RETAINING WALLS

A retaining wall is not a fence (although it can serve as a footing for a fence). The law about retaining walls is principally found under the common law of nuisance and, where retaining walls were constructed after 15 January 1994, under the Development Act 1993 (SA).

Who is responsible for a retaining wall?

The most important factor in answering this question is determining the natural state of the land, as land in its natural state needs no support. It is only when the natural land is altered that support is required.

As a ‘rule of thumb’ each owner is responsible for retaining the portion of earth that they (or the previous land title holder) have altered from the natural ground level. This could be ‘fill’ placed on top of the natural ground level or excavation below the natural ground level.

Where both parties benefit from the existence of the retaining wall, then it is reasonable that both parties will contribute to the erection and/or maintenance of the retaining wall.

Where one party fills and the adjoining owner excavates, each party is liable to the proportion that the retaining wall supports the fill or excavation. For example, if one neighbour fills 300mm above the natural ground and the adjoining neighbour excavates 700 mm below the natural ground, then the neighbour excavating is liable for 70% of the cost and the neighbour that fills is responsible for 30% of the 1 metre retaining wall.

Any party can alter the natural state of their land (subject to development controls), but with this ability comes the obligation to support the adjoining natural land.

Classification of retaining walls under the Development Act 1993 (SA)

A ‘retaining wall’ falls within the definition of ‘structure’
A ‘structure’ falls within the definition of ‘building’
A ‘building’ (construction, demolition or removal, including incidental excavation or filling, unless excluded by Regulations [Development Regulations 2008 (SA) Schedule 3 section 4 (1) (i)] falls within the definition ‘building work’)
‘building work’ falls within the definition of ‘development’ ( Development Act 1993 (SA), s4)

Under s.32 of the Development Act 1993 no development may be undertaken unless it is approved.

When is development approval required?

Development approval is required under s.32 of the Development Act 1993 (SA) when:

fill of greater than 200mm high is to be retained and is within 600 mm of the boundary [Development Regulation 75 (2) (c)]; or
a retaining wall of greater than 1 metre is proposed (Development Regulations 2008 Schedule 3); or
the proposed excavation or fill [‘prescribed work’ - S60 (1) Development Act 1993 (SA)] may affect the stability of the land.

A retaining wall of less than 1 metre may affect the stability of the neighbours land dependent upon the distance the retaining wall is away from the boundary line [Development Regulations 2008 schedule 15]. For example, if the retaining wall is 200mm from the boundary a retaining wall over 700mm in height will fall within the definition of ‘prescribed work’ under s.60(1) and require approval.

Obligations for the building owner if retaining wall is a development

Once it is determined that the excavation or fill (‘prescribed work’) may affect the stability of the neighbours land the building owner must under s.60(1):

serve notice of intention to perform the building work and the nature of that work on the owner of the adjoining land; and
provide this notice at least 28 days prior to the commencement of building work; and
take precautions as prescribed to protect the adjoining land; and
at the request of the adjoining owner, carry out such other building work as is authorised by the regulations [Development Regulation 75(3)]; and
comply with any condition imposed by the approving authority.

A proposer who fails to serve a notice or who fails to carry out work specified after a notice faces a fine of up to $10 000 [s.60(2)].

Building work the adjoining owner can request [Development Regulation 75(3)] includes:

requiring the owner to shore up any excavation work; or
underpin, stabilise or otherwise strengthen the foundations of any building as specified by a professional engineer engage by the adjoining owner.
Payment of the reasonable costs of the professional engineer to provide a report and plans and specifications.

Determining who bears the cost

To determine who bears the cost, following will need to be considered:

what the natural level of the land was; and
if there has been any alteration to this level due to fill or excavation by any party; and
whether one or both parties has benefited from the retaining wall.

Erection of a retaining wall

Where only one party benefits

A building owner that excavates or fills their property for their sole benefit has the following obligations:

Under the Development Act 1993 (SA) - to obtain approval to perform ‘building work’ that affects the stability of adjoining land; and
Under common law - to support the natural state of land; and
To pay for all costs associated with the retaining wall.

Where both parties benefit

Where both parties benefit from the erection of a retaining wall, then it is reasonable that both parties will contribute to the erection or maintenance of the retaining wall. If the parties cannot agree on their contribution to costs then the following guide can be of assistance.

Where one party fills and the adjoining owner excavates, each party is liable to the proportion that the retaining wall supports the fill or excavation. E.g. if one neighbour fills 300mm above the natural ground and the adjoining neighbour excavates 700 mm below the natural ground, then the neighbour excavating is liable for 70% of the cost and the neighbour that fills is responsible for 30% of the 1 metre retaining wall.

If agreement can’t be reached between the neighbours, then, application can be made to the court for determination of each neighbours costs [s. 60(3) Development Act 1993 and Development Regulations 75(3)].