/ Field knowledge · IMC 607.5.5
A fire damper in a grease shaft is not “to be safe.”
A permitted shaft opening starts with listed fire-damper (FD) and smoke-damper (SD) protection. Section 607.5.5 has separate, conditional exceptions for each. A 22-inch subduct alone is not an exception; steel thickness, upper-terminus fan, continuous IBC 909.11 power and upward outdoor flow matter. Kitchen and dryer damper prohibitions are independent.
Educational 2024 International Mechanical Code (IMC) 607.5.5–607.5.7 from Daily Code Talk. Confirm the adopted edition. Distinct from 607.5.4 corridors and dryer exhaust (504). This is not a shaft design. Packet: 607.5.5 PDF · ES.
- Base rule: permitted duct and air-transfer openings through shaft enclosures require listed FD and SD protection installed per listing. Evaluate an exception for each device separately; waiving an FD does not waive an SD.
- FD steel-subduct route, 607.5.5(1.1): exhaust subduct wall thickness ≥0.0187 in. steel; vertical extension ≥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. Verify every condition on the plans and fan/power sequence.
- Other FD routes: a penetration tested under ASTM E119 or UL 263 as part of the rated assembly; an approved IBC 909 smoke-control system where the FD interferes; or a parking-garage exhaust/supply shaft separated from other building shafts by ≥2-hour fire-resistance-rated construction.
- SD named-exhaust route, 607.5.5(2): Group B or R occupancy with automatic sprinklers throughout under IBC 903.3.1.1; kitchen, clothes-dryer, bathroom or toilet-room exhaust opening; steel subduct wall ≥0.0187 in. and rise ≥22 in.; upper-terminus fan continuously powered under IBC 909.11 with upward flow outdoors. A different sprinkler basis or unverified fan power does not establish this route.
- Other SD routes: parking-garage exhaust/supply shaft separated from other shafts by ≥2-hour rated construction, or approved IBC 909 mechanical smoke control where the SD interferes. Keep the FD decision separate.
- Damper prohibition: where this code prohibits dampers in kitchen or clothes-dryer exhaust, 607.5.5 does not require an FD or combination FD/SD. Under 607.5.5.1, no FD or SD may close off a shaft required to keep continuous upward airflow. Show the applicable alternative protection and still review other requirements.
- Partial-height shaft bottoms follow IBC 713.11. Smoke-partition air-transfer openings have a separate 607.5.7 SD trigger; do not treat every duct crossing as the same opening.
On the set: shaft type labeled on M-101 (supply, exhaust, smoke control, garage, or prohibited-damper system), subduct height, alternative protection for grease/dryer, bottom-of-shaft protection for partial-height shafts.
A fire damper in the grease shaft “to be safe”
Grease accumulation, increased fire risk. The question is not which damper type — it is what alternative protection this prohibited-damper system needs. Same pattern on dryer exhaust.
Source: 2024 IMC §§607.5.5–607.5.7 · Daily Code Talk — IMC 607.5.5–607.5.7 · tool: Shaft-type screen · grease: Type I · dryer: 504.
What to send
Life-safety/shaft plans, duct use and occupancy, sprinkler basis, exact FD and SD exception claimed, subduct steel and rise, upper-fan location/power/airflow evidence, garage separation, and the proposed damper schedule.
If the shaft damper decision is unresolved
Send the shaft plan, fan sequence and damper schedule. MasterBuild can scope the separate FD and SD paths and any prohibited-device issue.
Send Project Background+1 (786) 398-6940 · osmany.portal@masterbuildconsulting.com
MasterBuild provides engineering services under a written scope. Nothing on this page is project-specific engineering advice, a code interpretation for your project, or a representation about permit approval. Confirm the adopted edition. The 22-inch subduct, prohibited kitchen/dryer dampers, and IBC 713.11 bottom protection are 2024 IMC 607.5.5 education from Daily Code Talk — not a shaft or damper design. This page is not legal advice.