Daily Code Talk: IMC 602 Summary (

Plenums)🧠 Plain-English Highlights• 602.1 general rules- IMC 602 applies to supply, return, exhaust, relief, and ventilation air plenums.- Plenums are limited to specific locations, limited to one fire area, and fuel-fired appliances are not allowed within a plenum. • 602.2 construction of plenums- Plenum enclosure materials exposed to airflow must meet IBC 703.3 or strict flame-spread and smoke-developed limits.- Gypsum-board plenums are allowed only under limited temperature/dew-point conditions, and framing cavities have tight limits on use, fireblocking, rated assemblies, floor-to-floor continuity, and exterior wall use. • 602.3 materials within plenums- Materials in plenums must be noncombustible unless they meet a specific code allowance.- Ducts, coverings, smoke detectors, wiring, sprinkler piping, pneumatic tubing, and discrete products each have their own listing/labelling path.- UL 2043, NFPA 262, UL 2024, UL 1887, UL 1820, ASTM E84, and UL 723 all show up here for a reason. • 602.3.7–602.3.10 product-specific combustible materials- Foam plastic, plastic plumbing piping/tubing, pipe and duct insulation, and other combustible materials all require very specific test/listing criteria.- Some exception paths exist, but only where the protective layer, listing basis, or composite assembly basis is clearly shown. • 602.4 flood hazard- In flood hazard areas, plenums must either be above the required IBC 1612 elevation or be designed to prevent water entry/accumulation and resist hydrostatic, hydrodynamic, and buoyancy effects. 🏗️ Why it mattersMost IMC 602 failures are not “duct layout” failures. They are coordination failures: a space is used as a plenum but not documented as one, materials above the ceiling are not actually plenum-compliant, framing cavities are used too loosely, or flood-zone conditions were never carried into the mechanical design. 🗺️ Where to show it• M-001: plenum basis-of-design notes, restrictions, material criteria, and exception paths• M-101 / coordination plans: plenum extents, air path, and exposed MEP components• M-501 / details: gypsum plenums, framing-cavity plenums, fireblocking, penetrations, enclosure/protection details• Schedules / product notes: listing basis for wiring, tubing, piping, insulation, foam, and discrete devices• A / LS / E / FP / P / civil sheets: fire areas, rated assemblies, detector coordination, sprinkler/piping basis, and flood elevation coordination🔧 Field tipBefore issue, do one plenum-only QC pass across the set:location → fire area → exposed material → listing/protection basis → flood conditionIf any one of those five is unclear, expect a redline.Comment “IMC602” if you want a paste-ready plenum review checklist + M-001 note set.