Landslides, slumps and soil erosion can undermine a building structure.

The risk is likely to be high where the site:

• has been substantially altered through earthworks or removal of vegetation
• has a river or beach frontage
• is at the top of a cliff
• is on a faultline
• is sloping and a in high rainfall area where the soil readily becomes saturated
• has had mining activity in the past
• is in a geothermally active area.

Visual signs of slipping and slumping

Visual signs of potential slipping or slumping include:

• soil cracking parallel to the top of a bank
• a hump in the soil at the base of the bank
• where power poles, trees or fence posts are on a lean
• a hollow in the centre of a flat area of ground
• an undercut bank
• a bank cut steeper than the angle of repose for the soil type – see the table below.

Angle of repose	Soil type
30º	Soil
33º	Sand
25-40º	Dry sediment

In some parts of the country, expansive clays may also pose a risk to the stability of the building as the clays will shrink and swell between wet and dry parts of the year.

Gathering information

Observe the site for visual signs of past or potential landslides, slumps or erosion. Talk to neighbours who may be able to provide information about the history of the site regarding slips or soil erosion.

The local council should have information on past landslides, slumps and soil erosion within its boundaries. Many councils have online maps of natural hazards that sometimes include landslide hazards. Aerial photos can give an indication of areas that may be at risk from slipping or soil erosion.

A project information memorandum (PIM) or land information memorandum (LIM) for a property should contain information the council has about the risk of hazards such as slips and erosion.

Consider the potential impact of slips or slumps on stormwater and sewer systems. There is provision under section 71 of the Building Act 2004 for the council to refuse to grant a building consent if the land is at risk of a natural hazard, such as erosion, flooding, subsidence, or slippage, or if the building work itself is likely to accelerate the problem.

Natural Hazards Commission cover for landslides

New Zealand residential buildings that have a current house insurance policy that includes fire insurance are covered against natural disasters with NHCover provided by a government body, Natural Hazards Commission Toka Tū Ake (formerly EQC). Within certain limitations, it insures against physical loss or damage resulting from a natural disaster.

In addition to the cover for buildings, NHCover provides cover for:

• land under a home or outbuildings
• land within 8 metres of a home or outbuildings
• land that is part of (or supporting) the main access (the driveway) up to 60 metres from a home
• bridges and culverts within the above areas
• some retaining walls supports necessary to support or protect a home, outbuildings or insured land (including the main access way).

Cover does not include paving such as concrete or asphalt on the access way.

Private insurers do not normally offer any significant cover for land damage.

 

Updated: 26 July 2024