Neighbouring Site Issues
Sloping sites can create challenges when undertaking building development works. Typically, earthworks are undertaken on sloping sites to create level building platforms and/or suitable accessways or carpark areas. These earthworks can result in permanent batter slopes, which need to be designed/constructed to a safe batter angle, so as to prevent erosion or instability of the batter slopes.
On smaller sites, which are physically constrained and where it is not possible to fit in safe batter slope profiles, the batter slopes are generally permanently retained by retaining walls. Typically retaining walls, particularly on or close to the boundaries of neighbouring sites, need to be carefully designed and constructed, so as to not cause damage to the neighbour’s land (or buildings on that land.
The critical stage of any retaining wall construction is the excavation works, particularly when the wall is to be close to neighbouring site boundaries. If appropriate design works are not undertaken, it is not uncommon for contractors to excavate very steep temporary slopes adjacent to boundaries, in order to construct the retaining wall. If these temporary excavation slopes are too steep and left for long periods of time, these temporary slopes can sometimes be subject to failure, which can result in the loss of ground support to the neighbouring site. If this occurs, and you are the owner/developer who is undertaking the works, you could be in for big costs to remediate the damage to your neighbour’s property. These costs are amplified if the loss of ground support affects foundations supporting neighbouring buildings.
If you are undertaking building works on your property, you are legally required to ensure that the works do not result in damage to land or buildings on neighbouring properties.
Building works, which includes the construction of retaining walls, are subject to the requirements of the Building Act 2004.
Section 71 of the Building Act states:
“(1) A building consent authority must refuse to grant a building consent for construction of a building, or major alterations to a building, if-
- (a) the land on which the building work is to be carried out is subject or is likely to be subject to 1 or more natural hazards; or
- (b) the building work is likely to accelerate, worsen, or result in a natural hazard on that land or any other property.
(2) Subsection (1) does not apply if the building consent authority is satisfied that adequate provision has been or will be made to-
- (a) protect the land, building work, or other property referred to in that subsection from the natural hazard or hazards; or
- (b) restore any damage to that land or other property as a result of the building work.
(3) In this section and sections 72 to 74, natural hazard means any of the following:
- (a) erosion (including coastal erosion, bank erosion, and sheet erosion):
- (b) falling debris (including soil, rock, snow, and ice):
- (c) subsidence:
- (d) inundation (including flooding, overland flow, storm surge, tidal effects, and ponding):
- (e) slippage.”
It should also be noted, if the permanent retaining walls are not appropriately designed and constructed, and if they are close to the site boundary, that the walls may themselves be subject to displacement, that could result in localised ground subsidence behind the wall, which could adversely affect the neighbour’s property (resulting in a possible damages claim).
It you are undertaking building development works which involves excavations close to boundaries, my advice to you is to engage appropriately qualified and experienced professional engineers to provide earthworks design recommendations and to design any proposed permanent retention structures. It is recommended that advice also be sought as to an appropriate construction methodology and the stability of temporary (during construction) excavation slopes.
We always advise our clients, for these types of works, to also undertake a condition survey of any neighbouring sites, prior to undertaking any excavation works, so as to provide proof as to the condition of neighbouring land and buildings (prior to you undertaking any works). This advice has saved many of my clients from protracted litigation with neighbours regarding alleged damage to their properties, as a result of the construction works. If you can produce before and after photographs, which clearly indicate that a cracked footpath (for example) existed prior to you undertaking the construction works, then you can quickly put to bed any potential damages claim from a disgruntled neighbour.