/ Field knowledge · IMC 504
No screens. No screws in the airstream. No damper.
A 4-inch dryer duct is one of the most common fire and nuisance callbacks. Screens at the outlet, screws in the airstream, and fire dampers in dryer ducts are easy redlines.
Educational 2024 IMC 504.1–504.4.2. Confirm the adopted edition and the manufacturer’s instructions. This is not a dryer-duct design.
- 504.1. Exhaust to the outside unless it is a listed condensing (ductless) dryer.
- 504.2 penetrations. Seal the annular space. Rated assemblies: proper-gauge steel or aluminum and maintain the rating. No fire damper or combination fire/smoke damper in a dryer duct.
- 504.3. Each vertical riser needs a lint cleanout (multistory).
- 504.4. Outside termination with a backdraft damper. No screens. No fasteners protruding into the airstream. Independent of vents, chimneys, plenums.
- 504.4.1. If the manufacturer does not give a location, at least 3 ft in any direction from openings into the building — including vented soffits.
- 504.4.2. Outlet stays full size and at least 12.5 in² open area. No crushed boots.
Source: DCT 504 Part 1 · general exhaust: 501.3 · tool: dryer check.
What to send
Unit count (dwelling vs common riser), routing through rated walls if any, and the termination location relative to windows and soffits.
If the dryer duct is “just a 4-inch flex”
Send the routing and the termination photo or elevation. Masterbuild will say whether 504 is a drawing note or a rated-penetration problem.
Send Project Background+1 (786) 398-6940 · osmany.portal@masterbuildconsulting.com
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