Retaining wall certification

Other exempt rules for walls and earthworks

Exempt walls and earthworks need to keep 40 m or more away from any natural waterbody, such as a creek. The work must not redirect surface or ground water, or let sediment wash onto a neighbour's property.

Stepping walls down a slope? Keep each one 2 m or more, measured horizontally, from every other retaining wall you build. Exempt earthworks are not allowed on a heritage item, and in a heritage conservation area they must be in the back yard. Exempt walls still need to be structurally sound and comply with the building code. Exempt means no approval, not no design.

When do I need approval and an engineer?

Approval is needed once cut or fill goes past 600 mm, whether up or down from ground level. Where your site and design comply, it can go through fast-track complying development. If not, you lodge a development application with council. Either way, plan on an engineer's design. The certifier has to be satisfied the wall suits its height, the soil and whatever load sits on top.

Height alone does not trigger a balustrade on a retaining wall. Barrier rules only come in if the wall is part of a set path, for example the route between the street and your front door. Any deck, patio or path along the top is assessed separately.

Where does the water go?

Water collected behind a wall needs a lawful outlet into your own drainage system. Drains or weep holes that empty onto the neighbour's land, or channel water along the boundary, can cause damage and disputes. Show the outlet on the plans and build it as approved.

Protecting your neighbour's land

Digging near a boundary can undermine the ground or footings next door. If your approval allows digging below the base of footings on neighbouring land, a standard condition applies. This includes land in a road or rail corridor.

You must protect and support the neighbouring building or structure from damage, at your own cost, and underpin it if needed. This does not apply if you own the neighbouring land, or if the neighbour agrees in writing that it should not apply.

Before digging starts, record the neighbouring property's condition with photos (a dilapidation report). It gives both owners a clear reference if questions come up later.

Can a sloped batter replace a wall?

Sometimes the simplest wall is no wall at all. The ABCB Housing Provisions, which form part of the NCC (National Construction Code), set the steepest angle a cut or a fill can be left at without any support. How steep you can go comes down to the soil.

In sand, both a cut and compacted fill are limited to a slope of 1 unit up for every 2 units across. Firm clay can be cut at 1 in 1, but fill on it still needs the gentler 1 in 2. Soft clay is not suitable for unretained fill at all. The soil class comes from the site classification, so a geotechnical report is useful at this stage.

If the level change needs a steeper face than that, or the batter would spill onto the neighbour's land, a wall becomes the practical answer. Exempt earthworks carry their own limit too: fill deeper than 150 mm must not take up more than 25% of the lot.

Which inspections does an approved wall need?

Retaining walls sit in Class 10, which means the state's critical stage inspection rules apply to whichever stages actually happen on your job. For most walls that means one visit once the footing trench is dug and before any footing goes in, and another before reinforced concrete is poured in place.

Where the wall's drainage joins the site stormwater system, the certifier must see that joint before backfill hides it. A final inspection follows at completion. Each visit has to be requested by the builder, or the owner-builder, no less than 48 hours ahead.

Backfilling too early is the usual mistake. Once the drain and footings are buried, the evidence is gone. A missed inspection must be reported to the principal certifier within 2 days. It can only be excused where the miss could not have been avoided and the wall is proven to be sound.

Walls near sewer and water pipes

Pipes under the yard change what you can build. To stay exempt, a wall needs a clear 1 m gap from any registered easement and from sewer or water mains. Any closer and approval is required, and the water authority may also have to accept the design.

In Sydney Water's area, its technical guidelines allow retaining walls beside sewers of 300 mm diameter or less, but no wall, support or footing may sit over a property connection point. A building plan submission must be accepted first, and a specialist engineering assessment may be needed. Raising or lowering the ground over a pipe also needs Sydney Water's acceptance, so piling fill on top of a sewer is not a free choice.

Maintenance holes must never be built over or buried under garden beds. The guidelines call for 1 m of clear working space around a maintenance hole. A service location diagram, bought from Sydney Water's Tap in service, shows where the pipes run. Get one before the wall is designed.

Building in a mine subsidence district

Parts of NSW sit above old coal workings. Inside a Mine Subsidence District, the work can need a separate sign-off from Subsidence Advisory, alongside the planning approval from council or a certifier. A short list of minor works is exempt under section 22 of the Coal Mine Subsidence Compensation Act 2017.

What applies turns on the kind of risk under the lot. Where old shallow workings create a pothole risk, applications are assessed by Subsidence Advisory itself. Any retaining wall taller than 1 m needs certification from a structural engineer that it will stay serviceable if a pothole 5 m across opens beneath it.

Where the risk is trough subsidence, the guideline for compliant designs does not allow a retaining wall built into the house to hold it up. Free-standing walls that support no building are allowed if they are designed to the relevant Australian Standards. Check the lot's status early, because the subsidence rules can change the type of wall you build.