Importance Level 3 (IL3)

Overview

Importance Level 3 applies to buildings or structures designed to hold large numbers of people or that support critical public infrastructure. These require enhanced engineering considerations due to increased risk in the event of failure.

Why this is important

Structures at IL3 require higher wind speed ratings and stricter design criteria
Reduces risk in high-occupancy, high-impact facilities
Supports compliance with the National Construction Code (NCC 2019 – Volume 1)
Helps engineers and franchise users determine if special approvals or costs apply

Examples of Importance Level 3 buildings

According to Section B1.2 of the NCC 2019 Guide to Volume 1, examples include:

Buildings where more than 300 people can congregate in one area
Primary, secondary schools, or day care facilities with capacity greater than 250
Colleges or adult education facilities with capacity over 500
Health care facilities with 50+ residents (but without surgery/emergency treatment)
Jails and detention centres
Facilities with occupant loads over 5000
Power generation, water, or wastewater treatment plants not classified under IL4
Facilities that contain hazardous materials capable of causing harm (but not extending beyond the property boundary)

Engineering considerations

Regional wind speeds may range from 46 m/s (165.6 kph) to 85 m/s (306.0 kph)
These structures may require advanced engineering approval and longer lead times
Misclassification may result in compliance issues or costly revisions

🛈 This information is valid until September 2022. Clients should always refer to the latest version of the NCC.