Site Analysis

Understanding all the features of a site, using and protecting the best, and minimising the impact of the worst.

Landslides, slumps and erosion

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
30 Soil
33 Sand
25-40 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. Aerial photos can give an indication of areas that may be at risk from slipping or soil erosion.

A land information memorandum (LIM) may contain information about slips and soil erosion.

Consider the potential impact of slips or slumps on stormwater and sewer systems. There is provision under section 72 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.

EQC cover for landslides

New Zealand residential buildings that have a current house insurance policy that includes fire insurance are covered against natural disasters (including natural landslips) with EQ Cover. EQ Cover is provided by a government body, the Earthquake Commission, and is government guaranteed. Within certain limitations, it insures against physical loss or damage resulting from a natural disaster.

In addition to the cover for buildings, EQ Cover 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.

In 2019, some of the details around EQ cover changed. Changes include:

  • The time limit on lodging a claim has been extended from 3 months to 2 years.
  • The cap on EQC residential building cover is increasing from $100,000 (+GST) to $150,000(+GST) from 1 July 2019. (Homeowners can get top-up insurance from private insurers to cover loss above this limit.)
  • The EQC has more flexibility around sharing property-related information necessary to settle insurance claims.

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

 

Updated: 17 June 2019