Retaining walls look simple. A few sleepers, some posts, job done. But they're one of the most commonly under-engineered structures on Australian residential blocks — and one of the most common sources of council enforcement, neighbour disputes and expensive rebuilds.
The rules also differ significantly between states. A wall that's perfectly fine without approval in Brisbane would need council sign-off in Sydney. Here's how it actually works.
Three things determine whether you need approval:
Height gets all the attention, but the second and third points catch out just as many people.
In Queensland, retaining wall requirements sit under the Building Act 1975 and the Queensland Development Code. As a general guide:
| Retained height | What's typically required |
|---|---|
| Under 1 m | Usually exempt from building approval on standard residential sites. |
| 1 m – 1.5 m | Building approval, typically via a private certifier. |
| Over 1.5 m | Building approval plus a structural certificate from an RPEQ. |
The under-1 m exemption isn't automatic. It generally applies only where there's no surcharge loading, the wall is a reasonable distance from buildings, it isn't part of a pool barrier, and the site isn't heritage or otherwise constrained.
Where certification is required, the design is certified by an RPEQ via a Form 15. (See our guide to [Form 15 vs Form 16].)
NSW is considerably more conservative, and this catches out plenty of people who've read Queensland advice online. Retaining walls are generally assessed under the State Environmental Planning Policy (Exempt and Complying Development Codes) 2008:
| Retained height | What's typically required |
|---|---|
| Up to ~600 mm | May qualify as exempt development, if setback and other criteria are met. |
| ~600 mm – 1 m | May qualify as Complying Development (CDC) via a private certifier. |
| Over 1 m | Typically a CDC or Development Application (DA), with structural engineering certification. |
So in NSW, an 800 mm wall — modest by most standards — usually steps outside exempt development.
Critically, your council's Local Environmental Plan (LEP) and Development Control Plan (DCP) can impose stricter requirements than the state code. Some councils set thresholds lower again. Always check your specific council.
(Rules in Victoria and the ACT differ again — building permits are generally issued through a registered building surveyor, with engineering required above modest heights. Confirm with your surveyor or certifier.)
This trips up more people than any other point.
Approval thresholds are generally based on retained height — the difference in ground level from one side of the wall to the other — not the total height of the wall you can see.
If your wall is built with 300 mm sitting below finished ground and 900 mm of soil retained above, the number that matters is the 900 mm of retained ground, not the total block height. Measure what the wall is holding back.
Even a low wall can require approval and engineering if any of these apply:
Surcharge loading. This is the big one. If anything sits on or near the soil the wall is retaining — a driveway, a parked car, a pool, a shed, a deck, or another building — the wall carries far more load than height alone suggests. Surcharge generally removes any height exemption, regardless of how low the wall is.
Proximity to a boundary, easement or drainage line. Building close to a boundary can affect a neighbour's land and often triggers approval. Easements and drainage lines have their own restrictions.
Overlays. Flood, bushfire, landslip, heritage and environmental overlays can all add requirements.
Pool barriers. Walls forming part of a pool barrier must satisfy pool safety rules regardless of height.
Tiered or terraced walls. Two 800 mm walls stacked close together can behave structurally as one taller wall. Councils and engineers often assess them as a combined system rather than two independent walls.
Legally, above the thresholds set out above. Practically, an engineer is worth engaging well before that, particularly where:
An engineer designs for the things you can't see: lateral soil pressure, drainage and water pressure behind the wall, footing depth and post embedment, global stability (whether the whole soil mass could slip), and appropriate materials for the loads involved.
Failures are rarely about the sleepers or blocks themselves. In practice, the recurring causes are:
Drainage. Water building up behind a wall creates enormous hydrostatic pressure — routinely the single biggest cause of failure. Aggregate drainage, geofabric and an outlet aren't optional extras.
Unaccounted surcharge. A wall designed for soil alone, then a driveway or shed built above it.
Inadequate embedment. Posts or footings not deep enough for the retained height.
No engineering at all. Product spec sheets are based on assumptions about your site that may not hold.
A failed retaining wall is expensive — you're paying for demolition, re-excavation, engineering and rebuild, and possibly repairing whatever it damaged on the way down.
It's not a paperwork technicality. Building without required approval can mean council enforcement and orders to modify or remove the wall, difficulties at sale when a conveyancer finds unapproved structures, insurance complications if the wall fails or causes damage, and liability exposure if a neighbour's land or property is affected.
Retrospective approval is sometimes possible, but it's almost always more expensive and more painful than doing it properly first.
QED Engineers designs and certifies retaining walls across [QLD, NSW, VIC & ACT] — from single residential walls to tiered and surcharge-loaded structures — with the documentation your certifier or council needs. In Queensland we provide RPEQ-certified Form 15 design certification.
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This article is general information only. Approval thresholds vary between states and between local councils, and are subject to change. Always confirm requirements for your specific site with your local council or a private building certifier before starting work.
How high can a retaining wall be without council approval? It depends on your state and council. In Queensland the general threshold is around 1 m of retained height; in NSW it's much lower, around 600 mm. Both assume no surcharge loading and adequate setbacks — and individual councils can be stricter, so confirm locally.
Does a retaining wall under 1 m need an engineer in Queensland? Not always for approval purposes, but engineering is strongly recommended if there's any surcharge (driveway, vehicle, pool, structure), if the site slopes, or if soils and drainage are poor. Over 1.5 m, an RPEQ structural certificate is required.
What is retained height? The difference in ground level between the high side and low side of the wall — essentially how much ground it's holding back. Approval thresholds are generally based on this, not the total visible height of the wall.
Does a driveway above my wall change things? Yes, significantly. A driveway or parked vehicle is surcharge loading, which increases the forces on the wall substantially and generally removes any height-based exemption.
Do I need approval for a wall on the boundary? Usually yes, or at minimum additional scrutiny. Walls on or near boundaries affect adjoining land, and many councils require approval regardless of height. Talk to your neighbour early too — boundary retaining walls are a common source of disputes.
Can I build two shorter walls instead of one tall one? Sometimes, but not as a way around approval. Tiered walls built close together can act structurally as a single taller wall, and are often assessed that way. Have the arrangement designed properly rather than assumed.
