If you're thinking about carrying out building works, you'll need to consider whether there may be any natural hazards present, and how they could affect compliance with the Building Act 2004 and the New Zealand Building Code.
Sections 71-74 of the Building Act 2004 are concerned with building on land which is subject to a range of natural hazards, such as:
- falling debris (including soil, rock, snow and ice);
- subsidence;
- inundation (including flooding, overland flow, storm surge, tidal effects and ponding); and
- slippage.
Obtaining a building consent
New building work or major alterations should be designed with any natural hazard in mind. You can apply for a building consent to carry out work on land with hazards; however, you’ll need to demonstrate how you will protect the building, the land, and any other properties potentially affected by the work.
Section 72 of the Building Act 2004 requires Horowhenua District Council to consider building consents for new buildings or major alterations on land that is subject to a natural hazard and refuse to grant the building consent if the situation is made worse, or grant the building consent subject to Section 72 if the building work is subject to a natural hazard.
Title endorsements
When a building consent is issued subject to section 72, the Council must notify the Registrar-General of Land to arrange an endorsement on the Certificate of Title advising that the consent has been issued pursuant to section 72 of the Building Act 2004.
Identifying any hazards
A Property Information Memorandum (PIM) or Land Information Memorandum (LIM) will identify any hazards on file with Horowhenua District Council.
A PIM is a memorandum issued by Council and is a voluntary part of the building consent process. A PIM provides all information Council knows about your property and is specific to the building project. A PIM does not give any form of approval under the District Plan or Building Act. Contact Council’s Consents Team or your own planning adviser to determine whether your proposal complies with the District Plan. If Resource Consent is required it must be obtained before the building work can be started.
If you think natural hazards may apply to your project, Council recommends you seek professional or legal advice so you can make fully informed decisions. We recommend that if you are in one of these areas that you book a pre-application meeting to help you understand the possible hazards on your site.
More information about PIMs can be found on the Ministry of Business, Innovation and Employment (MBIE) website.
A New Zealand Building Code update, effective from 29 November 2021, prevents B1/AS1 from being used on liquefaction-prone ground. As part of these changes, liquefaction assessments need to be undertaken where the liquefaction vulnerability hasn’t been fully characterised and foundation design needs to be appropriate for the liquefaction category.
The change brought the rules that were in place in Canterbury to the rest of New Zealand, meaning robust foundations are required for liquefaction-prone ground.
MBIE has developed resources to help with the implementation of these changes, which are available on the Ensuring new buildings can withstand liquefaction effects page.
Liquefaction maps for the Horowhenua District
Tonkin & Taylor Ltd was engaged by Horowhenua District Council to undertake a high level liquefaction vulnerability assessment of our main urban areas and associated future growth areas identified the Horowhenua Growth Strategy 2040 and a more recent assessment was undertaken in June 2023. This assessment has been used to inform plan changes to progressively rezone growth areas within the Horowhenua District.
We've updated our online maps to include this information.
How to view the Liquefaction Risk maps online
To view this information on our Online Maps, please follow the steps outlined below:
- visit our Online Maps page and launch the Desktop version;
- on the top, right-hand side of the screen, select the 'Land' tab;
- under 'Layers' on the left-hand menu, select the '+' sign next to 'Hazard';
- select the 'Liquefaction Risk' layer.
If you need information about a specific property where the detail isn’t clear on the maps, please lodge an enquiry with our Customer Experience team.
A revised policy approach to liquefaction assessments for the Horowhenua District was adopted at a meeting of Council on 20 March 2024, following updates to liquefaction maps for the Horowhenua District.
The policy approach and associated decisions were based on a report and recommendations from geotechnical engineers from Tonkin & Taylor. A copy of the report is available below.
Appendix B - Options for Liquefaction Assessment in the Horowhenua District(PDF, 1MB)
Summary of Council decisions
Below is a summary of the Council decisions.
Adoption of 'Policy D' for Building Consents and 'Policy C' for Resource Consents
Council adopted Policy D for building consents and Policy C for resource consents. Table 1 below outlines the policy approach for different development scenarios.
Table 1: Horowhenua District Council policy approach for liquefaction assessment / mitigation options adopted in different development scenarios
| Table 1: Horowhenua District Council policy approach for liquefaction assessment / mitigation options adopted in different development scenarios |
| Development scenario |
Policy D - Building Consents |
Policy C - Resource Consents |
Sparsely populated rural area
(lot size >4 ha)
eg a new farm building |
Option 3 |
Option 3 |
Rural-residential setting
(lot size of 1 to 4 ha)
eg a “lifestyle” property |
Option 3 |
Option 3 |
Small-scale urban infill
(original lot size <2,500 m2)
eg demolish old house and replace with four townhouses |
Option 3 |
Option 3 |
Commercial or industrial development
eg a warehouse building in an industrial park |
Option 1 |
Option 1 |
Urban residential development
(typically 15-60 households per ha)
eg home in a new subdivision |
Option 3 |
Option 2 |
Notes:
- Option 1: No liquefaction assessment / mitigation provided to practitioners.
- Option 2: HDC endorse adoption of Canterbury guidance.
- Option 3: HDC provide Horowhenua-specific guidance.
Liquefaction Vulnerability Guidance
The liquefaction vulnerability guidance and associated screening tool were adopted and will be effective from 21 March 2024. This guidance can be viewed below.
Appendix B - Options for Liquefaction Assessment in the Horowhenua District(PDF, 1MB)
A modified version of the screening tool was adopted.
Appendix C - Revised Screening Tool(PDF, 717KB)
The minimum geotechnical investigations and reporting requirements for resource consents and building Consents using the screening tool is outlined in Table 2 below. The Minimum Geotechnical Investigations and Reporting Requirements for Resource Consents for Urban Residential Scale Development is outlined in Table 3 below.
Table 2: Minimum Geotechnical Investigations and Reporting Requirements for Resource Consents & Building Consents Using Screening Tool (Option 3)
| Table 2: Minimum Geotechnical Investigations and Reporting Requirements for Resource Consents and Building Consents Using Screening Tool*** (Option 3) |
| Liquefaction |
Geomorphic Terrain |
Minimum Geotechnical Testing Required |
Minimum Reporting Requirements |
| Unlikely |
Hills and ranges - where bedrock is likely to be present within 4m |
Ground bearing completed in accordance with NZS 3604 including bore holes / test pits by a CPEng structural engineer or geotechnical engineer*
|
- A description of the landscape and geomorphic terrain, confirmation that the site is within the "hills and ranges" terrain
- A site plan (to scale) showing the position of the proposed building and accurate location of the investigation sites
- Dynamic cone (Scala) penetration logs in accordance with soil logs at the site of each penetrometer test in accordance with NZS 3604 part 3.3
- Bore hole logs with soil logs** at the site of each penetrometer test
- Confirmation that site specific observations regarding soil types are consistent with the "hills and ranges" terrain
- Confirmation that there is hard rock or dense sediments within the upper 4m of the subsoil profile AND the material is likely to be bedrock – OR – state refusal and outline likely reasons for refusal (with reasons linking back to subsoil profile)
|
|
Unlikely
|
Hills and ranges - where bedrock is not likely to be present within 4m
Alluvial & marine terrace
Alluvial plains & river flats
Swamps & wetlands
Active coastline & dunes
Relic dunes
|
Shallow ground investigations in accordance with NZS 3604 with a bore hole / test pit to 3-4 metres. Investigations to be carried out by a CPEng structural engineer or a geotechnical engineer*
|
- Desktop review including references to HDC liquefaction maps adopted in 2024 and local geotechnical data
- A description of the landscape & geomorphic terrain
- A description of the proposed development
- A site plan (to scale) showing the position of the proposed building and accurate location of the investigation sites
- Dynamic cone (Scala) penetration logs in accordance with soil logs at the site of each penetrometer test in accordance with NZS 3604 part 3.3
- Bore hole / test pit to 3-4 metres with soil logs** at the site of each penetrometer test
- Provide an assessment of liquefaction risk, based on on-site observations and referencing the screening tool***
- On-site assessment of groundwater levels or groundwater data from nearby resources where it is not possible to assess groundwater depth, including seasonal fluctuations in groundwater.
- The qualifications and practice area of the engineers involved in the investigations, reporting and peer review (where applicable).
- Recommendations for locations of future buildings and infrastructure (resource consents only)
- Recommendations for future building foundation design
- Where liquefaction category is assumed or confirmed to be high, input from a geotechnical engineer* is required with recommendations for mitigation and / or foundation design for future buildings.
The following may also be required in accordance with the screening tool***:
- On-site assessment of groundwater levels. Groundwater data from nearby resources may be accepted where it is not possible to assess groundwater depth. This should include any seasonal fluctuations in groundwater.
- An assessment of crust thickness (as the depth to the first liquefaction-susceptible soil layer (eg non-plastic silt, sand or loose gravel) which is below the expected long-term average groundwater level)
- Where crust thickness is less than 3 metres, provide an assessment of lateral spread – this can be based on the distance to and height of any free faces in accordance with the screening tool***
|
| Undetermined |
| Possible |
|
|
Notes:
* Geotechnical engineer means Chartered Professional Geotechnical Engineer or Professional Engineering Geologists (PEngGeol) in the practice field of geotechnical. Where the testing and reporting is carried out by a structural engineer, the guidance of a geotechnical engineer should be sought in accordance with “Geotechnical Input Decision Chart for Structural Engineers” from Engineering New Zealand.
** Soil logs are to be in accordance with “Field Description of Soil and Rock – Field Sheet – New Zealand Geotechnical Society”
*** Appendix C - Revised Screening Tool(PDF, 717KB)
Table 3: Minimum Geotechnical Investigations and Reporting Requirements for Resource Consents for Urban Residential Scale Development (Option 2)
| Table 3: Minimum Geotechnical Investigations and Reporting Requirements for Resource Consents for Urban Residential Scale Development (Option 2) |
| Development Scenario |
Minimum Geotechnical Testing Required |
Minimum Reporting Requirements |
|
Urban residential development
(typically 15-60 households per ha)
eg home in a new subdivision
Commercial or industrial development
eg a warehouse building in an industrial park
|
Deep ground investigation carried out by a geotechnical engineer* to further categorise liquefaction vulnerability and to determine mitigation options (where applicable)
|
- Detailed assessment completed in accordance with MBIE / MfE guidance
- Deep ground investigations eg Cone Penetration Tests (CPT) in accordance with Table 3.3 of“Planning and engineering guidance for potentially liquefaction-prone land” guidance from MBIE / MfE
- Recommendations for locations of future buildings and infrastructure
- Recommendations for foundations of future buildings
- Where liquefaction category for the site is assumed or confirmed to be high – recommendations for mitigation eg ground improvement
|
Notes:
* Geotechnical engineer means Chartered Professional Geotechnical Engineer or Professional Engineering Geologists (PEngGeol) in the practice field of geotechnical. Where the testing and reporting is carried out by a structural engineer, the guidance of a geotechnical engineer should be sought in accordance with “Geotechnical Input Decision Chart for Structural Engineers” from Engineering New Zealand.
Building on land where Liquefaction Vulnerability has been determined at Resource Consents stage
Where the liquefaction vulnerability has been adequately categorised at resource consent stage, the following will be required at building consent stage:
- If the proposed building work is within the building platform identified at resource consent stage, submit a ground bearing report (in accordance with NZS 3604) and a copy of the liquefaction report (from the resource consent).
- If the proposed building work isn’t within the building platform identified at resource consent stage, submit a ground bearing report (in accordance with NZS 3604), which includes confirmation that the soil profile is what is anticipated for the liquefaction vulnerability category identified at resource consent stage. Confirmation that the foundation design is in accordance with recommendations in the liquefaction report is also required, along with a copy of the liquefaction report.
NOTE: Further geotechnical investigation may be required if the on-site observations don’t align with the liquefaction assessment report, if there is a known geotechnical risk or if the liquefaction vulnerability category is high.
Exceptions to the requirement to provide a liquefaction assessment
The following exceptions to the requirement to provide a liquefaction assessment apply:
- Buildings being built in a yard for relocation to another site
- Non-habitable sheds / garages up to 100m2 or where Specific Engineering Design (SED) to Ultimate Limit State (ULS) for a 1/100 year event
- Pole sheds constructed in an area that is zoned rural or where SED to ULS for a 1/100 year event
- Pole sheds up to 100m2 in an area that is zoned as commercial, industrial, residential or greenbelt residential or where SED to ULS for a 1/100 year event
- Habitable outbuildings such as sleepouts with a maximum floor area of 30m2
- Extensions to the ground floor area of existing buildings where the proposed floor area of the extension is less than 50m2.
- Boundary adjustments where there is no net increase in the number of lots AND no changes to infrastructure
- Lots not intended to be built on or to contain infrastructure e.g. land set aside for private reserves or to be vested as open space reserves.
The limitations to these exceptions are:
- Where the liquefaction category for the property is identified as high risk (in which case the MBIE Canterbury guidance applies)
- If there is a consent notice on the property title requiring that geotechnical investigation is carried out for all new buildings
- Where a proposed extension to an existing building includes the creation or extension of a 2nd or subsequent storey
- Where there is a known geological risk.