Importance Level 4 (IL4)

Overview

Importance Level 4 buildings are considered essential facilities in the event of a disaster or emergency. These structures are either vital for post-disaster recovery or involve hazardous conditions that pose risks beyond the property boundary.

They require the highest engineering standards to reduce risk and maintain critical operations.

Why this is important

IL4 structures support public safety and disaster response
Failure of these buildings can have widespread impact
NCC 2019 mandates stricter engineering for IL4 structures
Ensures buildings are disaster-resilient and compliant with national standards

Examples of Importance Level 4 buildings

Essential facilities (e.g. only hospital in a region)
Medical emergency oral surgery facilities
Emergency service buildings:
- Fire stations
- Police stations
- Rescue facilities
- Emergency vehicle garages
Designated emergency shelters and centres
Utilities used as backup for IL4 buildings
Facilities containing hazardous materials capable of causing conditions beyond the property boundary

🛈 A hospital may be classified as IL4 if it’s the only one in the area. If there are several, it may only be IL3.

Engineering considerations

Regional wind speed range: 48 m/s (172.8 kph) to 90 m/s (324.0 kph)
May require advanced structural modelling, materials, and approvals
IL4 often triggers additional local council and code compliance requirements

Determining Importance Level

A general method for determining the Importance Level of any building is to assess the hazard to human life and the impact on the public if the building fails.

Tips & best practices

Always ask if the building will be used during an emergency
Check if the site contains hazardous materials or serves as a critical utility
When in doubt, escalate to Engineering using the Site Check form
Refer to NCC Volume 1 (2019) for additional criteria

This information is provided as a guide only and is valid until September 2022. Clients should confirm details with the provisions of the National Construction Code (NCC 2019 – Volume 1).