Definitions?

[Yankee Chronicler]

The IBC discusses/regulates "occupancy classification" and "use" (Chapter 3), yet the code doesn't define either term. I'm old enough that I began my career as an architect under my state's amended version of the BOCA Basic Building Code. Back then, if I remember correctly, all we had was "use groups." Them, somewhere along the way, the code introduced "occupancy classification" as something related to but different from "use group."

I'm trying to write a layman's guide to understanding the difference, and I'm not having any success. Can someone help me explain the distinction between "occupancy classification" and "use group"?

Thank you.

 

[steveray]

The groups are the major categories and the classification is under it....A vs. A3?...Just me talking out loud again with no backup...

 

[walker.t]

I'm trying to write a layman's guide to understanding the difference, and I'm not having any success.

I think they’re synonymous, to avoid confusion references to “use group” should be replaced with “occupancy classification.”

Searching through the 2021 IBC Commentary (Volume 1) PDF I find four instances of “use group”:

1. 312.1.1: “Greenhouses not classified as another occupancy shall be classified as Use Group U.” This is 100% a typo in my opinion, adding “Use” is an error, the title of Section 312 is “Utility and Miscellaneous Group U,” not “Utility and Miscellaneous Use Group U.”
2. Commentary on 503.1.4 Occupied Roofs, third bullet point: “Occupancy is established in accordance with Section 302.1. It requires that the use of a roof be classified in the use group category it most nearly resembles. The code relies on occupancy classification…”. “Use group category” is a poor choice of words, we know from Table 1004.5 that a space may have a use (“function of space”) that may not match the name of the occupancy classification, such as a business use in an Assembly building, or an assembly use in a Business building.
3. Commentary Figure 507.8.1.1 “Use Group H-2 Not Located at the Perimeter of an Unlimited Area Building.” “Use Group” should be just “Group,” Section 307 is titled “High-Hazard Group H,” not “High-Hazard Use Group H.”
4. Commentary on 510.7 Open Parking Garage Beneath Groups A, I, B, M and R, Point 1: “The height (measured both in feet and stories) and area of the open parking structure comprising a part of a mixed-use group building…”. Chapter 508 is titled “Occupancy Classification and Use,” but considering the previous points that is an error, it should be just “Occupancy Classification.”

Maybe there are other instances to “use group” in Volume 2 that I’m missing?

My guess is any references to “use” (when related to occupancy classification, not use of a space for occupant load calculation) stem from people who know the code so well that when they read “use” their brain is interpreting it as “occupancy.”

 

[arwat23]

Isn't 302.1 basically the definition of "Occupancy Classification" and 302.2 basically the definition of "Use" or "Use Designation"? Honest question, because I've never really thought about this...

Occupancy classification is the primary purpose of the building, where the Use is the functional designation specified within the group. Think A-1 vs A-2; both are Assembly, but the use (theater vs restaurant) dictates the occupancy classification group and changes what's required for the space.

 

[mtlogcabin]

Occupancy Classification applies to the whole building

Occupancy use is the individual spaces within the building and what those spaces are being used for.
Think of accessory uses within a "B" occupancy such as a conference room over 750 sq feet is an "A" use within a "B" occupancy building.
An S-1 building that will have offices "B" uses in that same building.

 

[Yikes]

In my initial take, Occupancy Classification is what the codes calls "Group", and the function more detailed within that Group is called "Use"

In the example below, "Assembly A-3" is the Occupancy group classification.
The "Uses" are the list of things that fit within that classification: Amusement arcades, art galleries, bowling alleys, community halls, etc.

303.4 Assembly Group A-3​

Group A-3 occupancy includes assembly uses intended for worship, recreation or amusement and other assembly uses not classified elsewhere in Group A including, but not limited to:

• Amusement arcades
• Art galleries
• Bowling alleys
• Community halls
• Courtrooms
• ...