/ Field knowledge · IMC 602
If it is a plenum, say so — and list what is in it.
IMC 602: a space used as a plenum that is not documented as one is the comment. Materials above the ceiling have to be listed for plenum use. Closing the ceiling before inspection is demolition later.
Educational 2024 IMC 602. Confirm adopted edition, fire areas, and flood elevation. This is not a plenum listing or a materials approval. Packet: 602 PDF · ES.
- Applies to supply, return, exhaust, relief, and ventilation air plenums. Limited to specific locations, limited to one fire area. Fuel-fired appliances are not allowed in a plenum.
- Enclosure materials exposed to airflow: IBC 703.3 or strict flame-spread/smoke-developed limits. Gypsum plenums only under limited temperature/dew-point conditions. Framing cavities have tight limits.
- Materials in plenums must be noncombustible unless they meet a specific allowance. Ducts, coverings, detectors, wiring, sprinklers, tubing, foam, plastic piping — each has its own listing path (UL 2043, NFPA 262, UL 2024, UL 1887, UL 1820, ASTM E84, UL 723 as applicable).
- Flood hazard: above IBC 1612 elevation, or designed to prevent water entry/accumulation and resist hydrostatic, hydrodynamic, and buoyancy effects.
TI junk above the ceiling
A plenum that was compliant at original construction and then accumulated non-rated cable during tenant improvements needs an audit before new above-ceiling work. List each plenum, function, and listing basis on M-001.
Source: DCT 602 · construction: 602.2 · materials/flood: 602.3–602.4 · ducts: Chapter 6 · dampers: 607.
What to send
Whether the ceiling is a return plenum, the fire-area map, and a photo of what’s already above the ceiling on a TI.
If the ceiling is the return
Send the RCP and whether this is a TI. MasterBuild will say whether 602 even applies — or the ceiling is already full of non-plenum cable.
Send Project Background+1 (786) 398-6940 · osmany.portal@masterbuildconsulting.com
MasterBuild provides engineering services under a written scope. Nothing on this page is project-specific engineering advice, a code interpretation for your project, or a representation about permit approval.