Do you need council approval for a retaining wall in SA?

Short answer: in South Australia, a retaining wall that holds back a difference in ground levels of one metre or less usually does not need development approval. Above that it does, and it will normally need an engineer's design. There are exceptions on both sides: some zones and council areas require approval for lower walls, tiered walls are measured on the total height, and a fence on top of the wall changes the rule. Work near the boundary can also mean you must give your neighbour formal notice.

These rules come from the Planning, Development and Infrastructure Act 2016 and its General Regulations, as summarised by the Legal Services Commission of South Australia in its Law Handbook chapter on retaining walls. Always confirm with your council before you build, because local rules differ.

The one metre rule, and its exceptions

• One metre or less: development approval is not usually needed if the wall retains a difference in ground levels of one metre or less.
• Zones and council areas: a wall of one metre or less may still need approval in a particular zone or council area, so ask your council.
• Tiered walls: it is the overall difference in ground levels that counts. Two walls of 70 cm stepped up a slope retain 1.4 m in total, so approval is needed.
• Fence on top: if the total height of wall plus fence is more than 2.1 m, measured from the lowest side of the wall, approval is needed.
• Part of a bigger build: where excavation or fill goes with a new building or other significant structure, the retaining wall details are usually included in that development application.

Councils also set out what they need to see. The City of Salisbury, for example, asks for a site plan, elevations showing materials and height, construction details and the engineer's design with footing calculations when a wall needs assessment (City of Salisbury, retaining walls). Its page treats walls of one metre or greater as needing an application, so check how your own council reads a wall that is right on the metre.

Building near the boundary: notice to your neighbour

Separate from approval, the Act requires notice where your work is treated as affecting the stability of the neighbouring land and access to that land may be needed. According to the Law Handbook, that includes:

• fill within 600 mm of the boundary, unless it is 200 mm or less high and for landscaping
• an excavation that cuts through a notional line sloping down at 1 vertical to 2 horizontal from a point 600 mm below natural ground level at the boundary

Notice is given on a Form 1 Initial Notice at least 20 business days before work starts. Skipping it can lead to a fine of up to $10,000. The neighbour can get an engineer's report on any shoring or underpinning needed, and the person doing the work generally pays for that report.

Who pays for the wall?

Land in its natural state needs no support. The general rule is that whoever changes the natural ground level, by filling or digging out, is responsible for retaining it. Where one neighbour fills and the other excavates, the cost is usually split in proportion. The Law Handbook gives the example of one side filling 300 mm and the other excavating 700 mm on a 1 metre wall: a 30 / 70 split. It is usually cheaper to agree on one shared wall than to build two, so talk to your neighbour early.

What affects the cost of a retaining wall

There is no honest per-metre price for a retaining wall without seeing the site, because two walls the same length can be very different jobs. The things that decide the price are:

• Height and length. Taller walls need bigger footings and more material per metre, and walls over the approval threshold add engineering and application costs.
• Material. We build concrete block walls and natural stone or boulder walls. Each suits different blocks, looks and budgets.
• Excavation and soil removal. Cutting into a slope means digging out and carting soil away.
• Drainage behind the wall. Water building up behind a wall is the most common reason walls lean and fail, so aggregate and drainage go behind every wall we build.
• Access. Whether machinery can reach the wall line, or everything goes in by hand.
• What goes with it. Building the wall, the paving in front and the garden above as one job usually saves rework.

Before any digging, check for underground pipes and cables through Before You Dig Australia, and check your Certificate of Title for easements: building over an easement generally needs approval from the authority that holds it.

How we handle approval on a quote

Every block is different. When we measure up, we will tell you straight up whether your wall is likely to need engineering or approval, and factor it into the quote. For walls in Gawler, Hewett, Evanston and the northern suburbs, see our retaining walls page. If the wall is part of a bigger backyard job, our landscaping in Gawler page shows how we tie walls, paving and gardens together. Or ask for a free quote.