Retaining wall on the boundary with a neighbour dispute
A builder is constructing a new dwelling on a sloping site. The design includes a 1.8 m high retaining wall along the rear boundary to create a level courtyard. The neighbouring property sits lower. During excavation for the wall footings, the excavator operator reports that the neighbour's existing timber fence is leaning and that a crack has appeared in the neighbour's brick garage wall about 3 m from the boundary. The engineer's drawing specifies a cantilevered concrete sleeper wall with strip footings, but the geotechnical report (which the builder has now read) recommends a bored pier design where fill exceeds 1.5 m. The fill at the rear boundary is approximately 2.2 m. The neighbour has threatened to contact the council.
1. What immediate steps should the builder take, and what does the discrepancy between the drawings and the geotechnical report mean?
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The builder should stop excavation near the affected area immediately, secure the site, and arrange for the engineer to attend. The crack in the neighbour's garage and the leaning fence are indicators of ground movement that may be caused by the excavation, and continuing could worsen the damage and the builder's liability.
The discrepancy is significant. The engineer's drawing specifies a cantilevered sleeper wall on strip footings, but the geotechnical report recommends bored piers where fill exceeds 1.5 m, and the fill is 2.2 m. The builder should not resolve this by choosing one document; the engineer must reconcile the design with the geotechnical recommendations and issue a revised design. If the builder proceeds on the drawing without that reconciliation, the builder carries the risk of a design that is unsuitable for the actual ground conditions.
The builder should also document the neighbour's property condition now - dated photographs, a dilapidation report if possible - and notify the neighbour and the building surveyor in writing of the incident and the steps being taken. Early notification is far better than waiting for a council complaint.
2. What are the builder's obligations regarding the neighbour and the retaining wall approval?
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The builder should check whether the retaining wall is included in the building approval and whether it required development consent, particularly given its height and position on the boundary. A 1.8 m wall with 2.2 m of fill is a significant structure, and the approval documents should be checked for the wall's design, siting and any conditions about excavation near the boundary.
The builder should also consider the legal framework for excavation affecting adjoining land, which typically imposes a duty to support the neighbour's land and to notify before excavation. The builder should advise the owner to notify their insurer and, if the neighbour's damage is confirmed as caused by the works, arrange assessment and repair rather than disputing it.
Communication with the neighbour should be through the owner or the builder's representative in writing, factual and without admissions of liability beyond what is known. The builder should not promise to pay for repairs before causation is established, but should commit to investigating promptly. Council and the surveyor should be kept informed if the damage is structural.