What is an Assembly Occupancy?

MeyerFire University | LS101.09

By Chris Campbell, PE

RESOURCES

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

CODE & STANDARD REFERENCES

• IBC – 2021: Section 303.1 – Definition of Assembly Occupancy, with Groups
  
• IBC – 2021: Section 303.1.1 – 303.1.4 – Situations with Assembly use that is not considered an Assembly Occupancy

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TRANSCRIPT

What is an Assembly Occupancy? 

DEFINITION

An assembly occupancy, also known as a Group A occupancy, is an occupancy involving “the use of a building or structure, or a portion thereof, for the gathering of persons for purposes such as civic, social or religious functions; recreation, food or drink consumption or awaiting transportation” as written in IBC Section 303.1. 

More simply stated, an assembly occupancy involves a space used for the gathering of people. The purposes described in the IBC definition are common for assembly occupancies, but they are not all-encompassing. There can certainly be other reasons for people to gather in an assembly occupancy. 

ASSEMBLY A-1

The IBC divides assembly occupancies into five groups, A-1 through A-5. For each of these, the code provides a description of the group and then a list of couple of examples. These examples are helpful in determining which group an assembly occupancy falls under, but they’re not an exhaustive list. 

First is Group A-1, which includes “assembly uses, usually with fixed seating, intended for the production and viewing of the performing arts or motion pictures.” Examples include motion picture theaters, symphony and concert halls, television and radio studios admitting an audience, and theaters.

ASSEMBLY A-2

Next is Group A-2, which includes “assembly uses intended for food and/or drink consumption.” Examples include 

Banquet halls, Casinos (gaming areas), Nightclubs, Restaurants, cafeterias and similar dining facilities (including their associated commercial kitchens), Taverns and bars. 

ASSEMBLY A-4

We’ll skip Group A-3 for a moment and jump to Group A-4, which includes “assembly uses intended for viewing of indoor sporting events and activities with spectator seating including.” Examples include Arenas, Skating rinks, Swimming pools, and Tennis courts. 

ASSEMBLY A-5

Group A-5 includes “assembly uses intended for participation in or viewing outdoor activities.” Examples include Amusement Park structures, Bleachers, Grandstands, and Stadiums. 

ASSEMBLY A-3

And finally, back to Group A-3, which includes “assembly uses intended for worship, recreation or amusement and other assembly uses not classified elsewhere in Group A.” Examples include: Amusement arcades, Art galleries, Bowling alleys, Community halls, Courtrooms, Dance halls (not including food or drink consumption), Exhibition halls, Funeral parlors, Greenhouses for the conservation and exhibition of plants that provide public access, Gymnasiums (without spectator seating), Indoor swimming pools (without spectator seating), Indoor tennis courts (without spectator seating), Lecture halls, Libraries, Museums, Places of religious worship, Pool and billiard parlors, and Waiting areas in transportation terminals.

ASSEMBLY REQUIREMENTS

Assembly occupancies have a variety of specific requirements in the IBC, such as special requirements for theaters in Chapter 4, requirements for voice fire alarm systems in chapter 9, and a whole subsection of means of egress requirements in Chapter 1030.  

In all of the code consulting that I’m involved in, one of the most common mistakes that I see is how designers treat small spaces used for assembly purposes.  

OFTEN MISSED ITEMS WITH ASSEMBLY OCCUPANCIES

IBC Chapter 3 gives four situations where a space used for assembly purposes is actually not classified as an assembly occupancy. 

First is small buildings and tenant spaces in IBC Section 303.1.1, which states that “A building or tenant space used for assembly purposes with an occupant load of less than 50 persons shall be classified as a Group B occupancy.” 

So, if your entire building has an occupant load of less than 50 or if your tenant space has an occupant load of less than 50, even though it is used for assembly purposes, it is not an Assembly Group A occupancy. Rather, it is a Group B occupancy.

IBC Section 303.1.2 states a similar concept, that any room or space that is used for assembly purposes and is accessory to another occupancy shall be classified as either a Group B occupancy or as part of the other occupancy, when the occupant load of the space is less than 50 or the area of the room is less than 750 SF. 

These two situations should be fairly easy to understand, but architects and engineers get this wrong all the time.  

Generally, if your assembly-use space is less than 750 square feet or if it contains less than 50 occupants, it’s likely not an assembly occupancy. 

One important concept to keep in mind is that the occupant load factor used for a space is based on the function of the space, not the occupancy classification. 

So, a 500 sqft conference room located within a Business occupancy would not be considered an assembly occupancy, but you would still apply the occupant load factor of 1 person per 15 net square feet from IBC Table 1004.5 for Assembly: Tables and Chairs functions. 

Back to our small assembly situations, IBC 303.1.3 states that “A room or space used for assembly purposes that is associated with a Group E occupancy is not considered a separate occupancy.” So, a conference or meeting room in a high school building would not be considered an assembly occupancy, but just part of the Group E occupancy. 

And finally, IBC 303.1.4 states that “Accessory religious educational rooms and religious auditoriums with occupant loads of less than 100 per room or space are not considered separate occupancies.” This requirement works in the opposite manner as the previous three, in that a small space associated with a Group A-3 occupancy for religious worship is included within the Group A-3 occupancy. So, for example, a classroom or small auditorium that is part of a place of religious worship would not be classified as a separate Group E or Group B occupancy, but part of the main Group A-3 occupancy. 

These four situations are frequently overlooked or misunderstood, so I would suggest reviewing them anytime you work on a project that involves an assembly use space. 

SUMMARY

So, what is an assembly occupancy?  

In short, it is a building, structure or space used for the gathering of people. The IBC divides assembly occupancies into Groups A-1 through A-5 and provides a list of examples for each group. Remember that small spaces used for assembly purposes are often not classified as assembly occupancies.

I’m Chris Campbell, this is MeyerFire University.