Land Instability
The risk of ground movement including landslides, slope failure, subsidence, and land slippage that can damage buildings and infrastructure.
What is a Land Instability?
Land instability encompasses a range of ground movement hazards โ landslides, slips, rockfalls, subsidence (ground sinking), and creep (slow downslope movement). New Zealand's steep terrain, seismic activity, volcanic soils, and high rainfall make land instability one of the most widespread natural hazards affecting property.
Many desirable properties in New Zealand are built on hillsides with views, but slopes bring inherent stability risks. Heavy rain events regularly cause slips across the country, damaging homes, roads, and infrastructure. The risk is heightened during earthquakes and after vegetation removal.
Councils map areas of known or suspected land instability in their district plans and LIM reports. Properties in these zones may face building restrictions, requirements for geotechnical assessments, and engineered foundation solutions. Even properties outside mapped zones can be at risk if they're on slopes, near watercourses, or on fill (imported soil used to level a site).
Why It Matters for Due Diligence
Land instability can cause catastrophic damage to buildings โ from cracked foundations and tilting floors to complete destruction if a major slip occurs. Remediation of slip damage is extremely expensive and sometimes impossible. Properties on unstable land may be difficult to insure and hard to sell.
For any property on a slope, near a cliff face, or on filled ground, check the LIM report for land instability hazard overlays. Consider getting a geotechnical assessment, especially if you plan to build or modify the property. Look for visible signs of movement: cracked retaining walls, tilting fences, doors that don't close properly, or uneven floors.
How to Check
The LIM report will flag known land instability hazards. Council GIS hazard maps show areas of identified slope instability. A geotechnical engineer can assess the specific risk for a property by examining the soil, slope angle, drainage, and geological conditions. During physical inspections, look for signs of past movement: stepped cracks in walls, misaligned door frames, retaining wall failures, and ground surface irregularities.
Frequently Asked Questions
Is land instability covered by insurance?
Land damage from natural disasters (including earthquakes and storms) is partially covered by the Natural Hazards Commission (EQC) โ up to $300,000 for residential land. Private insurance covers building damage. However, gradual land movement (subsidence, creep) is typically excluded from both EQC and private insurance. Pre-existing instability is also generally excluded.
How do I know if a hillside property is safe?
No hillside property has zero risk, but a geotechnical assessment can evaluate the level of risk. The engineer will examine soil types, slope angle, drainage, vegetation, and geological conditions. They can recommend measures to reduce risk, such as retaining walls, drainage improvements, or specific foundation designs. Budget $2,000-$5,000 for a basic geotechnical assessment.
Related Terms
LIM Report
GlossaryA Land Information Memorandum โ an official council report summarising everything the council knows about a property.
Liquefaction
GlossaryA phenomenon where saturated, loose soil loses its strength during an earthquake and behaves like a liquid, causing the ground to shift, sink, or eject sand and water.
Flood Zone
GlossaryAn area identified by the local council or regional authority as being at risk of flooding, based on historical data and modelling.
Erosion-Prone Land
GlossaryLand identified as susceptible to erosion from wind, water, or other natural processes, potentially affecting the stability and usability of a property.
Resource Consent
GlossaryPermission from the local council to carry out an activity that affects the environment, required under the Resource Management Act 1991.
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