IMC 607.5.5 through 607.5.7 cover shafts, rated exterior walls, and smoke partitions. Shaft penetrations are the section where damper requirements become most nuanced — sometimes a damper is required, sometimes it is specifically prohibited, and sometimes the code provides a subduct exception that requires documented upward airflow.
607.5.5 Shaft Enclosures: Ducts and air transfer openings that penetrate a shaft enclosure shall be protected with a listed fire damper. The damper must be installed per its listing at the shaft wall.
607.5.5.1 Subduct Exception: A fire damper is not required where a steel subduct at least 22 gage thick is used. The subduct must extend at least 22 inches (559 mm) vertically into the shaft, be continuously joined and sealed, and the system must be designed so that airflow is always upward (into the shaft) at that point.
607.5.5.2 Openings Other Than Duct Openings: Air transfer openings in a shaft enclosure other than duct openings shall be protected with a listed fire damper.
Damper Prohibited — Grease Duct Shafts and Laundry/Dryer Shafts: A fire damper SHALL NOT be installed in a grease duct or laundry/dryer exhaust duct shaft penetration. Installing a fire damper in a grease duct is a fire hazard — accumulated grease on the damper creates an ignition point. The code prohibits it explicitly.
607.5.6 Exterior Walls: Where ducts penetrate rated exterior walls, fire dampers are required per the assembly rating and opening protection requirements of IBC Chapter 7. The IMC defers to IBC 714 and IBC 717 for exterior wall penetration requirements.
607.5.7 Smoke Partitions: Ducts and air transfer openings penetrating a smoke partition shall be protected with a listed smoke damper. The SD must be actuated by a smoke detector installed in the duct or in the occupied space served by the duct, or by the fire alarm system.
Critical Rule: Fire dampers are PROHIBITED in grease exhaust ducts and laundry/dryer exhaust ducts serving shaft enclosures. A fire damper in a grease duct accumulates grease on the blade and creates an ignition point inside the duct. This is not a gray area — it is an explicit prohibition.
Why it matters: The shaft penetration is where the most coordination failures in Chapter 6 originate. The duct enters a shaft; the mechanical plan shows a fire damper symbol; the reviewer asks: ‘Is this a grease shaft? Is airflow upward? Is the subduct exception documented?’ Without answers, the drawing gets a correction. Getting the shaft coordination right requires knowing the shaft type, the duct system type, and the airflow direction before the damper schedule is finalized.
Where to show it: M-001 — shaft damper basis, subduct exception conditions if claimed. M-101 — FD at shaft walls, no FD at grease/laundry shafts, SD at smoke partitions. M-501 — FD details with sleeve, subduct detail showing 22-gage and 22-inch minimum dimensions if exception used. M-603 — SD activation sequence at smoke partitions.
Do: Identify every shaft type in the project before finalizing the damper schedule. Confirm whether airflow is upward before claiming the subduct exception. Show the subduct dimensions on M-501 if the exception is used. Show SD (not FD) at smoke partitions.
Don’t: Don’t install or specify a fire damper in a grease exhaust duct. Don’t claim the subduct exception without documenting airflow direction and subduct dimensions. Don’t show a fire damper at a smoke partition — that wall requires a smoke damper.
Field Tip: For each shaft on the project: (1) What system uses this shaft? (2) Is a fire damper required, prohibited, or is the subduct exception applicable? (3) Is airflow direction documented? If the shaft serves a grease exhaust or dryer exhaust, the fire damper symbol must not be there regardless of what the drawing convention shows.
Masterbuild QA Lens
IMC 607 damper requirements are triggered by the rated assembly type, not by the duct system. Confirm the assembly label from the architectural drawings before the damper schedule is finalized.
Drawing / Submittal Check
For every duct and transfer opening at a rated assembly: assembly type on M plan, damper type with listing, access location, sleeve and retaining angle details, exception basis on M-001 if applicable.
Common Review Risk
Damper type selected without identifying the assembly type. Exception applied without documenting all conditions. Access panel missing or not coordinated with ceiling or shaft construction.
When To Escalate
Escalate when the rated assembly type cannot be confirmed from architectural drawings, when smoke control and damper requirements conflict, or when the exception conditions cannot be established from the project documents.
Rated Assembly Coordination
The mechanical plan must match the architectural life-safety plan. Assembly labels, damper types, and exception bases must agree between the M drawings and the A/LS drawings. Disagreements discovered at permit review become correction comments.