Protection Requirements for a Dryer Vent Penetrating a Roof

[jar546]

Scenario:You have a residential dryer on the top floor of a building. The roof is a 1-hour rated concrete structure. The dryer duct is 4-inch steel and will route directly from the dryer through the roof. The plan is to wrap the dryer duct with 1-hour rated duct wrap and route it up through the roof without a fire damper.

Question: Does wrapping the dryer duct with rated wrap qualify as an acceptable enclosure for exception #1 of 2015 IMC Section 607.6.1 for ducts located in the cavity of a wall?

Opinion: This opinion also applies to the 2018, 2021, and 2024 IMC.

2015 IMC Section 607.6 is not applicable in this case. This section addresses the penetration of a ceiling membrane of a roof/ceiling assembly and not a fire-resistant rated concrete surface.

For a residential dryer venting through a fire-resistant rated concrete roof, the ductwork must meet the minimum thickness requirements specified in Section 603.4. Section 504.2 requires clothes dryer ducts to be constructed of galvanized steel or aluminum of the thickness specified in Section 603.4. Additionally, the minimum thickness requirement of Section 504.8.1 applies if the dryer is a residential dryer.

It is important to note that the annular space provision of Section 504.2 does not apply to this condition because it applies when the ceiling membrane of a roof/ceiling assembly is penetrated, not when a fire-resistance rated concrete deck is penetrated.

 

[steveray]

This got screwed up when they moved all of the horizontal assemblies around IMO.......If it is a rated structural roof IA,IIA...whatever....who cares if the fire gets through a penetration and burns....the sky? If it is separating occupancies or tenants, I completely agree...

 

[mtlogcabin]

504.2 Exhaust penetrations.
Where a clothes dryer exhaust duct penetrates a wall or ceiling membrane, the annular space shall be sealed with noncombustible material, approved fire caulking or a noncombustible dryer exhaust duct wall receptacle. Ducts that exhaust clothes dryers shall not penetrate or be located within any fire blocking, draft stopping or any wall, floor/ceiling or other assembly required by the International Building Code to be fire-resistance rated, unless such duct is constructed of galvanized steel or aluminum of the thickness specified in Section 603.4 and the fire-resistance rating is maintained in accordance with the International Building Code. Fire dampers, combination fire/smoke dampers and any similar devices that will obstruct the exhaust flow shall be prohibited in clothes dryer exhaust ducts.