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.

Sprinkler Requirements in New Code

A flexible expansion of fire sprinkler protections in apartment buildings and an update to 2006 model building and fire codes are features of Wisconsin commercial building and fire codes changes adopted November 7, 2007, by the state Department of Commerce. After several years of development, with input from people throughout Wisconsin and review by the legislature, changes to Comm 60-66, Commercial Building Code, and Comm 14, Fire Prevention Code, are expected to go into effect on March 1, 2008.

For new construction, a significant increase in the multifamily buildings provided with fire sprinklers was modified by phasing in the new fire sprinkler protection. The phase-in will provide sprinkler installation in 2008 for new construction of multifamily buildings of more than eight units, and will be lowered in 2011 to new multifamily dwellings of three or more units. (See Section 68 in adopted draft for phase-in.)

The new rules will provide adjusted sprinkler coverage for three- and four-unit dwellings not served by municipal water systems or private community wells. Such buildings will be able to have systems conforming with NFPA 13D, a standard for dwellings that allows lower water usage while protecting lives from fire. (See Table 62.0903 and following and Section 74 in adopted draft.)

Sprinkler protection changes will not affect existing buildings or new one- and two-family homes.

Existing buildings coverted to residential use may require sprinkler protection. Building construction plan submittals made before the code change effective date to the Department of Commerce or delegated plan review municipalities will be reviewed under the old/current code.

Submittals after the effective date will use the new code provisions, with a few vital exceptions dealing with initiated, ongoing projects. (See Sections 29m, 30, and 30m in adopted draft for extensions of review.)

New printed copies of the Wisconsin commercial building and fire prevention codes are expected to be available from state Document Sales in February. The 2006 versions of the adopted national model codes can be obtained from the International Code Council, http://www.iccsafe.org/ and the National Fire Protection Association, http://www.nfpa.org/, respectively.

There will not be a new "Enrolled Code," which has been a printed combination of the Wisconsin and model building codes. Instead, the Safety and Buildings Division will put code insert pages on the Internet in early 2008. The pages will be designed to fit Wisconsin code provisions into the loose leaf versions of adopted model codes.

The adopted draft of the code changes is available on Commerce's Safety and Buildings Division Website.People wishing to follow the process of bringing the code changes into fruition can become part of the S&B commercial buildings, fire prevention, or fire protection email groups, http://commerce.wi.gov/SB/SB-DivEmailSignup.html.

This update was originally posted on the Wisconsin Safety & Buildings website.