Dividing fences are the source of a great deal of angst between new (and not so new) neighbours.
Dividing fences are covered by the Dividing Fences Act. In relation to dividing fences, the Department of Housing and Works has produced an excellent booklet – “Dividing Fences”, which can be freely downloaded at www.dhw.wa.gov.au.
Retaining walls that form part of a dividing fence are not covered by the Dividing Fences Act, but are governed by the rules of the local authority. Generally speaking, the property owner who changes the level of land, either by excavation or filling to ensure that there is no earth movement, is responsible for the cost of construction of the retaining wall, as well as any ongoing maintenance bills. Retaining walls are usually the responsibility of the owner on whose property the wall is erected.
To check your legal obligations and responsibility regarding retaining walls, you should contact the Building Department at your local council office. Requirements can differ between local governments.