Retaining walls look simple, but they hold back enormous forces. Getting the design and approvals right protects your property, your neighbour's, and your wallet. Here's a plain-English guide to where retaining walls sit in the NSW approval system.
The 600 mm and 900 mm thresholds
As a general rule, NSW councils require engineering design for any retaining wall over 600 mm in height. Walls over 900 mm — or walls with a surcharge load such as a driveway, pool or structure above them — typically need development approval or a Complying Development Certificate (CDC).
Even short walls benefit from engineering when there is sloping ground above, poor soil, or an adjacent structure adding load.
Choosing the right wall type
- Cantilever walls — reinforced concrete or block, efficient for medium heights
- Gravity walls — mass concrete or segmental blocks that resist by weight
- Anchored walls — tied back with soil anchors where space is tight
- Crib and piled walls — for difficult ground or tall retained heights
Don't forget drainage
The most common cause of retaining wall failure is water. Hydrostatic pressure behind a wall can double the load it was designed for. A proper design always includes subsoil drainage, weep holes or an aggregate drainage zone.
Walls on a boundary
If your wall sits on or near a property boundary, there may be obligations under the Dividing Fences Act and a need to notify your neighbour. We can advise on these requirements as part of the design.
Need engineering advice?
Our Registered Professional Engineers are here to help with your project.
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