It's one of the first questions people ask at the counter: do I need council approval for this wall? For a lot of garden walls the answer is no. For some it's a firm yes, and finding out after the wall is built is an expensive way to learn. Here's how it works in South Australia, in plain terms.
The short answer
In South Australia, a retaining wall needs development approval and engineering if any of these apply:
- it retains more than 1.0 m of soil,
- it sits under a surcharge, such as a fence, a driveway or a building, or
- it has a fence on top that takes the combined height over 2.1 m, measured from the low side.
If none of those apply, your wall is likely to be minor work. Your local council is the one that confirms it, so check with them before you start. The rules are set under the state's planning system, and the PlanSA website is the place to read them in full.
What the terms mean
Retained height is the height of soil the wall holds back, measured from the ground on the low side to the ground on the high side. It isn't the height of the sleepers you can see, and it isn't the length of the posts. A wall with five 200 mm sleepers above ground might retain a metre of soil, or a lot less if the ground behind it slopes away.
Surcharge is any extra load near the top of the wall. A fence, a car on a driveway, a shed slab or the wall of a house all push down on the soil behind the wall, and the wall has to hold that back too. That's why a low wall under a driveway can need engineering when a taller wall around a garden bed doesn't.
Combined height is the retaining wall plus any fence on top of it, measured from the low side. A 900 mm wall with a 1.8 m Colorbond fence on top is 2.7 m from the neighbour's side, and that's over the 2.1 m line.
Boundary walls need extra care
A wall on a boundary usually has a fence on top, and that's where the surcharge and combined-height rules come in. If your wall is on or near a boundary, talk to your neighbour early and check with council about the fence and the wall together, not one at a time.
What engineering involves
Retaining walls are designed to the Australian Standard AS 4678. An engineer looks at your soil, the drainage, the footing and anything sitting on or behind the wall, and specifies:
- the sleeper thickness and length,
- the steel post section and its length,
- how deep the post goes in the ground and the size of the footing, and
- the drainage behind the wall.
The design is specific to your site, so a wall that's fine at a mate's place isn't automatically fine at yours.
Where we fit in, and where we don't
We supply the materials. We don't design or certify walls, and we don't give engineering advice. If you need an engineer, we can put you in touch with an independent structural engineer. You engage them directly and they set their own fees.
Once you have the drawings, send them through with your quote request and we'll price every item from them, line by line, so you can match each line on our quote to the engineer's specification.
One thing worth knowing: seconds can't go in an engineered wall. Seconds are graded-out sleepers with no engineering duty rating, so any wall that's engineered, certified or specified by an engineer, certifier, council or head contractor needs first-grade sleepers. Our post on seconds covers the details.
What about the wall builder?
The wall builder on this site gives you an indicative materials estimate from the wall length and height. It's handy for a budget and a first quote. It isn't an engineering design, and it doesn't replace one where your wall needs approval.
Before you dig
- Measure the retained height from the low side, at the highest point of the wall.
- Note anything near the top of the wall: fence, driveway, slab, pool, building.
- Check where the boundary is, and talk to the neighbour if the wall is on it.
- Call your council if you're anywhere near 1.0 m retained or 2.1 m combined.
- Lodge a free Before You Dig Australia enquiry at byda.com.au before any excavation.
Got a wall in mind?
Send us the length, the retained height, the delivery suburb and any drawings you have, and we'll get a metro quote back to you within 24 hours. Call 0439 361 734, email sales@fenceplinths.com.au, or come in to the yard at Virginia and have a chat.
Cheers,
Alex and the team
This post is general information about how approval works in South Australia, not advice about your wall. Your council and your engineer have the final say.