Boundary retaining walls and neighbours

Retaining walls built on or near a boundary affect two properties at once, since they can hold up a neighbour's land, carry their water, and need access from their side to build. Sorting out these issues before work starts avoids most disputes. Treat this guide as general information rather than legal advice.

Start by confirming the boundary

Old fences are often not on the true boundary. Before designing a wall near the line, get a surveyor to mark the boundary on site. Many walls end up partly on a neighbour's land simply because the builder followed an old fence line.

Plan for everything below ground too. Footings, drainage pipes, gravel backfill and any ground anchors all take up space. A wall that sits on your side at the face can still have a footing that crosses the line. Keep all parts on your own land unless you have the neighbour's written agreement, and in some cases a registered easement.

A retaining wall is not a dividing fence

The Dividing Fences Act 1991 sets out how neighbours share the cost of fences. Its definition of a fence expressly excludes a retaining wall. The fence cost-sharing process doesn't apply to the wall itself, though a fence built on top of it may still be covered.

Responsibility for a boundary retaining wall usually turns on its location, who changed the ground levels, and any agreements already in place. If this is unclear, get legal advice before you start.

The duty to support neighbouring land

In NSW, the Conveyancing Act 1919 imposes a duty of care not to do anything on land that removes the support it gives to neighbouring land. Excavating near a boundary, for a pool, driveway or level yard, can remove that support. The duty covers the natural ground and the water beneath it.

In practice, if you cut down near the boundary, you need a design that keeps the neighbour's land stable throughout construction and afterwards. That often means an engineered retaining wall, staged excavation or temporary shoring. A dilapidation report on the neighbour's buildings before work starts is also good practice.

Water and drainage

Changing levels near a boundary changes where water flows. Exempt retaining walls must not redirect surface or ground water, or move sediment, onto a neighbouring property. Approved walls are expected to manage water through their design and conditions. The drainage behind the wall must discharge to a legal point on your property, not over the boundary. Our guide on Why retaining walls fail: drainage and backfill basics explains how this works.

Getting access to your neighbour's land

Building right on the boundary line often needs room to work from the other side. The simplest path is an agreement with your neighbour, in writing, covering timing, the area used, and restoration.

If agreement can't be reached, the Access to Neighbouring Land Act 2000 allows you to apply to the Local Court for an access order. Key points:

You must have made a reasonable effort to reach agreement first.
Affected people are entitled to 21 days or more notice of the application, unless the court directs otherwise.
The court considers whether the work could reasonably be done without access, and whether access would cause unreasonable hardship.
The person granted access must restore the land as far as practicable, and compensation for damage can be ordered.

Approvals for boundary walls

A boundary wall is more often caught by approval and engineering requirements than one in the middle of a yard. Height is the first test. See our guide on Retaining wall heights: when you need approval and an engineer. Where a wall is part of a CDC or construction certificate, the certifier will look at the engineer's design, footing location, drainage and how neighbouring structures are protected.

Talk to your neighbour early. Show them the plans, explain how long the work will take, and agree on access and restoration. It costs little and avoids most problems.

CertifiBuild certifies retaining walls as part of Class 1 and Class 10 projects across NSW. Request a quote, or see how our certification process works.

Local help across NSW

CertifiBuild certifies Class 1 and Class 10 work in 39 council areas. Local rules on these council pages are a good place to start: North Sydney Council, Campbelltown City Council, Lane Cove Council, Inner West Council, Northern Beaches Council, City of Canada Bay.

Suburb pages with local planning notes: Cremorne Point, Eagle Vale, Greenwich, Kirribilli, Lavender Bay, Marrickville, Newport, North Strathfield, Northbridge, Seaforth. You can also browse every service area.

Retaining walls on the boundary: neighbours, footings and access