Plain English:
601.1 scope
Chapter 6 governs duct systems for heating, cooling, ventilation, and exhaust unless Chapters 5 or 7 are more specific.
Exception: ducts discharging combustible material directly into a combustion chamber must comply with NFPA 82.
601.2-601.2.1 corridors + corridor ceiling plenums
Corridors cannot serve as supply, return, exhaust, relief, or ventilation air ducts except for limited code-listed conditions.
Corridor ceiling spaces can be used as return plenums only where one of the listed fire/smoke conditions is met.
601.3 exits
Exit enclosure ventilation must be independent of other building ventilation systems.
Equipment, duct routing, intake/discharge, and rated separation must follow the permitted arrangements in this section and the IBC.
601.4 contamination prevention
Positive-pressure exhaust ducts, chimneys, and vents cannot extend into or pass through ducts or plenums unless a specific exception is met.
If an exception is used, listing, sealing, joint location, or enclosure details matter.
601.5 return air openings
Return openings must maintain combustion-appliance clearance and cannot pull from hazardous, insanitary, or other prohibited spaces unless a listed exception applies.
Return taken from a room cannot exceed the supply delivered to that room.
Return air cannot cross dwelling units.
Closet, kitchen, pool, and garage conditions are exception-based, not blanket permission.
On Plans: Why it matters
Most IMC 601 failures are coordination failures, not duct-sizing failures. Common misses are corridor returns without code basis, exit ventilation tied into general systems, plenum routing that creates contamination risk, and return grilles placed in prohibited rooms.
Code Path: Where to show it
M-001: IMC 601 notes and exception criteria
M-101: supply, return, transfer, corridor, and exit air paths
M-501: corridor plenums, rated interfaces, closet returns, and separation details
M-601: room-by-room supply vs return checks
M-603 / controls: shutdown logic and interlocks
A / LS / E / FP / P / FG: ratings, detectors, sprinkler inputs, vent routing, and coordination
Check: Duct System Summary
M-001 must list each duct system with: service (supply, return, or exhaust), pressure class, material, gauge, insulation type and thickness, and the SMACNA construction standard.
Confirm the duct schedule addresses all duct sizes in the system and references the pressure class from M-001.
Show all fire and smoke damper locations on the duct plan with access panel locations on the reflected ceiling plan.
Review Risk:
Duct system changes during construction without updated drawings are the most common closeout problem - as-built conditions that don't match the permit set prevent the commissioning agent from reconciling airflow measurements.
A duct construction note that says 'all ductwork per SMACNA' without specifying the pressure class is a consistent first-cycle comment.
Missing duct insulation type and R-value documentation for each system (supply in unconditioned space, exhaust) is a routine plan review flag.
Field Tip:
Before issue, trace every non-obvious air path across the set:
corridor -> plenum -> exit enclosure -> return grille -> vent/exhaust routing -> exception basis
If the path is not clearly allowed and clearly coordinated, expect a redline.
Masterbuild QA Lens
For the Section 601 summary: confirm duct scope is defined (supply, return, exhaust, OA), system isolation per 601.3 is noted at rated construction, and every specialty duct application (liner, flexible, fire-resistive) is called out on M-001. These are process checks, not engineering checks - they cost nothing to add and prevent the most common 601 comments.
Drawing / Submittal Check
The duct system summary on M-001 should list each duct system with its service (supply, return, exhaust), pressure class, material, gauge, insulation type and thickness, and the SMACNA standard. A one-line summary per system prevents scattered comments across multiple sheets asking the same questions.
Common Review Risk
Duct system changes made during construction without updating the drawings are the most common closeout problem. The as-built conditions do not match the permit set, the commissioning agent cannot reconcile the airflow measurements with the design, and the building owner has no accurate documentation of the system. Confirm the contract requires as-built drawings before final payment.
When To Escalate
Escalate when the duct system scope changes significantly during construction and the as-built conditions will not match the permit set. Duct system changes that affect fire damper locations, rated assembly penetrations, or equipment connections require permit amendments before the work is done - not after. An as-built duct system that differs from the permit set without an amendment is a code violation.
Special Condition-Battery Rooms
For battery rooms or charging areas, confirm the battery type, hazard basis, ventilation calculation, control sequence, alarm interface, exhaust path, and AHJ or fire-protection coordination are all traceable. The drawing set should not leave the safety logic implied.
Rated Assembly Coordination
Chapter 601 coordination requires confirming prohibited duct locations, damper requirements at rated penetrations, and contamination separation at intakes. These are the foundation checks that must be complete before any other duct system detail can be finalized.