Who is responsible for a retaining wall between two properties?

This is where people are most often surprised. A dividing fence has a statutory cost-sharing regime. A retaining wall usually does not, even when it sits on the same boundary and even when a fence sits on top of it.

The principle that usually decides it

Land is entitled to the support it naturally had. If one owner excavates or fills so that the other's land now needs support, the person who created that condition is generally responsible for providing and maintaining the support. That means the history of the earthworks matters more than the current appearance of the wall.

What to establish

• Which side was cut or filled, and when, which old aerial photography and council records can often answer.
• Whether the wall was built as part of a development approval, which may have imposed conditions on who maintains it.
• Whether the wall is wholly on one property or straddles the boundary, which needs a survey.
• Whether anything on the title, such as an easement or a registered agreement, deals with it.

Where a fence sits on top of a retaining wall, the two are usually treated separately: the fence under the fencing Act, the wall under general law. That can produce the odd result of shared responsibility for the top metre and sole responsibility for the two metres below it.