IBC Interior Finishes

Summary

Interior finish rules rate wall and ceiling finishes Class A, B, or C by flame spread and smoke development, and floor finishes Class I or II by critical radiant flux, with stricter classes in exits and corridors than in rooms. They govern what can be specified for paneling, wall coverings, acoustic ceilings, and carpet, and the limits ease where the building is sprinklered.

Cols

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Cites the 2024 IBC, Chapter 8. Always verify the adopted code edition and local amendments for the project jurisdiction
Covers interior wall and ceiling finishes, floor finishes, and decorative materials. Rated assemblies and the structure behind the finish are in other notes
Finish classes apply to the exposed surface, not to the wall assembly rating
Exit stairways, exit passageways, corridors, and rooms or enclosed spaces are the three locations the table distinguishes

Terminology

Flame spread index: relative rate of flame travel on a surface in the ASTM E84 tunnel test
Smoke-developed index: relative smoke produced in the same test
Class A, B, C (walls and ceilings): flame spread index 0 to 25 (A), 26 to 75 (B), 76 to 200 (C), each with smoke-developed index of 450 or less
Class I, II (floors): critical radiant flux of at least 0.45 W/sq cm (Class I) and at least 0.22 W/sq cm (Class II)
ASTM E84 / UL 723: surface burning characteristics test for wall and ceiling finishes
NFPA 286: room corner test, an alternative that qualifies a finish as Class A
ASTM E648 / NFPA 253: radiant panel test for floor coverings
Exit enclosures and exit passageways: the enclosed exit components, the strictest location
Rooms and enclosed spaces: areas enclosed by full-height partitions; occupancy of the room governs
Decorative materials: curtains, drapes, and similar items in assembly and other occupancies
Trim: baseboards, window casings, and similar items, limited to Class C

Requirements

Wall and ceiling classes

IBC 2024, Section 803.1.2: classes are determined by ASTM E84 or UL 723

Class	Flame spread index	Smoke-developed index
A	0 to 25	450 or less
B	26 to 75	450 or less
C	76 to 200	450 or less

IBC 2024, Section 803.1.1: a finish that passes NFPA 286 is treated as Class A when it meets the room corner criteria: flames do not spread to the ceiling during the 40 kW exposure, do not reach the outer edge of the sample, flashover does not occur, peak heat release rate is 800 kW or less, and total smoke released is 1,000 sq m or less
IBC 2024, Section 803.1: a material tested under Section 803.1.1 need not also be tested under 803.1.2

Required class by occupancy

IBC 2024, Table 803.13: minimum wall and ceiling finish class; sprinklered means sprinklered throughout (Section 903.3.1.1 or 903.3.1.2)

Group	Exit stairs and passageways, sprinklered	Corridors, sprinklered	Rooms, sprinklered	Exit stairs and passageways, not sprinklered	Corridors, not sprinklered	Rooms, not sprinklered
A-1, A-2	B	B	C	A	A	B
A-3, A-4, A-5	B	B	C	A	A	C
B, E, M, R-1	B	C	C	A	B	C
F	C	C	C	B	C	C
R-2	C	C	C	B	B	C
R-3	C	C	C	C	C	C
S	C	C	C	B	B	C
U	No restrictions	No restrictions	No restrictions	No restrictions	No restrictions	No restrictions

IBC 2024, Table 803.13, footnotes: Class C is allowed in assembly rooms with an occupant load of 300 or less; lobbies in A-1, A-2, and A-3 are at least Class B; Class C wainscoting or paneling up to 1,000 sq ft is allowed in a grade lobby over a noncombustible base; Class B wainscoting up to 48 in. above the floor is allowed in corridors and exit access stairs of Group I-3
IBC 2024, Table 803.13: Groups H, I-2, I-3, I-4, and R-4 carry their own, stricter entries; groups I-1, R-2.1 and others are read from the full table

Floor finishes

IBC 2024, Section 804.1: floor finish requirements apply to carpet-type coverings; traditional finishes such as wood, vinyl, linoleum, and terrazzo, and nonfibrous resilient coverings, are excepted
IBC 2024, Section 804.2: Class I requires a critical radiant flux of at least 0.45 W/sq cm; Class II at least 0.22 W/sq cm, tested to ASTM E648 or NFPA 253
IBC 2024, Section 804.3: testing and identification, with hang tags; carpet is tested as proposed for use, with the underlayment
IBC 2024, Section 804.4.1: carpet-type coverings meet DOC FF-1 (16 CFR 1630) or ASTM D2859 in all occupancies
IBC 2024, Section 804.4.2: in exit stairways and ramps, exit passageways, corridors, and rooms not separated by full-height partitions, Class I is required in Groups I-1, I-2, and I-3, and Class II in Groups A, B, E, H, I-4, M, R-1, R-2, and S; sprinklered buildings may substitute Class II where Class I is required

Decorative materials and trim

IBC 2024, Section 806.2: decorative materials are limited to 10 percent of the aggregate wall area in the space
IBC 2024, Section 806.4: curtains, draperies, and similar items pass NFPA 701 or NFPA 289
IBC 2024, Section 806.6: trim is Class C at minimum

Worked examples

Office building, sprinklered

Group B, sprinklered throughout (Section 903.3.1.1).

Location	Wall and ceiling class	Carpet
Exit stair enclosure	Class B	Class II
Corridor	Class C	Class II
Open office and rooms	Class C	Class II where the area is open to the corridor; none in rooms separated by full-height partitions

The sprinkler substitution lowers Class I to Class II only, so Group B stays at Class II.

Restaurant, not sprinklered

Group A-2, not sprinklered.

Location	Wall and ceiling class
Exit stair enclosure	Class A
Corridor	Class A
Dining room	Class B (Class C if the occupant load is 300 or less)

Adding sprinklers lowers each requirement by one class in this table, which is a common trade for cost and finish choice.

Acoustic ceiling tile check

Step	Check	Result
Product data	Flame spread 25, smoke developed 100 (ASTM E84)	Class A
Corridor, Group B, sprinklered	Class C required	Passes
Exit stair, Group A-2, not sprinklered	Class A required	Passes

Coordination

Sprinkler status: sprinklers relax the table by one class in most rows; confirm the system covers the area before specifying
Spec writing: require the E84 or NFPA 286 report and the maximum indices in the finish sections
Wall coverings and paint: vinyl wall coverings, fabric-wrapped panels, and foam acoustic products often test as Class B or C; check each product
Carpet: tag each carpet with its critical radiant flux; the underlayment is part of the tested system
Exposed wood and mass timber: exposed structural wood and wood paneling are finishes in the table; mass timber has its own protection and exposure rules in the construction type provisions
Mock-ups and substitutions: submittals and field substitutions need the same class

Common issues

Class confusion: classes A, B, and C are lower-is-better for flame spread (A is best); Class I and II for floors are the opposite (higher radiant flux is better)
Rooms versus corridors: an open plan with no full-height partitions makes the whole area a corridor-type space for floor finish purposes
Foam and plastics: exposed foam plastic needs separate approvals (Chapter 26) beyond E84
Adhesive and substrate: a finish class is valid only for the tested assembly, including backing and adhesive
Decorative materials above 10 percent: felt, fabric, and acoustic panels on walls can pass the limit quickly
Textiles: curtains and drapes need NFPA 701 or NFPA 289, not E84

Standards

ASTM E84 / UL 723: surface burning characteristics of building materials, the basis of Class A, B, and C
NFPA 286: room corner fire test, the alternative path to Class A
ASTM E648 / NFPA 253: critical radiant flux of floor covering systems
DOC FF-1 (16 CFR 1630) and ASTM D2859: surface flammability of carpets and rugs
NFPA 701 and NFPA 289: fire tests for textiles and decorative materials

Sources

GoCodebook: 2025 California Building Code, Section 803 wall and ceiling finishes (based on the 2024 IBC), https://gocodebook.com/library/us/ca/ca-building-code/chapter-8-interior-finishes/section-803-wall-and-ceiling-finishes
UpCodes: 2024 IBC Chapter 8 interior finishes (Department of Defense adoption), https://up.codes/viewer/department-of-defense/ibc-2024/chapter/8/interior-finishes