Domain 2: Occupancy Classification, Construction Type, and Building Limits
This domain tests your ability to classify a building or tenant space, identify its type of construction, and apply height, area, and fire-resistance limits - including sprinkler and frontage increases, and the upgrade triggers that follow a change of use.
Classifying the use
- The IFC use groups are A, B, E, F, H, I, M, R, S, and U. Classify by the activity, not by the tenant's sign, business license, or corporate name.
- Where several uses share a building, you can treat it as non-separated mixed occupancy (most restrictive group governs), separated mixed occupancy with rated fire barriers, or an accessory occupancy limited to 10 percent of the story's floor area and never Group H.
- Incidental uses - boiler rooms, laboratories, flammable-liquid storage rooms - are protected under the incidental-use provisions even though they do not create a separate occupancy.
Construction type and limits
- Types I through V with A and B subtypes; the 2021 IBC restructures Type IV into IV-A, IV-B, and IV-HT (heavy timber).
- One table establishes structural fire resistance, one sets allowable stories and height, and one sets allowable area per story.
- NFPA 13 sprinkler protection generally buys one additional story and 20 feet of height for most use groups, plus substantial area increases; frontage on public ways adds area as well.
- A change of use can force separation, sprinkler, or egress upgrades under the existing building code even when the structure is untouched.
Worked example
A 4,800-square-foot, single-story building contains 420 square feet of offices and 4,380 square feet of mercantile. Is a fire barrier required between them? Reasoning: 420 ÷ 4,800 = 8.75 percent, under the 10 percent accessory limit, and Group B is not a prohibited accessory use - so the office is an accessory occupancy and the building is classified Group M. Occupant load and egress are still computed with the office area counted as business use.
Traps that cost marks
Assuming a separation is always required for mixed uses; applying the sprinkler height and area increases when the system is not an NFPA 13 system; classifying by signage; forgetting that storage height and commodity can change the hazard even when the occupancy group does not.