Level of importance

Clause A3 of the Building Code defines the significance of a building by its importance level (IL), which is related to the consequences of failure. There are five levels of importance, considered by the importance of the building to society: 

  • Level 1: Structures presenting a low degree of hazard to life or property, such as walkways, outbuildings, fences and walls.
  • Level 2: Normal structures and structures not covered by other categories, such as timber-framed houses, car parking buildings or office buildings.
  • Level 3: Structures that may contain crowds, have contents of high value to the community or pose a risk to large numbers of people in close proximity, such as conference centres, stadiums and airport terminals.
  • Level 4: Buildings that must be operational immediately after an earthquake or other disastrous event, such as emergency shelters and hospital operating theatres, triage centres and other critical post-disaster infrastructure.
  • Level 5: Structures whose failure poses a catastrophic risk to a large area or a large number of people, such as dams, nuclear facilities or biological containment centres.

The required level of seismic performance increases with each level of importance. In general, important structures, such as hospitals, communications centres and those that provide occupation for many people, are designed for a greater level of earthquake shaking than ordinary commercial structures.