Plan Change 120 – What It Means for Ground Risk in Auckland Developments (PC120)
- Sam Gibb
- Nov 13
- 3 min read
Auckland Council’s Plan Change 120 (PC120) introduces major changes to how land development and housing intensification are managed across the region. While much of the discussion has centered on zoning and density, one of the biggest shifts for developers and designers is in the management of natural hazards and geotechnical risk.
At its core, PC120 aims to enable more housing – but only in places where it’s safe to do so. That means greater scrutiny of ground conditions, slope stability, and natural hazard exposure before development proceeds.
Key Geotechnical Issues Highlighted by PC120
PC120 strengthens the link between planning decisions and ground risk, with hazard overlays and mapping now having a more direct influence on what can be built and where. The main areas of concern include:
Landslide Susceptibility
Developments on or below steep ground are now more tightly controlled. The Council’s updated mapping highlights slopes susceptible to landsliding or long-term creep, and developers must show that proposed works won’t reduce stability or increase risk to neighbouring sites.
Coastal Erosion and Inundation
Coastal hazard overlays now reflect climate change projections and sea-level rise. This means more emphasis on long-term resilience – setbacks, elevated floor levels, and erosion protection works are increasingly required.
Flooding and Overland Flow
Urban and river flooding hazards have been reinforced in PC120. Civil and geotechnical design now need to work together to ensure new developments don’t exacerbate flooding and that structures remain resilient under flood conditions.
Liquefaction and Groundwater Hazards
Sites underlain by loose, saturated soils – especially in reclaimed or coastal areas – may trigger liquefaction assessments. Dewatering and excavation stability also remain key consenting issues for basements and service trenches.
Cumulative and Off-Site Effects
PC120 reinforces that developments must not worsen hazards for adjacent sites or public infrastructure. Retaining walls, earthworks and drainage design must be assessed for their wider impact.
What Developers and Designers Need to Do
If you’re planning a new development, subdivision, or intensification project, PC120 means geotechnical risk needs to be addressed earlier and in more detail.
Here’s a practical checklist:
Check the hazard overlays early.
Review the PC120 mapping for slope instability, flooding, coastal inundation, and liquefaction susceptibility.
Get a geotechnical desktop review.
Before design progresses, have a Geotechnical Engineer prepare a brief review confirming the site’s known hazards and the likely level of investigation required.
Undertake site-specific investigation.
Boreholes, test pits, groundwater monitoring, and analysis of slope stability or liquefaction potential are now routine expectations for consent-grade reports.
Design for resilience.
Incorporate foundation systems, drainage, and retaining solutions that directly address the site hazards – not just to meet Building Code, but to satisfy the Auckland Unitary Plan and PC120’s resilience objectives.
Engage early with Council.
Early technical discussions reduce rework and help align your geotechnical, civil, and planning documentation before lodgement.
How Gibb Ritchie Geotechnical Engineers Can Help
At GRGE, we help developers and design teams navigate the new PC120 requirements efficiently and confidently. Our team of Chartered Engineers and Geologists can provide:
Desktop screening reports identifying relevant PC120 overlays and hazard triggers
Site investigations and foundation assessments to support Building and Resource Consents
Slope stability and retaining wall design compliant with Auckland Council standards
Liquefaction, settlement and dewatering assessments for high-risk sites
Peer review and PS4 certification for consent and construction sign-off
Whether your project involves a single infill dwelling or a large-scale development, understanding the geotechnical implications of PC120 early will save time, reduce cost, and keep your project compliant.
Need Support?
Contact Gibb Ritchie Geotechnical Engineers to discuss your site. We can help you determine whether PC120 affects your property and provide the level of assessment required to move forward with confidence.
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