Boundary retaining walls are among the most common sources of neighbour disputes in the Blue Mountains. On a hilly property where one lot sits higher than the adjacent lot, the question of who owns the retaining wall, who must maintain it, and who pays when it fails is genuinely complex, and often misunderstood.
The short answer under NSW law: the owner of the land that benefits from the retention (generally, the higher-side owner) bears the primary responsibility for maintaining the structure that retains their land. But the details matter considerably.
The Basic Legal Principle
NSW does not have a single specific “retaining wall” law. The relevant principles come from a combination of:
- Common law (tort): The duty of care owed by landowners to prevent foreseeable harm to others
- Conveyancing Act 1919 (NSW): Property and boundary provisions
- Local Government Act 1993: Council enforcement powers
- The specific property title documents: Easements, covenants, or encumbrances recorded on the title
The generally accepted principle in NSW courts and disputes:
The owner whose land would slide without the retaining wall is responsible for it.
In practical terms: if Property A sits higher than Property B and a retaining wall on or near the boundary holds back Property A’s soil from flowing onto Property B, then Property A’s owner is responsible for maintaining that wall.
Where the Wall Is Located Matters
Wall Entirely on Your Property
If the retaining wall is entirely within your property boundary (even if it’s right at the boundary), you own it and are responsible for it. The fact that it’s close to a neighbour’s land doesn’t change ownership.
Wall on the Boundary Line
Before assuming which side of the boundary a wall actually sits on, it’s worth checking rather than guessing, old survey pegs on sloped Blue Mountains blocks are often missing or disturbed. See our guide on surveyors and retaining wall boundary disputes for when it’s worth commissioning a registered surveyor to confirm the wall’s position before a liability conversation goes any further.
A wall built on the exact boundary line is more complex. In most cases:
- The wall belongs to both property owners (a shared structure)
- Both owners may have maintenance obligations
- Disputes about shared boundary walls are governed by the Dividing Fences Act 1991 (NSW), which covers dividing structures (though retaining walls are a separate issue from dividing fences)
- If a shared retaining wall fails, both owners may have contributed to the failure through their respective maintenance obligations
For a broader, plain-language look at how ownership is generally worked out for boundary retaining walls in NSW, see our Who Owns the Boundary Wall? guide.
A common point of confusion here is whether the Dividing Fences Act 1991 (NSW) covers a shared boundary retaining wall the way it covers a standard fence, it generally doesn’t. See our guide on the Dividing Fences Act versus retaining wall liability for where that legal line actually sits and why NCAT’s fencing cost-sharing process doesn’t automatically extend to the wall.
Where a fence sits on top of the retaining wall itself, the liability position gets more complicated again, the fence adds a structural load the wall may not have been designed for, and the two structures can have different owners and different legal frameworks governing them. See our Fencing on Retaining Walls guide for the height, structural, and liability considerations specific to that situation.
Wall Entirely on Neighbour’s Property
If a retaining wall is entirely on your neighbour’s land (even if it is clearly retaining your soil), the neighbour owns the wall, but this doesn’t remove your duty of care for the stability of your own land.
You cannot demand that a neighbour maintain their retaining wall in the absence of an easement or other legal obligation. However, if your land is imposing extra load on a neighbour’s wall (for example, you’ve added fill to your property that loads the wall beyond its capacity), you may be liable for damage to that wall.
Scenarios and Who Is Responsible
| Scenario | Likely Responsible Party |
|---|---|
| Wall on higher property’s land, retaining higher property’s soil | Higher property owner |
| Wall on boundary, retaining higher soil | Shared obligation (both owners) |
| Wall on lower property’s land, but higher property would slide without it | Higher property owner typically bears the duty |
| Higher owner adds fill, overloads existing wall | Higher owner |
| Lower owner removes support from wall’s foundation by excavation | Lower owner |
| Neither party has maintained a shared wall, and it fails | Both parties may bear some liability |
| Council enforcement order exists requiring repair | Order recipient bears the immediate responsibility |
These are general principles. Individual cases depend on the specific facts, the position of the wall relative to the boundary, any easements or covenants on the title, and what the respective owners have done to the wall over time.
When a Failing Wall Causes Damage
When a retaining wall fails and causes damage to a neighbour’s property, their garden, fencing, vehicles, or structures, the question of liability becomes urgent.
Liability for damage: The owner responsible for maintaining the wall may be liable in negligence for damage caused by its failure, if:
- The failure was foreseeable (warning signs existed and were ignored)
- The owner failed to take reasonable steps to maintain or repair the wall
- The failure caused the neighbour’s loss
Key issue: foreseeability. If a wall shows visible signs of failure (leaning, cracking, missing drainage) and the responsible owner ignores it, a court may find that the failure was foreseeable and the owner was negligent. If the wall failed suddenly and without warning, the liability position is more nuanced.
Insurance: Check your home and contents insurance policy. Some policies cover damage caused by structural failure of retaining walls, including damage to a neighbour’s property. Others exclude it. Know your policy before a problem arises.
What To Do If Your Neighbour’s Wall Is Threatening Your Property
If a retaining wall owned by your neighbour is failing and poses a risk to your property, see our step-by-step guide on what to do when the neighbour’s wall is failing onto your land for the full documentation and escalation process. In summary:
- Document the condition: Take dated photographs of the wall, particularly any visible lean, cracking, or soil spill.
- Notify your neighbour in writing: A letter or email noting your observations and requesting they have the wall assessed. Keep a copy.
- Check with BMCC: If the wall poses an imminent safety risk, BMCC can be notified. Council has powers to issue repair and maintenance orders to the responsible owner under the Local Government Act.
- Legal advice: If your neighbour refuses to act and damage occurs (or is imminent), legal advice on your options is appropriate. NCAT (NSW Civil and Administrative Tribunal) handles neighbourhood disputes that can’t be resolved directly.
- Urgent action: If the wall is imminently at risk of collapse and threatens immediate injury or property damage, this may be a matter for the police, council, or fire service, depending on the severity.
See [/guides/retaining-wall-failure-warning-signs/] for the warning signs to document.
What To Do If You Are the Owner of a Failing Wall
If your retaining wall is failing and could affect a neighbour:
- Act promptly: Get a professional assessment. A leaning wall that damages a neighbour’s property after you’ve been warned is a significantly worse legal position than one that fails without warning.
- Notify your neighbour: Inform them that you’re aware of the issue and taking steps to address it. This demonstrates good faith and may reduce the severity of any future dispute.
- Notify your insurer: Major repair works should be disclosed to your insurer, particularly if there’s a risk of damage to adjacent property.
- Get the repair done: See [/guides/retaining-wall-repair-vs-replace/] for repair options, and [/services/concrete-sleeper-walls/] or [/services/timber-sleeper-wall-replacement/] for the relevant service.
Blue Mountains Specific Considerations
In the Blue Mountains, boundary retaining wall disputes are particularly common because:
- Most lots have significant slope, meaning one property typically sits higher than the next
- Many of the retaining walls are aging timber sleeper walls from the 1970s, 1990s that are now failing
- The high-rainfall environment means failures happen quickly once drainage fails
- Heritage conservation area regulations can complicate the repair process (material constraints, DA requirements)
BMCC is active in responding to reported failing retaining walls that pose safety risks. If a wall failure has resulted in damage or an enforcement notice, contact BMCC and get legal advice promptly.
FAQ
My neighbour’s retaining wall is on our boundary and leaning toward my property, can I make them fix it? You can request they fix it in writing. If they refuse and the wall deteriorates further or fails, you may have legal recourse, particularly if damage results. Document the condition now and consider legal advice if the neighbour is unresponsive.
Who pays for a shared boundary retaining wall repair? If the wall is on the boundary and both properties benefit from it, cost-sharing is typical. The exact split depends on whose land would slide without the wall. A practical approach is for both neighbours to jointly engage a contractor and share the cost proportionally. See our guide on splitting replacement costs with a neighbour for practical cost-split templates and how to document the agreement.
Can BMCC force my neighbour to repair a failing wall? Yes, BMCC can issue a repair and maintenance order under the Local Government Act if a retaining wall is assessed as posing a safety risk. This is typically triggered by a complaint from the affected neighbour. Council will inspect and if the wall is deemed unsafe, the responsible owner receives a formal order to repair.
What if neither party wants to pay for a shared boundary wall repair? NCAT (NSW Civil and Administrative Tribunal) handles neighbour disputes including retaining wall liability. A mediator can sometimes achieve a cost-sharing agreement without litigation. Legal advice is recommended if negotiation breaks down.
If I repair my retaining wall, do I need to notify my neighbour? Yes, any retaining wall work on or near the boundary that may affect neighbouring land should be communicated to your neighbour. If a DA is required (wall over 1.0m), BMCC will notify adjacent landowners as part of the notification process anyway.
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