Daily Code Talk #104: IMC 604 Part 3 (604.8–604.10 Lining Installation, Thermal Continuity, and Service Openings)IMC 604.8 through 604.10 is about what happens when duct insulation and lining meet real equipment conditions. This is where fire dampers, heaters, interrupted liner, and buried access panels can turn a clean duct detail into a coordination problem.

🧠 Plain-English Highlights• 604.8 Lining Installation- Duct liner must be interrupted at the area of operation of a fire damper.Duct liner must also be interrupted at least 6 inches upstream and 6 inches downstream of electric-resistance and fuel-burning heaters in the duct system.- Where exposed duct liner edges face opposite the direction of airflow, they must be protected with metal nosings or sleeves.• 604.9 Thermal Continuity- If duct liner is interrupted, a duct covering with equal thermal performance must be installed.- In other words, removing liner at a fire damper or heater does not eliminate the thermal requirement. The thermal performance still has to be maintained another way.• 604.10 Service Openings- Service openings cannot be concealed by duct coverings unless the exact location is properly identified.- If insulation covers an access opening, the field still needs to know exactly where that opening is.🏗️ Why it mattersThese comments usually come from coordination gaps. The mechanical detail may show lined duct, the fire damper detail may show a damper, and the heater schedule may show required clear space, but nobody carries the insulation transition through clearly. The result is interrupted liner with no thermal replacement, raw liner edges, or access panels lost under insulation.🗺️ Where to show it• M-001: IMC 604.8–604.10 note for liner interruptions, equal thermal replacement, and access identification• M-101: lined duct routing near dampers, heaters, and service-access locations• M-501: damper details, heater-adjacent liner interruption details, metal nosing details, and insulation transitions• M-601: duct insulation / lining schedule with equal thermal performance basis✅ Do• Interrupt duct liner where fire dampers and duct heaters require it• Show the replacement insulation method where liner is removed• Protect exposed liner edges with metal nosings or sleeves where required• Identify service openings if duct covering passes over them⛔ Don’t• Don’t run liner through the operating area of a fire damper• Don’t leave interrupted liner with no equal thermal replacement• Don’t bury service openings under insulation with no identification🔧 Field tipA good QC check is this: every time liner stops, ask what replaces it thermally and what protects the exposed edge. If the detail does not answer both, the drawing is probably incomplete.Comment “IMC604” if you want a paste-ready duct insulation review checklist + M-001 note set.