/ Field knowledge · IMC 601.3
A stair fan is not a toilet-exhaust tap.
An exit enclosure is a protected egress path — usually an interior exit stair or ramp in fire-resistance-rated construction. IMC 601.3 is not comfort HVAC. Ventilation serving that space has to follow one of three permitted arrangements, stay independent of other building ventilation, and keep openings limited and protected. Tying a stair fan into general HVAC is the usual redline.
Educational 2024 International Mechanical Code (IMC) 601.3 from Daily Code Talk. Confirm the adopted edition and the International Building Code (IBC) shaft and opening-protection path. Distinct from dampers (607) and 601.4 contamination. This is not a stair-pressurization design.
- Item 1: equipment and ductwork outside the building, connecting directly to the exit enclosure through ductwork enclosed as required by the IBC for shafts.
- Item 2: equipment and ductwork within the exit enclosure only where intake is taken directly from outdoors and exhaust discharges directly outdoors, or those air paths are routed through IBC shaft-enclosed ductwork.
- Item 3: equipment and ductwork in the building but outside the exit enclosure, separated from the rest of the building — including other mechanical equipment — with construction as required by the IBC for shafts.
- Openings into fire-resistance-rated construction limited to those needed for operation and maintenance, protected with self-closing fire-resistance-rated devices per the IBC. The exit-enclosure ventilation system is independent of other building ventilation systems.
On the set: which 601.3 path, intake and discharge to outdoors explicit, shaft ratings and opening protection coordinated with architectural life-safety, airflow diagram, and controls sequence. Do not leave intake or discharge routing vague. Do not penetrate rated construction without showing the required protection.
A stair exhaust tapped off the toilet-exhaust riser
Or a rooftop unit serving the stair and the corridor on the same system. Independence is the rule. If the drawings cannot name which of the three items is used, the system has not been designed for 601.3.
Source: Daily Code Talk — IMC 601.3 · tool: Exit-enclosure screen · 607: dampers · partitions: 607.5.3.
What to send
Life-safety / stair plan, the fan serving that enclosure, and whether intake and discharge are shown to outdoors on their own system.
If the stair fan is on the general HVAC
Send the life-safety plan and the fan. Masterbuild will say whether 601.3 still has no independent path — or 607 still has a damper type miss at the enclosure.
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 three 601.3 arrangements and independence from other building ventilation are 2024 IMC 601.3 education from Daily Code Talk — not a stair-pressurization or smoke-control design. This page is not legal advice.