/ Field knowledge · IMC 607.5.5
A fire damper in a grease shaft is not “to be safe.”
Shaft penetrations are easy to oversimplify. Sometimes dampers are required. Sometimes they are prohibited. A fire damper in a grease-exhaust shaft is not a conservative choice — it is a prohibited condition that creates a grease accumulation point. Label the shaft type before picking a device.
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.
- Ducts and transfer openings through shaft enclosures generally require listed fire and smoke damper(s) installed per their listing.
- Subduct exception: fire dampers may be omitted for certain steel exhaust subducts that extend at least 22 inches vertically and a continuously powered fan maintains upward exhaust. Both at once. Show height, steel, fan operation, and airflow direction.
- Fire dampers may also be omitted where the penetration is tested as part of the rated assembly, where smoke control would be impaired, or at certain separated garage shafts. In certain Group B and R sprinklered buildings, smoke dampers may be omitted for kitchen, dryer, bathroom, and toilet exhaust openings using compliant steel subducts with continuous upward exhaust.
- Fire dampers and combination fire/smoke dampers are not required — and are specifically prohibited — in kitchen and dryer exhaust systems where dampers are prohibited by code. 607.5.5.1: do not install FD/SD where closure would stop required continuous upward airflow.
- 607.5.5.2: shafts that do not extend to the bottom of the building are protected per IBC 713.11. 607.5.6: rated exterior walls needing protected openings under IBC 705.12 need listed fire dampers. 607.5.7: air transfer openings through smoke partitions need listed smoke dampers (unless an SD would interfere with required smoke control — then approved alternative protection, not an unprotected 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: 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 plan, what the shaft carries (supply, toilet, grease, dryer, garage), and whether any damper is shown at those openings.
If someone put a fire damper in the grease or dryer shaft
Send the shaft type and the damper schedule. Masterbuild will say whether 607.5.5 still has a prohibited damper — or the 22-inch subduct exception still has no fan-operation basis.
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.