Background
MBIE amended Acceptable Solution (B1/AS1) in November 2019 to acknowledge liquefaction prone-ground is not exclusive to Canterbury region and the requirements should therefore be extended to all of New Zealand. The amendment facilitates the design of house foundations to
- Ensure new buildings (especially residential buildings) are designed and built with the right level of resilience to appropriately manage liquefaction related risk with cost effective solutions.
- Reduce the likelihood of extensive and catastrophic foundation failures where liquefaction risk is high across New Zealand
- Provides clarity to both Territorial Authorities (TA’s) and engineers ensuring new building foundations are being built safely and resilient enough to withstand risk on liquefaction-prone ground.
The change has a two year transition period starting from 29 November 2019 until 28 November 2021. The reason for this transition period is to allow TA’s time to complete liquefaction vulnerability mapping.
Due to COVID-19, TA’s around New Zealand may have experienced delays and disruption preparing to or in the process of completing mapping of liquefaction-prone ground, while this also delayed communications from MBIE.
Impact of good ground definition change
In essence, the change revokes the use of a ‘deemed to comply’ pathway for foundations unless the ground has been assessed and or categorised as not being liquefaction-prone – i.e. good ground. While there is an established framework for carrying out liquefaction mapping issued by MBIE, MfE (2017), there is no consistent approach (nationally) to demonstrate compliance with the Building Code.
In addition, BCA’s/TA’s have indicated the need for substantial technical and regulatory guidance supported by information and education to support them map their region.
Who is affected?
These changes will affect several different stakeholders such as TA’s, Building Consent Authorities (BCA’s), designers, engineers and other end users. Feedback from the public consultation period indicated the following:
- A small number of councils expressed concern in completing liquefaction mapping within the proposed transition time.
- Information (technical and regulatory) and further education was requested to target TA’s, BCA’s and other stakeholders to make the transition as smooth as possible.
Benefits from this change
The change promotes safer and more resilient foundations for all of New Zealand and mapping liquefaction-prone throughout New Zealand, will help the industry avoid disruption and building owners incurring extra costs.
The cascading effect of natural hazards is difficult to measure/ quantify. However, dependant on the level of detail the completed mapping to in a particular region, understanding the risk and severity associated with the ground condition alongside a good foundation design could help reduce/ mitigate the impact of cascading hazards.
What is MBIE doing?
MBIE understands that mapping for natural hazards (especially liquefaction) varies around the country with some TA’s or regions well ahead of the requirement while other TA’s require more support. So it is very important that MBIE takes a comprehensive approach to promoting compliance when the changes come live post 29 November 2021.
The framework for implementation of “Good Ground” definition change will involve a two phased approach:
Phase 1: Creating flowcharts and methodology statement for regional liquefaction assessments
Phase 2: National technical information that includes foundations and performance objectives
MBIE is currently finalising the publication of Phase 1 information. For the latest information, please visit building.govt.nz (https://www.building.govt.nz/building-code-compliance/geotechnical-education/ensuring-new-buildings-can-withstand-liquefaction-risks).
What to expect before the transition period finishes?
Other than the information expected later this year, It is expected the work associated with the transition would continue to ramp up from now until November 2021 with the intent to increase collaboration with the sector and relevant stakeholders. MBIE intends to carry out this in collaboration with other agencies (like EQC & MfE) and convey messages through Engineering
New Zealand digital channels.
