structural systems with legal consequences. Professional engineering input ensures:

• Compliance with AS 4678 and the NCC
• Adequate stability, drainage, and durability
• Reduced risk of neighbour disputes and enforcement action
• Protection against costly rectification or legal exposure

For builders and property owners, engaging a qualified retaining wall engineer is not an added cost it is a risk-control measure.

FAQ

Legal Disclaimer

Important Notice

This article is provided for general information purposes only. It does not constitute legal advice, engineering advice, or a substitute for professional consultation.

Retaining wall requirements in South Australia depend on site-specific conditions, planning controls, and individual circumstances. Laws, regulations, and council policies may change over time, and their application can vary between locations.

Before commencing any retaining wall works, you should:

• Obtain site-specific advice from a qualified structural or civil engineer, and
• Seek independent advice from a qualified legal practitioner regarding your legal rights, responsibilities, and obligations.

OB Engineering Group does not accept liability for reliance on the information contained in this article without appropriate professional advice.