Building on land subject to natural hazards

You need to consider how natural hazards may affect your building and any implications it will have on your insurance. You should therefore identify known natural hazards on the site or location plan and seek advice about these from Environment Southland prior to applying for your building consent.

Where Council identifies that the land on which the work is proposed is subject to natural hazards, Council will consider if the work is major or minor and what affect the work will have on the hazard.

Depending on the circumstances, the consent could be refused or granted subject to building modification (e.g. floor height) and/or subject to a condition that a natural hazard notification is placed on the title (this will incur additional fees) or no additional action could be necessary. Natural hazard means any of the following:

• 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.

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.