Retaining Wall Information
In Queensland, retaining walls are classified as ‘buildings/structures’ and as such they should be contained within the land being retained, i.e. positioned inside or on the boundary of the retained land, otherwise the laws relating to encroachment and others could apply. It is also important to note that the Building Act 1975 requires any retaining wall over 1m in height to have local authority approval and this will involve design and certification from a structural engineer (RPEQ). The act does not differentiate between a retaining wall in a garden area and a retaining wall which is part of a structure.
Where there is a retaining wall on site constructed with materials known to deteriorate (for the most part this relates to treated timbers-particularly hardwood), which will require an obvious need replacement in the future, you should obtain advice from an appropriately licensed and suitably qualified QBCC licensed contractor, so that any replacement costs can be determined and advice can be obtained on future issues which may arise with the walls. Obviously where the wall is in excess of 1 metre in height, you will need to obtain additional advice from an RPEQ, to ensure compliance is maintained with the design and installation of the wall.
In relation to the use of timber for retaining walls, it is known that the longevity of hardwood walls are significantly less than that of pine, although the strength of hardwood retaining walls is far superior to that of pine. The predominant reason for this is that pine, being a softwood timber, is far better equipped absorb the CCA preservative treatment then the very durable hardwood species of timber.
Subject to obtaining appropriate legal advice, it is our understanding that in line with the above, the responsibility for retaining walls remains with the owner of the land being retained. If the retaining wall was created by an adjacent landowner following landscaping or site development works on their land, then the responsibility transfers to that land owner and successive owners as the need for a retaining wall only resulted following changes to the natural ground level created by the property owner who first initiated changes to the natural ground level. In summary, the property owner who created the need to retain the ground and successive owners have ongoing responsibility for the lands retention however where a dividing retaining wall is of benefit to both property owners, then the costs of maintenance/repairs/replacement should be jointly shared (subject to legal advice). Generally, the responsibility for the placement/replacement and repair of dividing fences which are often placed on top of such walls can be shared by adjoining owners (Dividing Fences Act 1953, as amended).
Quite frequently and in particular with older properties, the existence of a retaining wall and/or fence line may not truly represent the actual boundary line(s) and in all cases (assuming it has not been done already) it is strongly recommended that a determination on the actual boundary line be provided by way of a formal identification survey carried out by a QBCC licensed surveyor. This type of survey would identify the actual boundaries for the block and can avoid costly and unnecessary mistakes during development and also provide a formal piece of documentation to refer to in the event of a dispute between neighbours.