We own a property (built in the 70's) that is on a bit of a slope. Our neighbours behind have a nice flat backyard thanks to a retaining wall that sits on the boundary between us (they are uphill from us). I believe that our property is the original slope of the land and the adjoining properties suggest that I am correct. The retaining wall is very old and was built prior to either us or our neighbours buying our properties. The wall is not constructed properly (I am not a licensed builder but you decide - hollow cement blocks with no re-enforcing, concrete fill or concrete footings) and approximately 1.5m high at its highest point. The neighbours have a large tree on their boundary and the wall has now started to lean out towards us adjacent to the tree. A recent survey has the wall footings crossing the boundary from entirely on our side at one end to entirely on their side at the other end. I am concerned that if it collapses, we will have a very large tree through our roof and we could end up with their backyard in ours. We would be prepared to cover up to 50% of the costs but they are claiming it is our responsibility entirely. I have done a little research and have found that; "Since 2008, under amendments to the Dividing Fences Act 1991, section 3, an adjoining owner can seek a contribution for the carrying out of work to a retaining wall where the wall is necessary for the support and maintenance of a dividing fence." Retaining walls | Neighbours and the law Can anyone shed any more light on our situation?