How to Determine Building Occupancy?

MeyerFire University | LS003.02

By Chris Campbell, PE

RELATED VIDEOS

• ​LS101.05: Different Approaches to Mixed-Occupancy Buildings?

RESOURCES

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

CODE & STANDARD REFERENCES

• IBC – 2021: Chapter 3 - Occupancy Classification and Use
• IBC – 2021: Section 303.1 & 303.2 – Small Assembly spaces not considered Assembly Occupancy
• IBC – 2021: Section 311.1 – Accessory storage areas categorized under main occupancy

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TRANSCRIPT

How to Determine Building Occupancy?

INTRODUCTION

The International Building Code, or IBC, defines a building’s occupancy classification as “the formal designation of the primary purpose of the building, structure or portion thereof” (from IBC Section 302.1).  

IBC Chapter 3 requires that all buildings be classified into one or more occupancy classifications.  

So, if your building is designed to the IBC, at least one occupancy classification is required.

IMPORTANCE

Occupancy classification is one of the most important factors in achieving code compliance, as most building code requirements depend on the occupancies present in a building.  

Allowable height and area, construction type, requirements for fire resistance-rated construction, fire protection requirements and egress requirements – all of these vary based on occupancy classification.

CODE REFERENCE

IBC Section 302.1 provides 10 occupancies: Assembly, Business, Educational, Factory and Industrial, High-Hazard, Institutional, Mercantile, Residential, Storage, and Utility and Miscellaneous, plus sub-groups within these. 

Classification of occupancy is based on the intended purpose of a building or portion of a building.  

So, in order to determine the occupancy, you need to know how the space will be used and potential hazards or risks associated with the function of the space. 

In some cases, the name of the room makes this readily apparent (for example, “storage room” or “bedroom” clearly convey the purpose of the room). But in other situations, you may need to consult with the architect or building owner to determine the purpose of a space. 

It's important to understand that the occupancy classification of a space is related to, but distinct from the use of a space.

USE VS. OCCUPANCY

The use of a space is a description of how the space is intended to be used: restaurant, library, bank, laboratory, nursing home, these are all uses. There is likely an infinite number of potential uses for a building or space.  

Many of them are listed throughout obviously Chapter 3 beneath each items category, but these are not an exhaustive list.  

The use of a space is important in determining the accuracy, the IBC only offers the 10 occupancy categories plus subcategories listed in Chapter 3.

MATCHING USE TO OCCUPANCY DESIGNATIONS

After determining the intended purpose of a building or space, the next step is to match this purpose to one of the use designations found in IBC Chapter 3.  

If the intended use and purpose of the space matches with one of the listed use designations, then the occupancy classification is simply the section under which that use designation in fact. 

For example, if your building contains a print shop, you would search the use designations found in IBC Chapter 3.  

Since print shop is listed as a use under section 304 Business Group B. You know that that portion of your building or space is a Group B occupancy. In many cases, a building contains multiple occupancies.  

The code provides several approaches for mixed occupancy buildings which we will cover in a separate video 

CLOSEST RESEMBLANCE

According to IBC section 302.1, if the intended purposes of your building or space is not specifically listed in Chapter 3, you need to select that occupancy category that most closely resembles your space based on the fire safety and relative hazard.  

It is impossible to list all potential uses of the building, so you may need to select the closest option if your use is not specifically listed.

OVERLOOKED PROVISIONS IN THE IBC

Now, there are several provisions in IBC Chapter 3 which are often overlooked.  

First is small assembly occupancies. According to IBC sections 303.1.1 and 303.1.2, there are several conditions where a space used for assembly purposes is not considered an assembly occupancy. For example, if a building or tenant space is used for assembly purposes and has an occupant load of less than 50, it is considered a Group B occupancy.  

Similarly, a room or space used for assembly purposes that is accessory to another occupancy with an occupant load of less than 50 or an area less than 750 square feet can be considered a Group E occupancy or part of that other occupancy.  

Second is accessory storage spaces, according to IBC Section 311.1.1, a room or space used for storage purposes that is accessory to another occupancy shall be classified as part of that occupancy.  

So, a storage room in an office or in a restaurant should be considered part of the main occupancy, not a Group S occupancy.  

SUMMARY

So, in summary, how do you determine building occupancy?  

First, you determine the intended purpose for the building or portion of the building.  

Next, you compare that purpose to the use designations in IBC Chapter 3 and classify the occupancy based on one of the 10 different occupancy categories.  

Remember that the use of a building or space can be almost anything, but the occupancy classification is limited to those listed in IBC Chapter 3.

I’m Chris Campbell, this is MeyerFire University.