I am building a house in an estate in QLD. One of the neighbours has asked me to split the cost of the retaining wall between us ($3,425 / 2). When I was buying the land the developer's sales person told me that the cost of the retaining wall would be my neighbour's expense. The neighbour's seller (a construction company) told him that the retaining wall would be my responsibility. I can see the pattern there now... So, what's the common rule, e.g. 50:50 cost split for the retaining wall in addition to the fence later on? Thank you in advance.