IMC Section 607.6-607.6.3

Daily Code Talk #119: IMC 607 Part 9 (607.6–607.6.3)

IMC 607.6 governs duct penetrations through horizontal assemblies — floors, floor/ceiling assemblies, and rated ceiling membranes. The protection path must be explicit on the drawings: a shaft, a floor-line fire damper, a ceiling radiation damper, a tested assembly, or a qualifying exception. The decisive questions are penetration type (through vs. membrane vs. nonrated), the number of stories connected, and whether the system runs during a fire — which drives dynamic vs. static CRD selection.

IMC 607.6 covers duct penetrations through horizontal assemblies — floors, floor/ceiling assemblies, and rated roof/ceiling membranes. The protection path must be explicit on the drawings: a shaft, a fire damper at the floor line, a ceiling radiation damper, a tested assembly, or a qualifying exception. A horizontal duct opening is never ‘just a floor penetration’ — the assembly rating, the number of stories connected, the penetration type, and whether the system runs during a fire all change what protection is required.

🧠 Plain-English Highlights

• 607.6 Horizontal Assemblies

Air duct penetrations through floors, floor/ceiling assemblies, or roof/ceiling membranes must be protected by an IBC 713 shaft enclosure, or comply with 607.6.1 through 607.6.3. Identify which path applies before detailing the penetration.

• 607.6.1 Through Penetrations

A duct through a rated floor/ceiling assembly connecting not more than two stories may avoid a shaft if a listed fire damper is installed at the floor line, or the duct is protected as a through-penetration firestop system per IBC 714.5.

Exception: in occupancies other than Groups I-2 and I-3, certain small steel ducts may penetrate three floors or fewer without a fire damper at each floor — but only if every condition is met simultaneously.

The conditions are cumulative: duct routed within a wall cavity, minimum 26 gage steel, serving a single dwelling or sleeping unit only, continuous to the exterior, maximum 4 inch diameter, within the code’s area limits, and with the annular space protected. Miss one condition and the exception does not apply.

• 607.6.2 Membrane Penetrations

Ducts and air transfer openings through a rated ceiling membrane generally require a shaft enclosure or a listed ceiling radiation damper (CRD).

Exceptions are narrow: tested assemblies, certain protected exhaust or outdoor-air duct penetrations, or tested duct outlet penetration systems. The exception must match the actual tested condition — not a similar one.

• 607.6.2.1 Ceiling Radiation Dampers

CRDs must be tested in accordance with 607.3.1 and installed per the rated assembly details, the manufacturer’s instructions, and the listing. A CRD is only valid as part of the specific tested floor/ceiling or roof/ceiling assembly.

• 607.6.2.1.1–607.6.2.1.2 Dynamic vs. Static Systems

A CRD in a system designed to operate during a fire must be listed for dynamic systems — rated for airflow and pressure during the fire event.

A static CRD is only permitted where the system is not designed to operate during a fire, unless a listed control closes the system and satisfies the listing’s static condition. Specifying a static CRD in a system that runs during a fire is a listing violation.

• 607.6.3 Nonrated Floor Assemblies

Even nonrated floor penetrations need protection: a shaft enclosure, noncombustible annular-space protection, or fire dampers, depending on how many stories the duct connects and the construction type.

Exception: fire dampers are not required in ducts contained entirely within an individual dwelling unit.

🏗️ Why it matters

Horizontal penetrations often look like simple floor or ceiling openings, so they get detailed like a diffuser boot. They are not. Protection changes based on the assembly rating, the number of stories connected, the penetration type (through vs. membrane), whether a shaft is used, the damper type, and whether the fan runs during a fire. A ceiling radiation damper is not interchangeable with a fire damper, and a static CRD is not interchangeable with a dynamic one — substituting either is a first-cycle comment at best and a failed inspection at worst.

🗺️ Where to show it • M-001: IMC 607.6 protection-path notes, the 607.6.1 exception conditions, and dynamic vs. static CRD basis • M-101: every horizontal-assembly penetration, with the assembly rating and story count labeled • M-501: shaft, floor-line fire damper, CRD, annular-space firestop, and duct-outlet penetration details • M-603: fan control sequence — confirm whether the system operates during a fire (drives dynamic vs. static) • A / LS sheets: floor/ceiling and roof/ceiling assembly ratings and listed assembly numbers

✅ Do • Identify each opening as a through penetration, a membrane penetration, or a nonrated floor penetration before selecting protection • Show the protection basis on the drawing: shaft, floor-line FD, CRD, or tested assembly number • For the 607.6.1 small-duct exception, show every condition (26 ga steel, ≤4 in dia, single unit, continuous to exterior, annular protection, story/area limits) • Match the CRD listing to the system’s fire-operation mode (dynamic vs. static)

⛔ Don’t • Don’t treat a rated ceiling-membrane penetration like a standard diffuser opening • Don’t specify a static CRD in a system intended to run during a fire • Don’t apply the 607.6.1 small-steel-duct exception without showing all of its conditions on the drawings • Don’t assume a nonrated floor needs no protection — annular protection or fire dampers may still be required

🔧 Field tip For every vertical duct opening, ask three questions in order: (1) Is this a through penetration, a membrane penetration, or a nonrated floor penetration? (2) What is the assembly rating and how many stories does the duct connect? (3) Does the system operate during a fire? Those three answers determine the shaft, fire damper, CRD type, and fan-control basis. If you can’t answer all three from the drawings, the protection can’t be verified.

Masterbuild QA Lens

The most common and most dangerous error in 607.6 is the static-vs-dynamic CRD mismatch. If the mechanical system is designed to run during a fire — many smoke-control and some exhaust systems are — a static CRD is not listed for that condition and can fail to perform as tested. Before specifying any CRD, confirm the fan control sequence on M-603: does this system operate during a fire event or not? That single answer drives the listing requirement.

Drawing / Submittal Check

For each horizontal-assembly penetration: (1) label the penetration type (through / membrane / nonrated) and the assembly rating on M-101; (2) show the protection method (shaft, floor-line FD, CRD, or IBC 714.5 firestop) on M-501; (3) for the 607.6.1 exception, list all conditions met — steel gage, diameter, single-unit service, continuity to exterior, annular protection, story/area limits; (4) for CRDs, cite the listed assembly and confirm dynamic vs. static against the fan sequence; (5) confirm the number of stories connected — the two-story limit governs whether a shaft is avoidable.

Common Review Risk

Three recurring patterns draw comments: (1) the 607.6.1 small-duct exception applied without showing all conditions (gage, diameter, single-unit, continuity, annular protection); (2) a static CRD specified where the system runs during a fire; (3) a membrane penetration detailed as a standard ceiling opening with no CRD, shaft, or tested-assembly basis. Each is a predictable first-cycle redline.

When To Escalate

Escalate when a duct connects more than two stories (a shaft enclosure per IBC 713 is generally required and the architectural shaft must be coordinated), when the system must operate during a fire (dynamic listing plus smoke-control coordination), or when a tested duct-outlet or membrane-penetration assembly is being relied on and the exact listed configuration must be verified against the field condition.

Rated Assembly Coordination

Horizontal-assembly penetrations are only compliant as part of a complete listed assembly. The floor/ceiling or roof/ceiling rating, the duct material, the damper type and its dynamic/static listing, the annular firestop, and the fan-control basis are a single package — and the listed assembly number ties them together. Missing any one element voids the listing. Run the horizontal-penetration check as a coordinated review across M-101, M-501, M-603, and the architectural life-safety/assembly schedule.