We live in Perth and we have a retaining wall issue with our neighbour. The Western Australian law from a previous...

We live in Perth and we have a retaining wall issue with our neighbour. The Western Australian law from a previous post on this site states

"The person who changes the land level by digging or building up is responsible for building a retaining wall to make sure that there is no risk of earth movement.

Any person buying a property with a retaining wall is responsible for maintaining it.
If both neighbours change the land level, then each neighbour will be responsible for building the retaining wall and maintaining it. The amount that you pay will depend on how much you have each changed the land level."

Now the situation is as follows:-

Our land level was raised about 200-300 mm about 15 years ago and a prefabricated concrete retaining wall was built to retain this difference in levels over a distance of about 3 metres along our neighboring boundary. Recently our neighbor has carried out extensive building additions to his house and he has excavated his land down by about 400 mm. He has also removed part of the prefab concrete retaining wall that was existing and has not replaced it with anything. Consequently we have soil slippage where there is now no retaining wall. We complained to the Council and they have inspected. They have stated that due the land levels difference being greater than 500 mm an engineered retaining is to be built with council approval required. They have also stated that since both properties' land levels have been altered that both owners should share the costs of erecting the new retaining wall.

We do not believe this is the correct advice in this case since we have already erected a sufficient retaining wall which was removed by our neighbor. In addition he is the one gaining the benefit of his excavation. Appreciate your advice.