What is Incidental Use?

MeyerFire University | LS101.06

​By Chris Campbell, PE

RESOURCES

• One-Page Summary [PDF]
• Notes Page [PDF]

CODE & STANDARD REFERENCES

• IBC – 2021: Table 509.1 List of Incidental Use Areas

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TRANSCRIPT

What is an Incidental Use? 

DEFINITION IN THE IBC

Many buildings contain rooms or spaces that are related to the primary occupancy but may pose a higher level of fire or life safety risk than the occupancy itself.   

The IBC classifies these spaces as Incidental Uses in Section 509.1. While “incidental use” is not formally defined in IBC Chapter 2, Section 509.1 describes Incidental Uses as “ancillary functions associated with a given occupancy that generally pose a greater level of risk to that occupancy and are limited to those uses specified in Table 509.1.” 

COMMON EXAMPLES

Common examples of incidental uses include furnace or boiler rooms, laboratories that are present within other occupancies, large laundry rooms and trash collection rooms. 

In general, there are an almost unlimited number of building uses, but Incidental Uses are limited to those found in IBC Table 509.1.  

For projects where NFPA 101 is applicable, note that Incidental Use is defined differently in the Life Safety Code, which we’ll cover in a different video. 

The concept of incidental use is important – since these spaces contain greater hazards or pose a greater level of risk, there are additional protection requirements beyond those associated with the main occupancy in which they are located. 

REQUIREMENTS FOR INCIDENTAL USE

The primary code requirements associated with incidental uses are fire-resistance rated construction and sprinkler protection.

When an incidental use requires a rated separation, the rating must be provided by fire barriers, horizontal assemblies, or both.  

Additionally, the supporting construction must be greater than or equal to the rating required for the incidental use. So if your incidental use is located on Level 2 of your building and requires a rated separation, all of the structural members supporting those the fire barriers and horizontal assemblies associated with the incidental use must also be rated. 

There is an exception for Types IIB, IIIB and VB construction, where supporting construction for 1-hour fire barriers and horizontal assemblies associated with incidental uses is not required to be rated (unless otherwise required by another Section).  Note that in Type IV-B and IV-C construction, any required rated separations for incidental uses must be provided with a gypsum board cover.   

In my experience, incidental use requirements are easy to overlook when reviewing a design for building code compliance, particularly when IBC Table 509.1 requires a fire resistance-rated separation. As part of any code review or code compliance process, it’s a good idea to check Table 509.1 to confirm if any incidental uses are present in your building. 

I have also seen building designers misunderstand the concept of incidental use, believing that an incidental use should be considered a distinct occupancy classification.  While incidental uses do come with additional requirements beyond those associated with any IBC occupancy classification, For example, take a 200 SF storage room located within the emergency department of a hospital. This room would require a 1-hour fire resistance rated separation per IBC Table 509.1, but it is still considered part of the Group I-2 occupancy classification for the hospital. 

LIMITED TO 10% OF THE BUILDING STORY

Incidental uses are limited to 10% of the building area of the story in which they are located and should be included in the building occupancy in which they are located. If the incidental use exceeds 10% of the floor area of the story, it would need to be classified as its own occupancy. 

Finally, if an incidental use requires sprinkler protection and the building is not otherwise sprinkler-protected, the sprinkler system is only required within the incidental use itself. 

SUMMARY

So what is an incidental use? 

It’s an ancillary space that generally poses a higher level of risk than the occupancy in which its located. Incidental uses are limited to the list found in IBC Table 509.1 and generally required with a 1 hour fire resistance rated separation and/or sprinkler protection.

I’m Chris Campbell, this is MeyerFire University.