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9 Building Importance Category

9.1 Definition

It is not always possible to avoid building within a fault avoidance zone. Past land development decisions may have resulted in buildings being within a fault avoidance zone, or have given people an expectation that they are able to build there now. In addition, where the level of certainty is low regarding the fault location, its complexity and recurrence interval, it may be difficult to justify placing limits on any building in these areas.

Buildings within a fault avoidance zone, particularly buildings crossing active faults, are very likely to be damaged in a fault rupture. A Building Importance Category states the relative importance of assessing the suitability of a building within, or proposed for, a fault avoidance zone.

The categories are based on risk levels for building collapse according to the building type, use and occupancy. Category one is the least important; category four is most important.

Councils can use Building Importance Categories to make decisions about resource consents (section 11 of this document), and to require conditions on buildings within fault avoidance zones.

There are four Building Importance Categories, and one sub-category:

Category 1: Structures presenting a low degree of hazard to life or property.

Examples:

  • Structure with a total floor area less than thirty square metres
  • Farm buildings
  • Isolated structures
  • Towers in rural situations
  • Fences
  • Walls
  • In-ground swimming pools.

Category 2a: Residential timber-framed construction

Examples:

  • Timber-framed single-storey buildings.

Category 2b: Normal structures and structures not in other categories.

Examples:

  • timber framed houses with a floor area of more than 300 square metres
  • houses outside the scope of NZS: 3604 Timber Framed Buildings
  • multi-occupancy residential, commercial (including shops), industrial, office and retailing buildings designed to accommodate less than 5000 people and also those less than 10,000 square metres gross area
  • public assembly buildings, theatres or cinemas with a floor space of less than 1000 square metres
  • car parking buildings.

Category 3: Structures that, as a whole, may contain people in crowds or have contents of high value to the community, or pose a risk to large numbers of people in close proximity.

Examples

  • Emergency medical and other emergency facilities not designated as post-disaster facilities
  • Buildings where more than 300 people can congregate in one area
  • Buildings and facilities with primary school, secondary school or day care facilities with a capacity greater than 250 people
  • Buildings and facilities with greater than 500 for colleges or adult education facilities
  • Health care facilities with a capacity of 50 or more residents but not having surgery or emergency treatments facilities
  • Airport terminals, principal railway stations, or other transport terminals with a capacity greater than 250 people
  • Any occupancy with a capacity greater than 500 people
  • Power generation facilities, water treatment and waste treatment facilities and other public utilities not included in Importance Category 4
  • Buildings and facilities not included in Importance Category 4, containing hazardous materials capable of causing a hazard or hazardous conditions that do not extend beyond the boundaries of the property on which they are located.

Category 4: Structures with special post-disaster functions.

Examples:

  • Buildings and facilities designated as essential facilities
  • Buildings and facilities with special post-disaster functions
  • Medical emergency or surgical facilities
  • Emergency service facilities such as fire stations, police stations and emergency service vehicle garages
  • Utilities required as backup for buildings and facilities of Importance Category 4
  • Designated emergency shelters, emergency centres and ancillary facilities
  • Buildings and facilities containing hazardous materials capable of causing a hazard, or hazardous conditions, beyond the site on which they are located.

The relationship between the fault recurrence interval and Building Importance Category in previously subdivided or developed areas, and in greenfield sites are as follows:

  • For Fault Recurrence Interval class I areas (recurrences up to 2,000 years), Building Importance Class 1 buildings are allowable in both developed (including previously subdivided) and greenfield areas.
  • For Fault Recurrence Interval class II areas (recurrences between 2,000 years and up to 3,500 years),Building Importance Class 1and 2a buildings are allowable in developed (including previously subdivided) areas, but only Building Importance Class 1 buildings are allowable in greenfield areas.
  • or Fault Recurrence Interval class III areas (recurrences between 3,500 years and up to 5,000 years),Building Importance Class 12a and 2b buildings are allowable in developed (including previously subdivided) areas, but only BuildingImportance Class 1 and 2a buildings are allowable in greenfield areas.
  • For Fault Recurrence Interval class IV areas (recurrences between 5,000 years and up to 10,000 years),Building Importance Class 12a2b and buildings are allowable in developed (including previously subdivided) areas, but only Building Importance Class 1, 2a and 2b buildings are allowable in greenfield areas.
  • For Fault Recurrence Interval class V areas (recurrences between 10,000 years and up to 20,000 years),Building Importance Class 12a2b and buildings are allowable in developed (including previously subdivided) areas and greenfield areas.
  • For Fault Recurrence Interval class VI areas (recurrences between 20,000 years and up to 120,000 years), ALL Building Importance Classes are allowable in developed (including previously subdivided) areas and greenfield areas.

Note: Faults with recurrence intervals of greater than 125,000 years are not considered to be active.