IMC 504 (Part 1): Basics, Penetrations, and Terminations (504.1–504.4.2)

🧠 Plain-English Highlights • 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 in² of open area (no crushed or reduced terminations).

🏗️ 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.

🗺️ Where to show it • M-001: IMC 504 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).

✅ 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.

⛔ 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.