New buildings and liquefaction effects

Buildings categorised Importance Level 1 (IL1 under AS/NZS1170:2002) are minor structures as failure is not likely to endanger human life such, structures are typically:

• Structures with a total floor area of < 30m2
• Not used for human habitation
• Farm buildings, isolated structures, towers in rural situations
• Fences, Masts walls, in-ground swimming pools

IL1 buildings have no performance requirements under SLS seismic load conditions, and therefore have no amenity requirements relating to liquefaction induced ground deformation in response to an SLS design earthquake event (level of shaking).

However, IL1 structures do have performance requirements under ULS seismic load conditions. It is likely that a ‘life safety’ design requirement at Ultimate Limit State (ULS) for a 1/100-year event, should be able to be provided, in most cases on a TC2 site, by a suitably detailed structure on a TC1 type foundation system.

Understanding Technical Categories (TC1, TC2, TC3) : Technical categories

Buildings categorised Importance Level 2(IL2) and above will require a higher level of assessment and are typically:

• Residential, including ‘sleepouts’ built under Schedule 1 of the Building Act 2004
• Commercial
• Industrial
• Education, health care facilities etc

Informative only, regarding Building Importance Levels and the associated structures can be found here: A3 Building importance levels

Each site will be considered on its own merits, the designer is responsible for ensuring the building consent application contains enough geotechnical information to allow the Building Consent Authority (BCA) to establish compliance with the NZBC.

• The designer or their representative should ensure the site is correctly located within the applicable liquefaction hazard zone identified on the mapping provided here 
• Geotechnical investigations and analysis should be used to inform design where required
• Designers should consider more robust foundation solutions where ground performance is uncertain
• Site investigation and geotechnical assessment should be tailored to the complexity and risk of the development proposal
• Deep geotechnical testing and liquefaction analysis is likely to be required for high-risk sites
• A shallow geotechnical investigation may be sufficient for simple building work on low-risk sites
• All geotechnical information supplied as part of either a resource consent or building consent application will be added to a Council database so enhanced mapping can be developed over time, reducing the need for future site investigation

Note: The use of NZS 3604 for the design of the superstructure (i.e. everything from the ground floor plate up) is acceptable for the construction of any house within the scope of NZS 3604 (i.e. the dimensional limitations are adhered to, and the use is limited to Importance Level 2 (AS/NZS 1170.0))

Find more information using these links:

Liquefaction

Regional Liquefaction map

Ensuring new buildings can withstand liquefaction effects

Building on ground with liquefaction potential

A3 Building importance levels