#101Wednesdays: When is an "incidental use" incidental?

Blog Post created by gharrington Employee on Sep 27, 2017

When should a portion of a building should be treated as an incidental use or as its own occupancy?


A topic that sometimes prompts a bit of animated discussion when I teach NFPA’s three-day Life Safety Code Essentials seminar is incidental uses. It is not always clear when a portion of a building should be treated as an incidental use or as its own occupancy. In today’s #101Wednesdays post, I will attempt to provide some guidance.

Before getting into the NFPA 101 requirements, it’s important to recognize we live in a world in which the Life Safety Code co-exists with building codes. In most cases, the building code is the International Building Code (IBC), which is promulgated by the International Code Council. Both the IBC and NFPA 101 use the term incidental; however, the term has different meanings in each code. In NFPA 101, incidental refers to “minor” uses that are accessory to and/or support the predominant occupancy and do not warrant their own occupancy classification. This concept in the IBC is known as accessory occupancies. In the IBC, the term incidental uses refers to what NFPA 101 calls hazardous areas. The concepts are very similar, but the terminology is different. Be sure to understand how each term is used in each code so you’re not comparing apples to oranges.

Classification of occupancy is addressed by Chapter 6 of NFPA 101, and it is based on how a building is used. The Code’s requirements are predicated on occupancy classification, which directly relates to occupant characteristics and their associated risks. It is common for buildings to be comprised of more than occupancy; these are known as multiple-occupancy buildings (see 6.1.14 of NFPA 101, 2015 edition). Multiple occupancies are then treated as either mixed multiple occupancies ( or separated multiple occupancies ( In each case, the requirements applicable to all involved occupancies must be evaluated. However, permits some, but not all uses to be considered incidental. For example, where an office building (business use) has an office supply closet (storage use), the AHJ is permitted to judge the storage use to be incidental to the predominant business use and classify the building as a business occupancy, not a multiple occupancy (business and storage). The requirements of Chapter 38 (new business) or 39 (existing business) apply, as applicable, and the AHJ ignores the storage occupancy requirements of Chapter 42. If that same office building has a cafeteria with an occupant load of 50 or more, however, that is an assembly occupancy, and the building must be treated as a multiple-occupancy building (business and assembly). Here is how it works:

Certain uses that are permitted to be considered incidental subject to the determination of the AHJ are specified by mercantile, business, industrial, and storage uses. Examples of each might include:


  • Incidental mercantile: newsstand in an office building lobby (business occupancy)
  • Incidental business: supervisor’s office in a distribution warehouse (storage occupancy)
  • Incidental industrial: repair shop in a bicycle store (mercantile occupancy)
  • Incidental storage: raw materials storage in a manufacturing plant (industrial occupancy)


For these uses, no measurable threshold in terms of area or occupant load applies. Whether one of these uses is incidental or its own occupancy is strictly up to the AHJ. This requires sound, reasonable judgment.


Other nonresidential uses having an occupant load fewer than that established by each occupancy classification’s definition are also considered incidental. Determining whether these areas are incidental requires no judgment. The occupant load based on how the area is used is determined, and if the occupant load is less than that established by the occupancy’s definition, it’s incidental. Examples of these might include:


  • Incidental assembly: café with an occupant load of fewer than 50 in a book store (mercantile occupancy)
  • Incidental educational: tutoring for fewer than four students through the twelfth grade in an office building (business occupancy)
  • Incidental day care: child care service for fewer than four kids at a health club (assembly occupancy)
  • Incidental health care: limited skilled nursing care for fewer than four patients in an assisted living facility (residential board and care occupancy)
  • Incidental ambulatory health care: oral surgery and recovery provided to fewer than four patients in a dentist’s office (business occupancy)


Note that residential uses (one- and two-family dwellings, lodging or rooming houses, hotels and dormitories, apartment buildings, and residential board and care) can never be considered incidental. This is to ensure that the requisite protection for sleeping occupants, namely smoke alarms, is always provided. An on-call physicians’ sleeping room in a hospital is NOT incidental; rather, it’s usually a lodging or rooming house occupancy, and the requirements of Chapter 26 apply in addition to the requirements of Chapter 18 or 19 for health care occupancies. Also be aware that even though an area is incidental, it might still need to be protected as a hazardous area by automatic sprinklers, 1-hour separation, or both (e.g., a soiled linen storage room in a hospital).

It’s interesting to note that the IBC takes a different approach to accessory occupancies. The IBC states that occupancies can be considered accessory if they are ancillary to the main occupancy of the building and do not exceed 10 percent of the floor area of the story in which they are located and do not exceed the allowable area for nonsprinklered buildings for each accessory occupancy. For example, in a 500,000 ft2 building used predominantly as a warehouse, up to 10 percent of the area (50,000 ft2) could be used for offices (assuming Type I construction), and the office area could be considered an accessory occupancy subject only to the requirements applicable to the storage use. To me and to the Safety to Life Technical Committees, 50,000 ft2 of offices is a lot of business use area to treat as accessory (IBC) or incidental (NFPA 101). This is not to disparage the IBC; it’s only to point out the different protection philosophies provided by each code.

I hope this overview of incidental uses in the Life Safety Code has been useful. Thanks for reading, and until next time, stay safe!

Got an idea for a topic for a future #101Wednesdays? Post it in the comments below – I’d love to hear your suggestions! Follow me on Twitter: @NFPAGregH

Did you know NFPA 101 is available to review online for free? Head over to and click on “Free access to the 2015 edition of NFPA 101.”


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