IMC 602.3.7-602.4 addresses materials and flood risks in plenums. Exposed materials must meet strict flame/spread and smoke limits, and plenums in flood zones must prevent water intrusion or resist hydrostatic forces.
Plain English: Plain-English Highlights
602.3.7 Foam Plastic
Foam plastic used as interior finish/trim must meet ASTM E84/UL 723 flame spread ≤25 and smoke ≤50, or be tested per NFPA 286 / IBC 2603.9.
Exceptions allow higher flame/smoke values if separated from airflow by a thermal barrier, corrosion-resistant steel, or 1-inch masonry/concrete.
602.3.8 Plastic Plumbing Piping and Tubing
Must be listed and labeled with flame spread ≤25 and smoke ≤50 (ASTM E84/UL 723).
Exception: UL 2846-listed water piping with defined smoke/flame performance.
602.3.9 Pipe and Duct Insulation
Insulation, adhesives, and coatings must meet flame spread ≤25, smoke ≤50 (ASTM E84/UL 723), and cannot flame, glow, smolder, or smoke per - ASTM C411 at service temperature ≥250°F.
602.3.10 Other Combustible Materials
Must be listed and labeled with flame spread ≤25 and smoke ≤50.
602.3.6 Discrete Electrical, Plumbing, Mechanical Products
Exposed products must be listed for plenum use per UL 2043.
Exception: metallic electrical enclosures.
602.4 Flood Hazard
Plenums in flood zones must be above IBC 1612 utility elevation or resist water entry, hydrostatic and buoyancy loads.
On Plans: Why it matters
Exposed foam, piping, insulation, and devices without proper listing or separation are common redlines. Flood-zone plenums are often overlooked in plan review.
Code Path: Where to show it
M-001: plenum-material and flood-hazard notes
M-101: plenum extents and exposed components
M-501: protection details for foam, insulation, piping, and enclosures
E / FP / P / controls sheets: listing basis and exceptions
Arch / civil: flood elevations and resistant construction
Check: Do
Call out the listing/test basis for all exposed materials
Show protection or separation where using exceptions
Coordinate flood-zone elevation with plenum location
Review Risk: Don't
Don't assume "above ceiling" is compliant
Don't place non-listed materials in plenums
Don't ignore flood design requirements
Field Tip: Field tip
Review the plenum like a product matrix: foam, plastic piping, insulation, adhesives, and exposed devices. Confirm listing, protection, and flood compliance.
Comment "IMC602" for a paste-ready plenum checklist + M-001 notes.
Masterbuild QA Lens
Duct-system sections are coordination sections. The question is not only whether air moves, but whether materials, insulation, plenums, dampers, access, and penetrations are correct for the location.
Drawing / Submittal Check
Trace the air path across plans, risers, details, schedules, specifications, and reflected ceiling constraints. Confirm duct material, insulation, vapor control, fire/smoke dampers, access, and exposed conditions.
Common Review Risk
Small duct notes create large field cost when they miss rated assemblies, plenum limitations, weather exposure, internal liner restrictions, damper access, or condensation control.
When To Escalate
Escalate when ducts cross rated construction, run outdoors, serve healthcare spaces, use internal lining, connect to smoke control, or pass through congested existing-building conditions.
Rated Assembly Coordination
When rated construction is involved, the drawings should identify the assembly, damper type, access location, actuator/control basis, fire alarm interface if applicable, and who coordinates the opening.
Load Assumption Check
For load-driven decisions, make the assumptions visible: weather basis, orientation, envelope, occupancy, ventilation, equipment gains, and any existing-building limitations that affect capacity.