Boundary Retaining walls - Who's Responsible?

Why there's a problem - some history:

Over the last forty years many retaining walls have been built with timber or constructed without engineering design or with insufficient durability. Today we are experiencing lots of calls from owners with retaining wall repairs and replacement problems.

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Who should foot the bill?
Before we start on this question one needs to understand that it's not the Surveyor's role to determine the answer to this question. The Surveyor's role is to determine where the boundary is and thereby where the retaining wall sits. The Surveyor cannot determine who should foot the bill, nor indeed, who owns the wall.

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We understand that these projects can often be an expensive and complicated construction. Usually, the person who first recognises the problem is the lower neighbour – who looks on to the wall. The neighbour on the higher ground may be unaware of any problem unless notified by their neighbour or perhaps they see a fence start to lean over.

There may be some discussion between neighbours about the condition of the wall and the costs of repair.
At this time people start questioning ownership of the wall - and responsibility for repair and costs. One of the neighbours will call us (usually the lower property) and request a survey to find out where the boundary lies and ownership of the wall. 

Some important and realistic points to consider:

The wall should be built wholly on the land that receives the benefit. That is the land that is being retained.

A retaining wall is built for a purpose. Generally, it's the property owner who also gets the benefit from the wall’s existence who should be responsible for the wall.

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This is not always the case however and we often see instances of people who get the full benefit of a wall built on their neighbours’ property.

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Unfortunately it's not always that clear cut or simple. It's not the Surveyors job to determine responsibility.

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Quite often there is a benefit to both parties. If the land was originally sloping and both blocks now have flat land, we can assume that there has been both cut and fill.

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This is often the case in new developments where the original developer sought to offer flat building blocks. Developers and builders will often cut and bench the whole estate to provide flat building pads to facilitate slab on ground construction.

The best (and sometimes only) way to determine cut and fill is to dig or drill a hole in the top section to determine the depth of fill behind the wall. If its all fill to the base of the wall there is no benefit to the bottom neighbour. It becomes clearer who may be responsible. Again, it's not the Surveyor's job to determine responsibility - they merely produce a survey that shows physical facts.

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Do both neighbours get benefit and share costs?
The situation outlined in the top diagram shown here on the right could be such a situation.

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The way forward:

There is an information gathering stage for any building project. Assess the issues and repairs, determine who gets benefit and if necessary, determine the boundary location. Discuss the result and try to come to a reasonable plan of action. This will usually involve a Survey. The best solution is served by goodwill between neighbours.

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Types of Surveys:

Partial Site Plan - useful for access, quoting and design of a new wall 
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Identification Survey - marks the boundary clearly for both parties and shows the position of structures