IMC 607.5.5 through 607.5.7 covers shafts, rated exterior walls, and smoke partitions. Shaft penetrations are easy to oversimplify - sometimes dampers are required, sometimes they are prohibited, and sometimes the exception depends on upward airflow, steel subduct geometry, smoke control, or garage shaft separation.
Plain English: Plain-English Highlights
607.5.5 Shaft Enclosures
For a permitted duct or air-transfer opening through a shaft enclosure, the base rule calls for approved fire and smoke dampers installed per their listings. Evaluate fire-damper and smoke-damper exceptions separately; an exception to one does not waive the other. Where both remain, use a listed combination FD/SD or separate listed FD and SD devices.
607.5.5 Shaft Exceptions
FD steel-subduct exception: wall thickness ≥0.0187 in.; vertical rise ≥22 in. in the exhaust shaft; exhaust fan at the shaft upper terminus, powered continuously under IBC 909.11 to maintain continuous upward airflow outdoors. This FD exception does not waive an SD.
Other FD routes: an ASTM E119 or UL 263 penetration test as part of the rated assembly; approved IBC 909 smoke control where FD interferes; or garage exhaust/supply shafts separated from other building shafts by ≥2-hour fire-resistance-rated construction.
Named SD exhaust route: Group B or R occupancy equipped throughout with automatic sprinklers under IBC 903.3.1.1; kitchen, clothes-dryer, bathroom or toilet-room exhaust opening; steel wall ≥0.0187 in. and rise ≥22 in.; upper-terminus exhaust fan powered continuously under IBC 909.11, maintaining upward flow outdoors.
Other SD routes: garage exhaust/supply shaft separated from other building shafts by ≥2-hour rated construction, or approved IBC 909 mechanical smoke control where SD interferes. Neither automatically waives the FD.
Where the applicable kitchen or dryer exhaust provision prohibits a damper, §607.5.5 does not require an FD or combination FD/SD. Show the governing prohibition and separate shaft protection path.
607.5.5.1 Continuous Upward Flow
FD or SD cannot be installed where closure would stop required continuous upward airflow. When continuous upward flow is required, alternative shaft protection must be used.
607.5.5.2 Enclosure at the Bottom
Shafts that do not extend to the bottom of the building must be protected per IBC 713.11.
607.5.6 Exterior Walls
Ducts and air transfer openings in rated exterior walls requiring protected openings under IBC 705.12 need listed fire dampers.
607.5.7 Smoke Partitions
Section 607.5.7 specifically requires listed smoke dampers at air-transfer openings through smoke partitions. The mere passage of a duct is not the stated trigger.
Exception: where a SD would interfere with required smoke control, approved alternative protection is required. The exception does not allow unprotected openings.
On Plans: Why it matters
Shaft penetrations are easy to oversimplify. Sometimes dampers are required. Sometimes they are prohibited. Sometimes the exception depends on upward airflow, steel subduct geometry, smoke control, or garage shaft separation. A fire damper in a grease exhaust shaft is not a conservative choice - it is a prohibited condition that increases fire risk.
Code Path: Where to show it - M-001: IMC 607.5.5-607.5.7 notes and exception basis - M-101: openings at shafts, exterior walls, and smoke partitions with shaft type labeled - M-501: shaft penetration, subduct height, damper, sleeve, and access details - M-603: smoke control sequence and continuous exhaust fan operation basis - A / LS sheets: shaft ratings, exterior wall ratings, smoke partitions, and garage separation
Check: Show each claimed FD and SD route separately. For a steel-subduct claim, dimension ≥0.0187-in. wall and ≥22-in. rise; locate the upper-terminus fan and IBC 909.11 continuous power/airflow. For the named SD route, document Group B/R and IBC 903.3.1.1 sprinklers throughout. Document ≥2-hour garage-shaft separation where used.
Review Risk: Don't - Don't place dampers where code prohibits them - kitchen grease and dryer exhaust systems are prohibited-damper conditions - Don't omit shaft dampers without showing the exception basis - Don't ignore continuous fan operation when relying on the upward airflow exception
Field Tip: Field tip For shaft penetrations, ask: is this a supply shaft, exhaust shaft, smoke control shaft, garage shaft, or prohibited-damper system? That answer drives the damper, exception, or alternate protection. If you can't answer the shaft type from the drawings, the damper selection can't be verified.
MasterBuild QA Lens
The prohibited-damper condition is the most dangerous coordination error in 607.5.5. A fire damper in a grease exhaust shaft creates a grease accumulation point that increases fire risk. Confirm the shaft system type before specifying any damper. If the system is kitchen exhaust, the question is not 'which damper type' but 'this system cannot have a damper - what is the required alternative?'
Drawing / Submittal Check
For each shaft opening, label shaft type/rating and the distinct FD and SD outcomes. Record steel wall ≥0.0187 in., rise ≥22 in., upper-terminus fan, IBC 909.11 continuous power and outdoor upflow when a subduct path is claimed. The named SD route additionally needs Group B/R, IBC 903.3.1.1 sprinklers throughout and qualifying exhaust use. Show ≥2-hour separation for a garage route, damper prohibitions, and bottom protection under IBC 713.11 for partial-height shafts.
Common Review Risk
Three patterns: (1) subduct exception applied without showing subduct height, steel gauge, and fan operation; (2) fire damper shown in a grease exhaust or dryer exhaust shaft - both prohibited; (3) partial-height shaft without bottom protection. Each is a first-cycle comment.
When To Escalate
Escalate when a shaft serves multiple exhaust system types (requiring shaft separation coordination), when smoke control requires shafts to remain open during operation, or when the IBC 406.5 parking garage exception involves a configuration requiring PE verification.
Rated Assembly Coordination
Shaft enclosures are fire-resistance-rated assemblies. The shaft rating, duct material, damper or alternative protection, access, and smoke control coordination are a single compliance package. Missing any element is a plan review flag. Run the shaft penetration checklist as a coordinated review across M-101, M-501, M-603, and the architectural life-safety plan.
Model-code source: 2024 IMC chapter text. Verify the locally adopted edition, amendments, assembly, listing, and approved exception for a project.