/ Field knowledge · IMC 601
A corridor is not a duct.
IMC 601: a corridor is not a duct. Return from a kitchen, garage, or another dwelling unit is not a default. Most 601 failures are coordination, not duct sizing.
Educational 2024 IMC 601. Confirm adopted edition and IBC exit/corridor provisions. This is not a duct design. Chapter 5 or 7 governs where they are more specific. Exception: ducts discharging combustible material directly into a combustion chamber must comply with NFPA 82. Packet: 601 PDF · ES.
- 601.2: corridors cannot serve as supply, return, exhaust, relief, or ventilation air ducts except for limited code-listed conditions. Corridor ceiling plenums as return only where a listed fire/smoke condition is met.
- 601.3: exit-enclosure ventilation must be independent of other building ventilation systems. Equipment, routing, intake/discharge, and rated separation follow this section and the IBC.
- 601.4: positive-pressure exhaust ducts, chimneys, and vents cannot extend into or pass through ducts or plenums unless a specific exception is met — listing, sealing, joint location, or enclosure then matter.
- 601.5: 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.
Return grille in the corridor
If the air path uses the corridor, an exit stair, or another dwelling unit, stop. Name the exception — or move the return. Room-by-room supply vs return on M-601 is the reviewable proof.
Source: DCT 601 · tool: return screen · undercuts: 601.5 jump ducts · plenums: 602 · transfer: 501.4 · dampers: 607.
What to send
Reflected-ceiling plan, rated-corridor plan, and whether any return lives in a kitchen, garage, closet, or corridor.
If the corridor is doing the return
Send the RCP. MasterBuild will say whether 601 even allows that path — or the return is in a prohibited room.
Send Project Background+1 (786) 398-6940 · osmany.portal@masterbuildconsulting.com
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