Daily Code Talk — IMC 604 (Insulation): Mini-Series Kickoff

Duct insulation is not just an energy item. IMC 604 ties together energy compliance, surface temperature, fire/smoke performance, vapor control, weather protection, fire damper clearance, and service access.A duct can be sized and installed correctly, but still fail review if the insulation system is not listed, labeled, continuous, protected, and coordinated with fire-rated assemblies.We’ll cover IMC 604 in five parts:• Part 1 (604.1–604.5): General rules, temperature, coverings, linings, and foam plastic- IECC coordination, 120°F surface temperature limit, flame-spread/smoke-developed criteria, ASTM E84 / UL 723, ASTM C411, listed/labeled requirements, foam plastic, and internally insulated appliances.• Part 2 (604.6–604.7): Penetrations and insulation identification- Duct coverings cannot penetrate rated or fireblocked assemblies. External insulation and factory-insulated flex duct must show manufacturer, R-value, installed thickness basis, and flame/smoke indices at required intervals.• Part 3 (604.8–604.10): Lining installation, thermal continuity, and service openings- Liner interruptions at fire dampers and heaters, metal nosings/sleeves at exposed liner edges, equal thermal performance where liner is interrupted, and service openings that cannot be buried by insulation unless identified.• Part 4 (604.11–604.12): Vapor retarders and weatherproof barriers- Cooling ducts need vapor-retarder continuity, seams sealed, low-perm criteria, spray foam exception, and approved weatherproof protection for insulated exterior ducts.• Part 5 (604.13): Internal insulation exposed to airstream- Internal insulation must be durable per UL 181, and water-permeable exposed internal insulation cannot line ducts or plenums from the cooling coil discharge to the downstream end of the drain pan.🏗️ Why it mattersMost IMC 604 redlines are coordination redlines: insulation crossing rated assemblies, missing product identification, no vapor-retarder continuity, exterior duct wrap with no weather barrier, liner blocking fire damper operation, or internal insulation placed where condensate risk is highest.🗺️ Where to show it• M-001: IMC 604 insulation notes, IECC basis, vapor retarder, and listing requirements• M-101: duct insulation locations, exterior ducts, and cooled duct routing• M-501: rated-assembly penetration details, fire damper/liner details, vapor barrier and weatherproofing details• M-601: duct insulation schedule with R-value, installed thickness, vapor retarder, flame/smoke rating, and listing basis• A / LS coordination: rated walls/floors, fireblocking, damper locations, and access panelsComment “IMC604” if you want a paste-ready duct insulation review checklist + M-001 note set.