The Building Act has rules around whether or not building or renovation work should get a building consent when the house is in an area subject to natural hazards.
Under Section 71 of the Building Act, building consent authorities must refuse to grant a building consent for building work (including alterations that require consent) if:
- the land is subject or is likely to be subject to 1 or more natural hazards (erosion, falling debris, subsidence, inundation [flooding] or slippage); or
- building work is likely to accelerate, worsen, or result in a natural hazard on that land or any other property.
BCAs can, however, issue consent if they are satisfied that there is adequate provision:
- to protect the land, building work, or other property from the natural hazard or hazards; or
- to restore any damage to that land or other property as a result of the building work.
BCAs must issue a consent for building or renovations on land subject to natural hazards if they consider that the work will not worsen the hazard and they believe it is reasonable to grant a waiver or modification of the Building Code for the natural hazard concerned (Section 72).
If consent is given for building work on land subject to natural hazard, a note will be added to the certificate of title that a building consent was granted under Section 72, identifying the natural hazard concerned.
- The building consent authority is exempted from liability for damage arising from the natural hazard.
- The Earthquake Commission (Toka Tū Ake EQC) can legally decline to provide cover, depending on the nature of the hazard.
- Insurance companies may decline to offer cover or may exclude cover for the relevant hazard.
Local authorities and insurers are carrying out a lot of work around likely future impacts of climate change. The impacts will be most strongly felt by homeowners whose properties are very close to the sea or in very low-lying areas.
In New Zealand, climate change is forecast to result in rising sea levels, stronger/more frequent storms and more extreme rainfall, bringing severe flooding.
A major assessment of climate change released in 2021 by the IPCC (the UN’s Intergovernmental Panel on Climate Change) forecasts large rises in sea level.
Under the best of 5 possible scenarios, where governments around the world quickly agree to make substantial reductions in emissions, the global mean sea level is forecast to rise by one third to half a metre over the next 90 years. Under the worst scenario, where there are few reductions made in greenhouse gas emissions, a sea level rise of up to around one metre in 90 years is forecast, with the note that an increase as much as 2 metres “cannot be ruled out”. The IPCC report was approved by representatives of 195 national governments and is regarded as conservative.
Recently-reported regional measurements lend support to the forecasts. In Lyttelton Harbour, the average rise in sea level over the first 60 years of last century was 1.3 mm/year; in the last 15 years, it has averaged 7 mm/year.
Some house insurers are changing how they calculate premiums. Houses at greater risk for disasters such as floods caused by rising sea levels and extreme weather events are attracting higher premiums.
Research published in 2020 found that some coastal homes in Wellington and Christchurch will find it difficult or impossible to get house insurance from 2030, with homes in similarly exposed locations in Auckland and Dunedin following only a few years later. In these four cities, at least 10,000 properties may be uninsurable by 2050.
Many councils are creating resources and tools to help with planning around flooding and sea level rise. Waikato Regional Council, for example, has created an online Coastal inundation tool that helps give a general indication of the areas that may be at risk. Greater Wellington Regional Council has also produced a website with a dynamic map of areas likely to be affected by sea level rise. Northland Regional Council has maps of areas at risk of coastal flooding and coastal erosion.
On some sites there may be hazardous microclimates that may lead to problems such as rapid corrosion of metal fasteners and fixings. As an example, the scope of NZS 3604 Timber-framed buildings specifically excludes:
- Industrial contamination and corrosive atmospheres
- Contamination from agricultural chemicals or fertilisers
- Geothermal hot spots – areas within 50 m of a bore, mud pool, steam vent, or other source.
In these circumstances, building and renovation work requires specific engineering design.