Occupancy Category - What is it?

In determining the code compliance and structural requirements of one of our building design projects, one of the key steps is to calculate the required loads. The load requirements are normally contained in the applicable building code for the project, if there is one.

The occupancy category is simply a number, Roman Numeral I, II, III, or IV, and it affects the load requirement by adjusting the importance factor for the building in relationship to the risk to human life that would exist in the event of the failure AND the importance of avoiding a failure in an emergency due to the nature of the building's function in the event of an emergency. The higher the occupancy category number, the higher the importance of avoiding failure and keeping the building functioning in the event of an emergency.

Determining the correct Occupancy Category at the beginning of your design project using the same criteria that your design professional will allow the project to be analyzed for the correct loads right off the bat and ensure that the design will be efficient and sound for the nature of the building's use throughout the life of the structure.

For certain projects that do not require a building code to be applied, our practice at Halberg Engineering is to apply the normal building design loads for a commercial structure, but to use the lowest Occupancy Category that fits the intended use of the building. This allows the building to be designed to a current standard but also to allow the design loads to be reduced in accordance with the risk to life and property as appropriate for each project.

From Chapter 16 of the International Building Code, the Occupancy Category explanations are shown below. As always, if you have any questions about this information, be sure to contact your design professional as early in the design process as possible!

OCCUPANCY CATEGORY OF BUILDINGS AND OTHER STRUCTURES (from IBC Table 1604.5)

I - Buildings and other structures that represent a low hazard to human life in the event of failure:
Agricultural facilities. Certain temporary facilities. Minor storage facilities.

II - Buildings and other structures except those listed in Occupancy Categories I, III and IV

III - Buildings and other structures that represent a substantial hazard to human life in the event of failure. A few examples include:
Covered structures whose primary occupancy is public assembly with an occupant load greater than 300. Buildings and other structures with elementary school, secondary school or day care facilities with an occupant load greater than 250. Health care facilities with an occupant load of 50 or more resident patients, but not having surgery or emergency treatment
facilities. Jails and detention facilities.

IV - Buildings and other structures designated as essential facilities. A few examples include:
Hospitals and other health care facilities having surgery or emergency treatment facilities. Fire, rescue and police stations and emergency vehicle garages. Designated earthquake, hurricane or other emergency shelters. Buildings and other structures having critical national defense functions.