Building on land subject to natural hazards

When you apply for consent for a new building, or a major alteration to an existing building, consider how the building could be affected by natural hazards, or how the work could accelerate or worsen a natural hazard.

Natural hazard dangers

The Building Act requires us to decline a building consent for work or major alterations to a building if:

• the land is subject to one or more natural hazards
• the work will accelerate or worsen the adverse effects of the natural hazard on that land or other property.
• This would not apply if we are satisfied that adequate provisions have been made to protect land, building and
  other property or restore any damage to that land or other property.

If Council is satisfied that provisions have been made to protect the building and not the land and the building consent is approved, a condition would be added to the building consent which requires a notice to be registered on the property title to ensure future owners of the land know about the potential hazard. For this reason, property owners are keen to ensure that their developers and designers demonstrate how protection of the land as well as the building has been achieved.

What is a natural hazard - according to the Building Act

The Building Act defines a natural hazard as land subjected to:

• erosion (including coastal erosion, bank erosion, and sheet erosion)
• falling debris (including soil, rock, snow, and ice)
• subsidence
• inundation (including flooding, overland flow, storm surge, tidal effects and ponding)
• slippage.

Hazards such as tsunamis or earthquakes are not regarded as natural hazards under the Building Act. Occasionally natural hazards may not be identified in Project Information Memorandums (PIMs) associated with your building consents, and there may be a need for the BCA to determine whether or not natural hazard provisions apply.

MBIE have recently put out some guidelines on Natural Hazards and the application of the legislation in regards to these. The following link is their guidance: Natural hazard guidance 

Changes to the New Zealand Building Code (NZBC) for dealing with liquefaction-prone land come into effect 29 November 2021.

The following information details the requirements to have specifically designed foundations for buildings on ground identified as liquefaction-prone ground after this date.

If you have any questions about the information on this page please talk to a building professional (e.g. architect or structural engineer) or contact Building Services on 0800 732 732 or email building-cs@southlanddc.govt.nz.

Background

Liquefaction is a natural process where earthquake shaking increases the water pressure in the ground in some types of soil, leading to temporary loss of soil strength. It can cause significant damage to land, buildings, infrastructure and the environment, as well as economic and social disruption.

The NZBC definition of ‘good ground’ as defined by New Zealand Standard NZS3604:2011 has now been amended to exclude ‘liquefaction’. The rationale for the change is to support safer and more resilient housing foundations for buildings on liquefaction-prone land.

This change has been made as a result of the experience of the Canterbury earthquakes, which generated widespread liquefaction, and subsequent recommendations made by the Royal Commission of Inquiry.

These regulations are already in place in the Canterbury region, and will now be extended to all New Zealand.

Liquefaction risk factors

The three key factors which influence whether liquefaction occurs and how severe the ground damage will be are:

• soil condition (material type and density)
• groundwater depth
• earthquake shaking (duration and intensity).

MBIE guidance on liquefaction can be found on the following links:

Building on ground with liquefaction potential

Identification, assessment and mitigation of liquefaction hazards

An application for a LIM would be advantageous to ascertain what information Council hold regarding liquefaction on your property.

Council will discuss with you any refusal or notification process relating to your consent.