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:
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 degrees 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:
Review the plenum like a product matrix: foam, plastic piping, insulation, adhesives, and exposed devices. Confirm listing, protection, and flood compliance.
Masterbuild QA Lens
Flood-hazard plenum requirements (602.4) require that all mechanical equipment, wiring, and utilities in plenums within flood-hazard areas be elevated to or above the design flood elevation. Confirm the equipment elevation matches the civil drawings and that the note on M-001 references the DFE rather than a generic flood zone designation.
Drawing / Submittal Check
For 602.3.7-602.4 (plenum materials and flood hazard): if the project is in a flood hazard area, M-001 must note the flood hazard zone and confirm that the plenum design accounts for potential flooding. For projects outside flood zones, M-001 should state 'not in flood hazard area' to prevent the reviewer from asking. Confirm the plenum is not serving as a water drainage path.
Common Review Risk
Flood hazard zone projects require plenum design to account for potential flooding. The most common error is a plenum designed normally in a flood zone - the electrical, mechanical, and structural systems in the plenum must be flood-resistant above the design flood elevation. Confirm flood hazard zone applicability on M-001. A plenum that floods and shorts out electrical systems is a life-safety issue.
When To Escalate
Escalate when the project is in a flood hazard area and the plenum contains mechanical and electrical equipment that has not been flood-proofed. FEMA and the local floodplain administrator have jurisdiction over flood hazard area installations in addition to the building official. Confirm the review path with all authorities before the permit is filed.
Rated Assembly Coordination
Sections 602.3.7-602.4 address plenum material restrictions and separation from adjacent spaces. Where the plenum is adjacent to a rated shaft or corridor, confirm the common wall meets the rated assembly requirement and is not compromised by plenum openings.
Load Assumption Check
Plenum material restrictions in 602.3.7-602.4 may eliminate some insulation or duct liner products, requiring a higher R-value assembly with less thickness. Confirm the plenum-rated insulation system achieves the required R-value and that this is reflected in the energy model or load calculation.