Plain English:
504.1 installation: Dryers must be installed per manufacturer's instructions and exhaust to the outside. The only time you skip a duct is for a listed, labeled condensing (ductless) dryer.
504.2 exhaust penetrations:
When the dryer duct penetrates walls/ceilings:
Seal the annular space with noncombustible material, approved fire caulk, or a listed wall box.
Through fire-resistance-rated assemblies, ducts must be proper-gauge galvanized steel or aluminum and the rating must be maintained per IBC.
No fire dampers, combo fire/smoke dampers, or similar devices that obstruct flow are allowed in dryer ducts.
504.3 cleanout: Each vertical riser needs a way to clean lint out (think common/multistory risers).
504.4 exhaust installation
Terminate outside with a backdraft damper.
No screens at the termination (lint trap + blockage risk).
No screws/fasteners that protrude into the airstream.
Do not connect to a vent connector, vent, chimney, duct, or plenum. Dryer ducts are independent.
Seal joints per 603.9.
504.4.1 termination location: If the manufacturer doesn't give a location, terminate at least 3 ft in any direction from openings into the building (including vented soffits).
504.4.2 termination passage size: The outlet must stay full-size and provide at least 12.5 in^2 of open area (no crushed or reduced terminations).
On Plans: Why it matters
A "simple" 4 in dryer duct is one of the most common fire and nuisance callbacks. Screws into the duct, screens at the outlet, or badly detailed penetrations through rated walls are easy redlines.
Code Path: Where to show it
M-001: IMC 504 clothes dryer exhaust note (outdoor discharge, no screens, no screws in airstream, no fire/smoke dampers, min 3 ft from openings when not specified by manufacturer).
M-101: Show routing, rated penetrations, and dimensioned termination clearances to doors, windows, and soffit vents.
M-601: Dryer exhaust line in the schedule with duct size, material, termination type, and code ref (IMC 504.1-504.4.2).
Check: Do
Ask early: vented dryer or listed ventless unit?
Coordinate penetrations through rated walls/ceilings with architect and FP so the rating is clearly maintained.
Review Risk: Don't
Show screens, louvers, or "bug covers" over dryer terminations.
Put fire/smoke dampers or protruding screws in dryer ducts.
Tie dryer exhaust into chimneys, vents, or plenums.
Field Tip:
Add a standard "DRYER EXHAUST (IMC 504)" keynote that calls out: Ø in smooth metal duct, discharge outside with backdraft damper, no screens, no screws, no fire/smoke dampers, min 3 ft from openings where the manufacturer is silent. It keeps every project consistent and speeds review.
Masterbuild QA Lens
Dryer exhaust duct material is one of the most-cited residential mechanical comments. Confirm the duct is rigid metal (smooth interior), not flexible plastic or aluminum foil, and that any flexible transition at the dryer is UL 2158A-listed and under 8 ft. The duct material must be stated on the schedule or detail - not left to the installer.
Drawing / Submittal Check
Dryer exhaust duct routing must be shown on the drawings with each duct segment dimensioned or scheduled. Show duct penetrations through fire-rated assemblies with the required protection method (sleeve, not a fire damper - IMC 504 prohibits fire dampers in dryer exhaust). Note the exhaust termination location, clearances from openings, and the required backdraft damper at the termination.
Common Review Risk
Fire dampers in dryer exhaust are prohibited by IMC 504 but frequently shown by non-specialized designers. A fire damper in a dryer exhaust duct will accumulate lint, restrict airflow, and ultimately fail. Confirm that no fire dampers appear in the dryer exhaust duct routing, even through fire-rated assemblies. Sleeve penetrations with the required clearance are the correct detail.
When To Escalate
Escalate when the dryer exhaust duct must penetrate a fire-rated assembly and the required sleeve penetration conflicts with the structural system or the fire rating of the assembly. Dryer exhaust penetration conflicts in high-rise residential buildings are a common source of field coordination problems that should be resolved in design, not in the field.
Rated Assembly Coordination
Clothes dryer duct penetrations through fire-rated walls and floor-ceiling assemblies require a listed penetration firestop or damper. Show the penetration detail at each rated assembly crossing and confirm the dryer duct backdraft damper meets the rated assembly requirement.
Duct System Coordination
Clothes dryer duct basics include material type (smooth metal), minimum diameter, and how the duct penetrates the building envelope. Wall penetration detail and backdraft damper spec belong on the duct drawing.