Site Analysis

Understanding all the features of a site, using and protecting the best, and minimising the impact of the worst.

Hazards

Potential hazards may be the result of human activity, such as contamination and pollution, and natural hazards, such as storms, floods, earthquakes, geothermal activity, landslides and erosion, tsunamis and rising sea levels.

For each type of hazard, consider:

  • Has it happened in the past?
  • Could it happen on this site?
  • What is the chance of it happening in future?
  • How much harm or damage could it cause?
  • Does the risk associated with the hazard require further action?

New Zealand Building Code

The New Zealand Building Code is concerned with the health and safety of building occupants. It requires that, in the event of a hazard, occupants must be able to evacuate the building safely, but does not require that, after a major hazard such as an earthquake, a building will remain structurally sound. A specific requirement to do so is likely to require a design in excess of NZBC requirements.

Building Act restrictions

Under Section 71 of the Building Act, building consent authorities must refuse to grant a building consent for construction of a building (or major alterations to a building) 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 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 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.

Where a land title has this note on it, the Earthquake Commission 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.

Microclimate hazards

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, construction requires specific engineering design (SED).

Fire risk

Wildfires are a growing risk on the edges of towns and cities and towns where forests or scrub and homes are in close proximity.

In the Port Hills wildfires of February 2017 nine homes were completely lost and five others damaged. At least 450 households with an estimated 1,400 people had to leave their homes during the fires and 1,650 hectares of land were burnt. Insurance payouts cost $17.7 million, and the total cost has been estimated at over $30 million.

Early 2019 saw serious fires close to Wakefield in the South Island.

Climate change hazards

Because houses built today will have a life of more than 50 years, homeowners and designers must consider climate changes likely to affect a site in coming decades. These may involve rising sea levels for coastal property, more frequent floods for low-lying areas, or higher temperatures in some regions.

While most people think of earthquake damage when they think of Earthquake Commission (EQC) payouts, in fact EQC has paid out on 15,196 weather-related claims in the years 20002017. The total was $450 million, with approximately one third of that for damage to buildings. Work published by Motu Economic and Public Policy Research in early 2020 indicates that more extreme weather events brought by climate change are likely to increase costs for EQC by 925%.

 

Updated: 06 March 2020