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Building Classifications

Building Classifications

We hear it from our customers everyday, trying to wrap your head around all the different aspects involved in determing what is required on any project can be tedious. Different building classifications in New Zealand and Australia all have an effect on their seismic code requirements. Whether you are trying to gain better understanding of how seismic requirements are determined, or just trying to complete what is required on a given project Vaico can help.

If you are unsure of what Seismic Design Category (SDC) your project may fall under it can typically be found in the structural notes section of your construction drawings, or they may also be listed in the project specification. If you are still having trouble determining what category it falls under, Vaico has staff available that can walk you through your project details and determine your seismic building code requirements.

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The classification of building parts (Table 4) is a key step in the determination of the seismic actions, in accordance with NZS 1170.5:2004 section 8.
Traditionally, ceiling systems have been classified under P7 – All other parts, with the exception of those ceilings installed in buildings of importance level 4 or greater.
Currently, most light suspended ceilings are classified as P7 – which only requires design for serviceability, for an SLS1 earthquake.
Table 8.1 of NZS 1170.5:2004 does not explicitly define the various ceiling systems likely to be installed in the buildings. Rather, it provides risk criteria, a risk factor (Rp) and a limit state for design. Fundamentally, although not explicitly defined, the underlying risk for ceiling systems lies in both mass and height above personnel. With this in mind, it is recommended that any light suspended ceiling that provides support to P4 components (for example, emergency lights, exit signs, smoke/fire detectors, fire sounders/evacuation speakers and sprinklers connected via proprietary flexible droppers) or is above escape routes (a continuous unobstructed route from any occupied space to a final exit) must be classified as P4 and designed for ULS.

Table 4: Classification of building parts.

Limit State
P1Part representing a hazard to life outside the structurePart weighing more than 10 kg and able to fall more than 3 metres onto a publicly accessible areaULS
P2Part representing a hazard to a crowd of greater than 100 people within the
Part weighing more than 10 kg and able to fall more than 3 metres onto a publicly accessible areaULS
P3Part representing a hazard to individual life within the structurePart weighing more than 10 kg and able to fall more than 3 metres onto a publicly accessible areaULS
P4Part necessary for the continuing function of the evacuation and life safety systems within the structureULS
P5Part required for the operational continuity of the structureOnly parts essential to the operational continuity of structures with importance level 4 will be classified as P5 – non-essential parts and parts within structures of other importance levels will be otherwise classifiedSLS2
P6Part for which the consequential damage caused by its failure is disproportionately greatSLS1
P7All other partsSLS1


B1/VM1 (which references AS/NZS 1170.0:2002 Appendix 2) defines building importance levels as shown in Table 5 below. The building importance level (IL) shall be nominated on the design documentation.

Table 5: Building importance levels.

Table 5: Building importance levels.Description of building typeSpecific structure
1Buildings posing low risk to human life or the environment or a low economic cost should the building fail. These are typically small non-habitable buildings, such as sheds, barns and the like that are not normally occupied, though they may have occupants from time to time.

  • Ancillary buildings not for human habitation

  • Minor storage facilities

  • Backcountry huts

2Buildings posing normal risk to human life or the environment or a normal economic cost, should the building fail. These are typical residential, commercial and industrial buildings.

  • All buildings and facilities except those listed in importance levels 1, 3, 4, and 5

3Buildings of a higher level of societal benefit or importance or with higher levels of risk significant factors to building
occupants. These buildings have increased performance requirements because they may house large numbers of
people, vulnerable populations or occupants with other risk factors or fulfil a role of increased importance to the local community or to society in general.

  • Buildings where more than 300 people congregate in 1 area

  • Buildings with primary school, secondary school, or daycare facilities with a capacity greater than 250

  • Buildings with tertiary or adult education facilities with a capacity greater than 500

  • Health care facilities with a capacity of 50 or more residents but not having surgery or emergency treatment facilities

  • Jails and detention facilities

  • Any other building with a capacity of 5,000 or more people

  • Buildings for power generating facilities, water treatment for potable water, wastewater treatment facilities, and other public utilities facilities not included in importance level 4

  • Buildings not included in importance level 4 or 5 containing sufficient quantities of highly toxic gas or explosive materials capable of causing acutely hazardous conditions that do not extend beyond property boundaries

4Buildings that are essential to post-disaster recovery or
associated with hazardous facilities.

  • Hospitals and other health care facilities having surgery or emergency treatment facilities

  • Fire, rescue, and police stations and emergency vehicle garages

  • Buildings intended to be used as emergency shelters

  • Buildings intended by the owner to contribute to emergency preparedness, or to be used for communication, and operation centres in an emergency, and other facilities required for emergency response

  • Power generating stations and other utilities required as emergency backup facilities for importance level 3 structures

  • Buildings housing highly toxic gas or explosive materials capable of causing acutely hazardous conditions that extend beyond property boundaries

  • Aviation control towers, air traffic control centres, and emergency aircraft hangars

  • Buildings having critical national defense functions

  • Water treatment facilities required to maintain water pressure for fire suppression

  • Ancillary buildings (including, but not limited to, communication towers, fuel storage tanks or other structures housing or supporting water or other fire suppression material or equipment) required for operation of importance level 4 structures during an emergency

5Buildings whose failure poses catastrophic risk to a large area (e.g. 100 km2) or a large number of people (e.g. 100,000).

  • Major dams

  • Extremely hazardous facilities

What does “designed to the Building Code” mean?

Achievement of 100% compliance is regarded as the embodiment of good practice, but it is in fact the absolute minimum acceptable standard. This could be informally addressed by engineers discussing alternatives with their clients, but in the past this has met with resistance, mostly over misunderstood cost perceptions. A better client education process, with more explanation in the Building Code is needed. This is where the experience of Vaico and the ISAT partnership is unmatched in New Zealand and across the globe.

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