How high can a retaining wall be without approval?

Only as high as the line your state or council draws, and that line comes down once the wall has work to do. A low garden wall holding back soil in open ground can often go ahead without building approval. Put a driveway, a building or a pool above it, build it near a boundary or stand a fence on top, and it often needs approval and an engineer’s design even at a modest height. The height is read where the wall stands tallest.

What decides it?

Height is the obvious test, measured from the ground in front of the wall to the top of the soil it holds back. The load behind the wall is the one people miss. Soil on its own presses on a wall, and a car, a slab, a footing or a slope above presses harder, which is why a wall that carries anything is designed by an engineer even where a plain garden wall of the same height would not be.

Where the wall sits counts as much. Near a boundary, a failure lands on the neighbour’s land, so the wall brings assessment and often a talk over the fence first. A wall over a sewer main or an easement needs the asset owner’s consent first, the water draining through it has to go somewhere the council accepts, and in a landslide or flood overlay the council can ask about the cut and the fill as well as the wall. The post on building near a sewer main covers that consent.

Does a fence on top change it?

Yes. A fence on a retaining wall adds its own height and the wind it catches, and from the low side the wall and the fence read as one structure. A wall and a fence that would each pass alone can need approval together. The post on fences on retaining walls explains how the heights are read together.

Who decides?

The certifier, or the council where it assesses building work, decides whether the wall needs building approval, and an engineer designs it once it passes the height or the load where a design is needed. The council decides any planning question an overlay brings, and the asset owner decides anything over its main.

What goes on the site plan?

the wall’s run at its true length, with the height of each section
the distance from the wall face to the boundary
what sits above the wall and loads it, such as a driveway, a slab or a pool
the existing levels, so the cut side and the fill side read correctly
any sewer main or easement under the run, a north point and a scale

Reading it for your own lot

RapidSiteplan reads the lot from its address in a minute: the boundaries, the contours, the house and the mapped services. Trace the wall where it goes and the sheet gives the height of each section, the distance to the boundary and the clearance to the sewer. The retaining walls page shows the sheet, and the council pages for every state show what each council maps. Start with the address.

Common questions

How high can a retaining wall be without approval? Only up to the height your state or council sets, and a wall that holds up a driveway, a building or a slope, sits near a boundary or carries a fence can need approval below it. Past that point the wall needs approval and usually an engineer’s design. The certifier reads the height of each section from the site plan.