Natural hazard determinations involving inundation

Posted: 29 March 2018

MBIE issued three determinations in 2017 relating to natural hazards. This article looks at some of the common issues that arise about inundation.

The Building Act states that, except in certain circumstances, a building consent authority (BCA) must refuse to grant a building consent for a new building or major alteration if:

  • the land is subject to one or more natural hazards; or
  • the building work is likely to accelerate, worsen or result in a natural hazard.

The natural hazard provisions apply only to major alterations or the construction of new buildings. The Building Act does not define ‘major alteration’ but determinations have identified some useful criteria for deciding what constitutes a major alteration.

Determination 2017/055 has more detail. 

The Act identifies the natural hazards, such as erosion and subsidence, but doesn’t state the level of an event to which the natural hazard provisions of the Act apply. 

In general, land is considered subject to a natural hazard when the hazard is more than minimal or trivial. Previous determinations have established, for example, a 1 per cent Annual Exceedance Probability rainfall event (commonly referred to as a 100-year flood event) is an appropriate level when considering inundation caused by rainfall and surface water flow.  

Section 71(2) allows BCAs to grant building consents for new buildings or major alterations on land subject to a natural hazard, subject to the BCA being satisfied that there is adequate provision made to:

  • “(a) protect the land, building work, or other property [where relevant] from the natural hazard …; or
  • (b) restore any damage to that land or other property as a result of the building work.”

These conditions give rise to certain questions. For example, is it only the building work that needs to be protected? However, the Court of Appeal interpreted 71(2)(a) as requiring the protection of land and the building work, and (where relevant) other property. Restoration may be required in some cases.

The Court of Appeal and determinations have concluded ‘adequate provision to protect the land’ means providing an adequate level of protection but does not mean eliminating the natural hazard. The level of protection required is a question of degree and a BCA is expected to take a common-sense approach. 

For example, in relation to inundation, determining the level of protection required to satisfy section 71(2) should take into account factors such as maximum depth, velocity, frequency of occurrence, and likely effects on the land. The level of protection required for land is likely to be less than for protecting buildings (unless there is significant risk of erosion causing loss of support for the building). 

Determinations have also considered what ‘adequate provision to protect the building work’ means, concluding that achieving compliance with the Building Code will meet this requirement. 

While these determinations are case-specific, the analysis of the natural hazard provisions included in the determinations provides useful guidance for other similar circumstances. 

Inundation determinations:

This information is published by the Ministry of Business, Innovation and Employment’s Chief Executive. It is a general guide only and, if used, does not relieve any person of the obligation to consider any matter to which the information relates according to the circumstances of the particular case. Expert advice may be required in specific circumstances. Where this information relates to assisting people: