Does a Retaining Wall Need Approval in Queensland?

This comes up on almost every enquiry, usually as “I was told anything under a metre is fine”. That is roughly the shape of the rule and it leaves out the part that matters most.

Approval rules for this work sit in state legislation and in the local planning scheme, and both get amended. Nothing below is a ruling on your wall: check it against your own council or a building certifier before anyone starts digging.

Height is the first trigger

There is a height below which a straightforward retaining wall generally does not require building approval, and above which it does. That threshold is where the “under a metre” advice comes from.

Measured height is the retained height, from the bottom of the wall to the top of the retained material, not the exposed face. A wall whose base sits below finished ground level is taller than it looks.

Surcharge is the trigger people miss

A wall under the height threshold can still require approval and engineering if there is a surcharge behind it. Surcharge is any load on the ground behind the wall over and above the soil itself:

A driveway or any area vehicles use. A building, shed, tank or footing within the zone of influence behind the wall. A swimming pool. A slope that continues rising above the top of the wall rather than levelling off. Another retaining wall above it, which is the one that catches people terracing a steep block.

A low wall holding up a driveway is carrying loads a garden wall never sees, and treating it as exempt because of its height is the single most common mistake in this area.

Walls close together

Two walls stacked up a slope interact. The upper wall’s load transfers into the ground behind the lower one, and if they are close enough they have to be designed as a system rather than as two independent walls that happen to be near each other.

The spacing at which that stops mattering depends on the heights and the ground, which is exactly the kind of question engineering exists to answer.

Boundaries

A wall on or near a boundary, or one supporting a neighbour’s land, brings obligations that are separate from the building approval question. That is covered in retaining walls on a boundary.

What you should end up holding

Where approval was required: the approval documentation and the final certification. Where engineering was required: the design and certification that the wall was built to it. In all cases, a written scope stating what went behind the wall.

Keep it with the house papers. Unapproved structural work does not cause problems while you live there. It causes them when you sell, when you claim on insurance after a failure, or when a neighbour raises it.

If you are not sure which side of the line your wall sits on, ring 0468 066 055 and describe the height and what is behind it. If it does not need approval you will be told that.