Hi, I have a similar situation that started 4 years ago when the neighbour sued me , claiming the boundary retaining wall was defective and it was my responsibility to fix it.
I am not a lawyer, by the way.
I defended the claim and, after being self represented for 3 years , eventually engaged a lawyer as I was out of my depth with the legalities.
This type of dispute can easily escalate, incur significant costs and take years to resolve, if ever.
Presumably both parties - claimant and defendant, would prefer not to pay for the repairs and are not prepared to start cost share negotiations immediately , so evidence must then be obtained to clarify the cause of the wall rotation.
My case took 4 years , 4 conflicting engineering reports and 20 court appearances to reach an end point. My engineer found the wall had rotated due to the actions of the neighbours' builder , 10 years earlier, who undermined it during siteworks.
The case was eventually dismissed on a legal technicality . The initial claim was found to be invalid/unlawful.
So, for an all -parties & court costs of an estimated $ 150,000 nothing useful was achieved and the wall remains untouched in its initial condition . Fortunately it is still standing for the moment.
I was advised that the owner of the higher property ( that's me ) is not necessarily responsible for repairs. That is just the starting point. It depends on the circumstances. Specifically who/ which party caused the failure.
Who built the wall? How old is the wall?
Why has it failed?
Is it a design defect?
Is it a construction defect?
Is it due to deterioration over time?
Was it damaged/undermined during the construction of the flats?
How serious is the defect? Is there a high risk of abrupt collapse or is it more likely to remain serviceable for years?
Then there is the issue of what the options are for repairs. The lowest cost repair option may require encroachment into the land on the lower side.
These queries can only be answered by obtaining expert reports.
if the wall is quite old , determining blame for the failure could be of little value as the original parties responsible may be long gone.
If the failure presents a real risk of collapse I suggest you may have to enter negotiations with the neighbour over cost sharing of the agreed repair solution.
