The answer usually depends on the wall's height, any weight sitting on the ground behind it, and its distance from buildings and other walls. A short wall edging a garden bed can be accepted development with no building approval required. Run a driveway across the top of the same wall and things change completely, because the cars above add forces the wall must be designed to carry.
Queensland regulates building work through the Building Act 1975 and the Building Regulation 2021. Building certifiers, most of them private, assess and approve work that needs building approval, while the Cairns Regional Council planning scheme operates as a separate set of rules. Builders taking on work above a set value also need a QBCC licence. These rules carry conditions and are revised periodically, so treat this article as general guidance for judging if approval will probably apply to your project. For a definite answer about your wall, ask a building certifier or Cairns Regional Council.
Signs your wall will probably need approval
Expect to involve a certifier and an engineer, and possibly to need building approval, if any of these apply.
- Wall and retained soil together exceed one metre: the measurement is taken from natural ground at the wall, so a wall can be taller on paper than it appears.
- Weight sits above it: a driveway, house, pool, carport or a slope that continues climbing.
- Less than 1.5 metres from a building or another retaining wall, or forming part of a pool barrier.
- The land carries a planning scheme overlay, for example hillslopes, landslide hazard, flooding or acid sulfate soils, or the wall would send stormwater onto a neighbour's property.
Because these conditions overlap, a wall that seems clearly exempt can turn out not to be. Stepped terraces are a frequent example: two low walls built less than 1.5 metres apart fail the clearance condition no matter how short each one is.
Walls that may not need building approval
The Schedule 1 exemption is aimed at small, straightforward walls.
- One metre or less of wall plus retained soil, holding back garden soil only, with no load inside the zone of influence.
- 1.5 metres or more from any building or other retaining wall, and not part of a pool barrier.
- Consistent with the planning scheme: exempt building work may still have to satisfy Cairns Regional Council planning rules, especially on land with an overlay.
An exempt wall still has to be built well. Exemption just means no one will inspect it, which makes good workmanship more important, not less.
Surcharge, explained
Surcharge confuses more owners than any other term, and it is what most often turns a simple job into an engineered one.
It refers to any weight on the ground behind the wall beyond the soil. Driveways are the usual culprit around Cairns, since many hillside homes in suburbs such as Bayview Heights, Brinsmead, Redlynch, Edge Hill and Whitfield sit on benched blocks with the drive cut along the slope above a wall. Cars and utes are heavy and constantly moving, and their weight pushes into the soil the wall is holding back. A wall carrying surcharge generally calls for an engineer's design to AS 4678, and our retaining walls team builds to that design.
A rough guide by situation
Use the table for an initial read, then check the details with a building certifier or Cairns Regional Council.
| Situation | Approval likely? |
|---|---|
| Wall and retained soil more than about 1m high | Likely, with an engineer and a building certifier |
| Any height, with a driveway, building or rising slope above | Likely, with an engineer and a building certifier |
| Closer than 1.5m to a building or another wall, or part of a pool barrier | Likely; ask a certifier |
| Land affected by a planning scheme overlay | Possibly; ask Cairns Regional Council |
| Included in a larger project that already holds building approval | Possibly covered; check with your certifier |
| 1m or under, garden soil only, no surcharge, 1.5m from buildings and walls | Generally accepted development; double-check each condition |
The cost of going without approval
The fallout usually comes years later, which is exactly why cutting the corner is tempting and a poor idea. An unapproved wall may be picked up by a building and pest inspector or a buyer's conveyancer, retrospective approval can require exposing finished work, and council can issue a notice to have it put right. None of that is something you want to sort out while a settlement date is looming.
Drainage matters, approved or not
Whatever the approval position, take this point away. Most retaining walls that fail do so because of water, and a Cairns wet season, especially over clay, will find any weakness.
Building it to last, and how we help
Waterlogged soil is much heavier than dry soil and presses on the wall with hydrostatic pressure it was never meant to take. Without a way out, that pressure keeps rising until the wall bows, cracks or tilts, and tropical downpours can saturate the ground in a matter of hours. Weep holes, a slotted drain pipe along the footing, geotextile fabric and clean free-draining gravel behind the wall prevent it, and they cost little next to rebuilding. We include them on every wall, inspected or not, and we coordinate with the project engineer and certifier when approval is required. Our excavation crew also requests buried service locations from Before You Dig Australia ahead of any digging.