Occupancy groups: the IBC Chapter 3 classifications

One-line orientation

Occupancy classification sorts each building use into one of ten IBC groups. That choice affects construction type, allowable height and area, egress, and fire separation.

Key points

• Determining use and occupancy is the critical first step. Get this wrong and every downstream limit (construction type, allowable area, height, exits) is computed against the wrong rules.
• The ten groups:
  • A — Assembly: gatherings — theaters, restaurants, worship, arenas (subdivided A-1…A-5).
  • B — Business: offices, professional/service transactions, clinics — and colleges/universities.
  • E — Educational: schools through 12th grade.
  • F — Factory and Industrial: manufacturing/processing (F-1 moderate vs F-2 low hazard).
  • H — High-Hazard: materials posing a physical or health hazard (H-1…H-5).
  • I — Institutional: occupants supervised or incapable of self-preservation, or restrained (I-1…I-4).
  • M — Mercantile: display and sale of merchandise — stores, markets, malls.
  • R — Residential: dwelling/sleeping — hotels, apartments, houses (R-1…R-4).
  • S — Storage: storage of goods (S-1 moderate vs S-2 low hazard).
  • U — Utility and Miscellaneous: auxiliary structures — barns, carports, sheds, towers.
• Many groups subdivide by risk: F, S, and H split by hazard/combustibility; I and R split by the occupants’ condition and how many people are housed.
• Mixed use is normal. Real buildings combine groups (hotel + restaurant + garage); each space is classified independently before mixed-use provisions are applied.

Confusions / comparison

Group	Covers	Common trap
A Assembly	Theaters, restaurants, worship, arenas	A-2 = food/drink; A-3 = catch-all
B Business	Offices, clinics, colleges/universities	A university is B, not E
E Educational	Schools through grade 12	Stops at 12th grade
F Factory	Manufacturing/processing	F-1 vs F-2 = combustibility
H High-Hazard	Hazardous materials	Separate from F/S
I Institutional	Care / incapable / restrained	I vs R = self-preservation + count
M Mercantile	Retail display and sale	Not the same as B (no goods sold)
R Residential	Hotels, apartments, houses	Small-count I can drop to R
S Storage	Storage of goods	S-1 vs S-2 = combustibility
U Utility	Barns, sheds, carports, towers	The miscellaneous catch-all

Related

→ Assembly (Group A) (this module): the A-1…A-5 split · Institutional vs residential (this module): the I-vs-R self-preservation line · B / E / M (this module) · F / S / H / U (this module) · Construction types (this module): what occupancy drives next.