/ Field knowledge · IMC 512.5
A transfer grille across a smoke barrier with no damper will not hold ΔP.
Smoke control only works if the barrier is real. IMC 512.5 is tightness and openings: leakage-area ratios, door protection, and required smoke dampers at transfer paths. Walls: A/Aw = 0.00100. Interior exit stairs, ramps, and exit passageways: A/Aw = 0.00035. Enclosed exit-access stairs/ramps and other shafts: A/Aw = 0.00150. Floors and roofs: A/AF = 0.00050. Those ratios do not include door gaps or operable windows. Ducts and transfer openings through smoke barriers need a minimum Class II, 250°F smoke damper. A transfer grille across a smoke barrier with no damper is the commissioning failure.
Educational 2024 International Mechanical Code (IMC) 512.5 from Daily Code Talk. Confirm the adopted edition. Pair with 512.6 ΔP and 607 dampers. This is not a smoke-control design. A = leakage area; Aw = wall area; AF = floor area.
- 512.5: smoke barriers meet IBC 709 and stay within those maximum leakage-area ratios. Door gaps and operable windows are added separately (512.5.1 total leakage = gross barrier area × ratio + openings).
- 512.5.2 testing: pressurization systems show compliance by achieving the required ΔP across the barrier in smoke mode. Passive systems: door-fan testing or another approved method.
- 512.5.3: openings in smoke barriers need automatic-closing devices tied to smoke control. Doors must be compliant smoke-barrier door assemblies (IBC).
- 512.5.3.2: ducts and transfer openings through smoke barriers require a minimum Class II, 250°F smoke damper (per IBC). Corridor returns that jump the barrier without a damper will not hold 0.05 in. w.g.
On the set: life-safety sheets with smoke-zone extents and every door at the barrier. Door schedule: smoke-barrier door + automatic-closing method. Mechanical: every duct/transfer opening tagged with a smoke damper. Smoke-control report: leakage assumptions so the ΔP math matches construction.
A corridor return that jumps the smoke barrier with no damper
Trace each smoke barrier and count every opening. If an opening is not tagged with a protection method, expect a commissioning failure. Leakage-area calcs belong in the permit set — not only in an external report.
Source: Daily Code Talk — IMC 512.5 · tool: Barrier-opening screen · methods: 0.05 in. w.g. · hardware: 512.10 · 607: dampers.
What to send
The life-safety sheets showing smoke-barrier extents, a door schedule at those walls, and whether every duct/transfer opening is tagged with a smoke damper.
If a transfer grille crosses the smoke barrier with no damper
Send the life-safety and M sheets. Masterbuild will say whether 512.5 still has no Class II 250°F damper — or 512.5 still has leakage ratios only in a report the reviewer cannot see.
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. A/Aw 0.00100 / 0.00035 / 0.00150, A/AF 0.00050, and Class II 250°F smoke dampers at ducts/transfers are 2024 IMC 512.5 education from Daily Code Talk — not a smoke-control design. This page is not legal advice.