IBC Occupancy Classification Guide: Groups A to U
Helonic is an AI construction drawing analysis platform for teams reading IBC occupancy classification guidance during drawing review.
A reference for architects, code consultants, and GC preconstruction teams checking occupancy assumptions on a drawing set.
IBC occupancy classification places every building or space in one of 10 groups defined in Chapter 3: Assembly (A), Business (B), Educational (E), Factory (F), High Hazard (H), Institutional (I), Mercantile (M), Residential (R), Storage (S), and Utility (U). Most groups split into subgroups, such as A-1 to A-5 or R-1 to R-4, based on use and hazard.
The group you pick sets allowable height and area, the required construction type, egress design, sprinkler triggers, and plumbing fixture counts. A wrong classification found at permit review can force changes to fire protection, egress, and rated separations across the whole set, so it pays to check it before the drawings go out.
What are the 10 IBC occupancy groups?
The IBC defines 10 occupancy groups in Sections 303 through 312. Several groups are divided further by hazard level or the kind of care provided, which gives 26 classifications in total. The table below lists each one with typical examples and the threshold that usually decides it.
| Group | Name | Examples | Threshold |
|---|---|---|---|
| A-1 | Assembly, fixed seating | Theaters, concert halls, TV studios with an audience | 50 or more occupants |
| A-2 | Assembly, food and drink | Restaurants, bars, nightclubs, banquet halls | 50 or more occupants |
| A-3 | Assembly, worship and recreation | Churches, libraries, museums, gyms without spectator seating, courtrooms | 50 or more occupants |
| A-4 | Assembly, indoor sports with spectators | Arenas, skating rinks, swimming pools, tennis courts | 50 or more occupants |
| A-5 | Assembly, outdoor | Stadiums, grandstands, bleachers, amusement park structures | 50 or more occupants |
| B | Business | Offices, banks, outpatient clinics, education above 12th grade | Any |
| E | Educational | K-12 schools, day care for more than 5 children older than 2.5 years | Any |
| F-1 | Factory, moderate hazard | Appliance manufacturing, furniture, printing, food processing | Any |
| F-2 | Factory, low hazard | Brick, glass, ice, metal products, beverages up to 16% alcohol | Any |
| H-1 | High hazard, detonation | Explosives manufacturing and storage | Above maximum allowable quantities (Table 307.1) |
| H-2 | High hazard, deflagration | Flammable gases, Class I flammable liquids, combustible dusts | Above maximum allowable quantities (Table 307.1) |
| H-3 | High hazard, physical | Combustible fibers, oxidizers, organic peroxides | Above maximum allowable quantities (Table 307.1) |
| H-4 | High hazard, health | Corrosives, toxic and highly toxic materials | Above maximum allowable quantities (Table 307.1) |
| H-5 | High hazard, HPM | Semiconductor fabrication facilities | Any |
| I-1 | Institutional, supervised | Assisted living, halfway houses, group homes | More than 16 persons |
| I-2 | Institutional, medical | Hospitals, nursing homes, psychiatric hospitals | Any |
| I-3 | Institutional, restrained | Prisons, jails, detention centers | More than 5 persons |
| I-4 | Institutional, day care | Adult day care, child day care for children 2.5 years or younger | More than 5 persons |
| M | Mercantile | Retail stores, markets, showrooms, motor fuel dispensing | Any |
| R-1 | Residential, transient | Hotels, motels, transient boarding houses | Any |
| R-2 | Residential, permanent | Apartments, condos, dormitories, monasteries | More than 2 dwelling units |
| R-3 | Residential, small | One- and two-family dwellings, care for 5 or fewer | 2 or fewer dwelling units |
| R-4 | Residential, care | Assisted living and residential care facilities | 6 to 16 persons |
| S-1 | Storage, moderate hazard | Furniture, lumber, tires, paper products, aircraft hangars | Any |
| S-2 | Storage, low hazard | Metal products, glass, parking garages | Any |
| U | Utility and miscellaneous | Barns, carports, greenhouses, sheds, tanks, towers | Any |
Why does occupancy classification matter?
Occupancy is the first input to almost every other code check. Change the group and the allowable building size, construction type, exits, and sprinklers can all change with it.
When you review a code analysis sheet, trace each of these back to the occupancy it assumes. If any of them uses a different group than the life safety plan, one of the two is wrong.
| What it controls | Where to check in the IBC |
|---|---|
| Allowable height, stories, and area | Tables 504.3, 504.4, and 506.2 |
| Required construction type | Chapter 6 and Table 601 |
| Occupant load and egress | Table 1004.5 and Chapter 10 |
| Automatic sprinkler requirements | Section 903.2 |
| Plumbing fixture counts | Table 2902.1 |
How do you classify a mixed-use building?
When a building holds more than one occupancy, IBC Section 508 gives three options. Most commercial projects use separated occupancies because each area can then follow its own rules.
| Option | IBC section | How it works |
|---|---|---|
| Accessory occupancies | 508.2 | A secondary use that takes up no more than 10% of the floor area of the story, and stays within the Table 506.2 nonsprinklered area for its own group, can be treated as part of the main occupancy without a rated separation. |
| Non-separated occupancies | 508.3 | No separation walls between uses. The whole building has to meet the most restrictive requirements of every occupancy present. |
| Separated occupancies | 508.4 | Fire barriers or horizontal assemblies separate each occupancy at the rating in Table 508.4. Each area follows its own requirements. |
What separation does IBC Table 508.4 require?
Table 508.4 lists the fire-resistance rating, in hours, between each pair of occupancies. The sprinklered column applies only when the building is sprinklered throughout under NFPA 13. "N" means no separation is required, and "NP" means the combination is not permitted.
The rows below are a sample. Check the full matrix in the code edition your jurisdiction adopted, along with any local amendments, before you finalize a code plan.
| Occupancies being separated | Sprinklered | Not sprinklered |
|---|---|---|
| A or E from A or E | N | N |
| A or E from R | 1 hour | 2 hours |
| A or E from B, F-1, M, or S-1 | 1 hour | 2 hours |
| B, F-1, M, or S-1 from each other | N | 1 hour |
| I-2 from other occupancies | 2 hours | NP |
| H-1 from any other occupancy | NP | NP |
| H-2 from A or E | 3 hours | 4 hours |
Which occupancy classification mistakes show up most?
The most common mistake is giving a small assembly room its own A classification. Under IBC 303.1.2, an assembly space with fewer than 50 occupants that is accessory to another use is classified as Group B or as part of the main occupancy. A 30-person conference room in an office is B, not A-3.
Mixing up R-1 and R-2 is the next one. R-1 covers transient occupants, which the IBC defines as stays of 30 days or less, such as hotels. R-2 covers permanent residents in apartments and dorms, and the difference changes egress and fire protection.
The third is overlooked storage. A storage room inside another occupancy can push past the accessory limits and become S-1 or S-2, which then needs its own separation or a non-separated design.
How do you check occupancy classification on a drawing set?
Start with the code analysis, usually on a G-series or life safety sheet. Note the occupancy group, construction type, sprinkler basis, and mixed-use option the design team chose.
Then compare that against the floor plans. Room names should match the occupancy shown on the life safety plan, occupant loads should use the right Table 1004.5 load factor for each use, and every separation the code plan relies on should appear on the plans as a rated wall with a matching assembly tag.
Finally, check the plumbing fixture count and the exit widths against the occupant loads. Those two numbers are where a classification change usually shows up first in the drawings.
How Helonic helps with IBC occupancy and code compliance review
Helonic analyzes 2D PDF drawing sets across 10 issue categories: coordination, code compliance, missing information, structural, MEP, fire safety, accessibility, constructability, dimensions, and QA/QC. For IBC occupancy and code compliance review, that means the software reads across sheets, flags likely issues with low, medium, or high severity, and gives the exact sheet coordinates for review.
Teams using Procore or Autodesk Construction Cloud can pull drawings and push accepted issues as RFIs in one click. Results typically come back in 15 to 30 minutes after the PDFs are uploaded, with no BIM or 3D model required. To see it on your own set, book a demo at /book-demo.
FAQ
What are the IBC occupancy classifications?
The IBC has 10 occupancy groups: Assembly (A), Business (B), Educational (E), Factory (F), High Hazard (H), Institutional (I), Mercantile (M), Residential (R), Storage (S), and Utility (U). Most are split into subgroups, such as A-1 to A-5, F-1 and F-2, H-1 to H-5, I-1 to I-4, R-1 to R-4, and S-1 and S-2.
When does assembly occupancy apply?
Group A applies when a space is designed for 50 or more people gathering for entertainment, worship, dining, recreation, or waiting for transportation. Smaller assembly spaces are usually classified with the main occupancy. A 30-person conference room in an office is B, not A-3.
How do I classify a building with multiple uses?
Use one of the three IBC 508 options. Accessory occupancies (508.2) work when the secondary use is no more than 10% of the story's floor area. Separated occupancies (508.4) use fire-rated separations from Table 508.4. Non-separated occupancies (508.3) make the whole building meet the most restrictive requirements.
What is the difference between R-1 and R-2?
R-1 is transient residential, where occupants stay 30 days or less, such as hotels and motels. R-2 is permanent residential with more than two dwelling units, such as apartments, condos, and dormitories.
What occupancy group is a restaurant?
A restaurant with 50 or more occupants is Group A-2. A small restaurant or takeout space with fewer than 50 occupants is usually classified as Group B under IBC 303.1.1.
What is the difference between a fire wall and a fire barrier?
A fire wall (IBC Section 706) is structurally independent, so a collapse on one side does not bring down the other, and it carries a 2 to 4 hour rating. A fire barrier (IBC Section 707) is a rated assembly used for occupancy separations, exit enclosures, and shafts, and it is not structurally independent.
Key takeaways
- The IBC defines 10 occupancy groups, A through U, with 26 classifications in total.
- Occupancy sets allowable size, construction type, egress, sprinklers, and fixture counts.
- Mixed-use buildings follow one of three IBC 508 options: accessory, non-separated, or separated.
- Table 508.4 ratings depend on sprinkler status, so confirm the sprinkler basis first.
- Small assembly rooms, R-1 versus R-2, and accessory storage cause most classification errors.
- Always verify against the adopted code edition and local amendments with the AHJ.
Milind Sagaram
Co-founder & CEO, HelonicMilind is the co-founder and CEO of Helonic, where he leads product and go-to-market for AI-powered construction drawing analysis. He works closely with general contractors, project managers, estimators, and owners to understand how drawing quality drives project outcomes - and where AI can reduce RFIs, change orders, and rework. Milind has interviewed hundreds of construction professionals across project delivery roles, from preconstruction estimators at ENR top-400 contractors to facilities directors at institutional owners, and uses those conversations to shape both product direction and the way Helonic talks about the work.
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How this page was researched: Developed from Helonic's /knowledge-base/ibc-occupancy-classification and reviewed against Helonic's 2026 drawing-analysis categories, RFI workflow, and product capabilities.
Last reviewed by Milind Sagaram · September 2026