Engineered & Certified Retaining Walls

Above a certain height, and in any situation where there is load behind it, a retaining wall stops being landscaping and becomes structural work with approval and certification requirements attached.

Which walls need approval, and which are exempt, is set by state legislation and the local planning scheme, and it turns on the height, on what sits behind the wall and on where the wall is. Both sets of rules get amended, so check the current position for your own wall rather than relying on this page.

When a wall crosses the line

Height is the obvious trigger. Beyond the threshold set in the regulations, a wall generally requires building approval and a structural design.

Surcharge is the trigger people miss. A surcharge is any additional load behind the wall beyond the soil itself: a driveway or parking area, a building or shed footing, a pool, a slope continuing upward above the wall, or another retaining wall above it. A wall well under the height threshold can still need engineering because of what sits behind it, and a low wall holding up a driveway is carrying vehicle loads that a garden wall never sees.

Proximity matters too. A wall close to a boundary, a structure or a services easement brings other considerations, and a wall that supports a neighbour’s land is a legal question as much as a structural one. That is covered in retaining walls on a boundary.

What the engineering actually produces

A structural design based on the site: the soil conditions, the retained height, the surcharge, and the drainage. From it come the specification of the wall itself, the footing sizes and depths, the reinforcement, and the drainage requirements.

That last point is worth drawing out. Engineered walls are designed on the assumption that the drainage is present and working, because designing for a permanently saturated backfill would make most walls uneconomic. The certification is not a guarantee that survives the drainage being left out or allowed to block, which is why the drainage detail is part of the design rather than a separate decision.

The paperwork, and why you want it

At completion there should be documentation: the engineering design and the certification that the wall was built to it, plus whatever the approval process required.

Keep it. It is what a purchaser’s building inspector asks for, what an insurer wants after a slip or a failure, and what a council asks about if a question is ever raised. An unapproved structural wall is a problem that stays with the property, and it surfaces at the moment you are least able to deal with it.

Where we sit

Engineering is arranged and priced into the quote rather than presented as an extra afterwards, and the approval process is handled rather than handed back to you as homework. If a wall does not need engineering, you will be told that too, rather than sold a certificate for a garden bed.

Ring 0468 066 055 with the height and what is behind the wall.