Dryer vent & roof deck gap

[Jack Wingo]

House was built in 1999 and roof covering replaced in 2017. There's an open gap between the clothes dryer vent duct and roof sheathing. Did code require sealing gap at time of construction or when re-roof? If so, what is the code?
Thank as always for your help
Jack

[Jerry Peck - Codeman]

Jack,

For a dryer vent, versus a Type B Gas Vent, there are no minimum clearance requirements (a Type B Gas Vent has a minimum of 1 inch clearance to combustible material).

For a dryer vent, there are no maximum sizes either, as long as the flange of the exhaust cap on the roof adequately covers it for flashing purposes.

Keep in mind that the minimum clearance for a Type B Gas Vent is 1 inch, which that looks to be less than, so it is likely not 'too large' of a gap - but the only way to know would be to the size of the flange on the roof cap.

[Jack Wingo]

Jack,

For a dryer vent, versus a Type B Gas Vent, there are no minimum clearance requirements (a Type B Gas Vent has a minimum of 1 inch clearance to combustible material).

For a dryer vent, there are no maximum sizes either, as long as the flange of the exhaust cap on the roof adequately covers it for flashing purposes.

Keep in mind that the minimum clearance for a Type B Gas Vent is 1 inch, which that looks to be less than, so it is likely not 'too large' of a gap - but the only way to know would be to the size of the flange on the roof cap.

Jerry,
I was under the impression, the gap can allow a build up of lint and also reduce the exhaust velocity. Why do I see all on new construction the dryer duct penetration sealed?

[Jerry Peck - Codeman]

I was under the impression, the gap can allow a build up of lint and also reduce the exhaust velocity. Why do I see all on new construction the dryer duct penetration sealed?

Jack,

The gap I am referring to is the gap between the outside of the dryer duvt and the roof shearing.

The dryer duct is supposed to be sealed all the way, including to the cap through the roof.

If the dryer duct is not sealed to the cap, there would be lint all over around the end of the duct - check to make sure it is sealed to the cap.

[Jerry Peck - Codeman]

Jack,

I was looking at your photo on my phone before, back at my office on my computer, zooming in 400%, and I see the metal roof cap exhaust vent showing up past the plywood roof sheathing.

That indicates that the dryer duct is 'just shoved up into' the exhaust vent roof cap, but the dryer duct and the exhaust roof cap are not sealed to each other, and I see what might be some lint at the top of the dryer duct (but not what I have typically seen with dryer duct/exhaust vent roof cap connections like that - maybe that was recently cleaned?

Regardless, the dryer duct is to be sealed to the exhaust vent roof cap.

[Jack Wingo]

Jack,

I was looking at your photo on my phone before, back at my office on my computer, zooming in 400%, and I see the metal roof cap exhaust vent showing up past the plywood roof sheathing.

That indicates that the dryer duct is 'just shoved up into' the exhaust vent roof cap, but the dryer duct and the exhaust roof cap are not sealed to each other, and I see what might be some lint at the top of the dryer duct (but not what I have typically seen with dryer duct/exhaust vent roof cap connections like that - maybe that was recently cleaned?

Regardless, the dryer duct is to be sealed to the exhaust vent roof cap.

Jerry,
Is there a code that requires dryer duct to be sealed?

[Jerry Peck - Codeman]

Is there a code that requires dryer duct to be sealed?

Yes, and one is not so obvious and specific, with another which is in a more obvious and specific way.

(underlining is mine)
- SECTION M1502
- - CLOTHES DRYER EXHAUST
- - - M1502.1 General.
- - - - Clothes dryers shall be exhausted in accordance with the manufacturer’s instructions.
- - - M1502.2 Independent exhaust systems.
- - - - Dryer exhaust systems shall be independent of all other systems and shall convey the moisture to the outdoors.
- - - - - Exception: This section shall not apply to listed and labeled condensing (ductless) clothes dryers.
- - - M1502.3 Duct termination.
- - - - Exhaust ducts shall terminate on the outside of the building. Exhaust duct terminations shall be in accordance with the dryer manufacturer’s installation instructions. If the manufacturer’s instructions do not specify a termination location, the exhaust duct shall terminate not less than 3 feet (914 mm) in any direction from openings into buildings. Exhaust duct terminations shall be equipped with a backdraft damper. Screens shall not be installed at the duct termination.
- - - - - [Jerry's comment: The not so obvious/specific one - not sealing the dryer duct to the dryer exhaust cap, which is part of the dryer duct run, allows the clothes dryer exhaust to: a) 'terminate inside the building', which is not allowed; b) not sealing the dryer duct to the dryer exhaust cap creates an opening and the dryer duct is terminating less than 3 feet from an opening into the building ... the opening within the dryer exhaust cap and around the dryer exhaust duct.]
- - - M1502.4 Dryer exhaust ducts.
- - - - Dryer exhaust ducts shall conform to the requirements of Sections M1502.4.1 through M1502.4.7.
- - - - M1502.4.2 Duct installation.
- - - - - Exhaust ducts shall be supported at intervals not to exceed 12 feet (3658 mm) and shall be secured in place. The insert end of the duct shall extend into the adjoining duct or fitting in the direction of airflow. Exhaust duct joints shall be sealed in accordance with Section M1601.4.1 and shall be mechanically fastened. Ducts shall not be joined with screws or similar fasteners that protrude more than 1/8 inch (3.2 mm) into the inside of the duct.
- - - - - [Jerry's comment: The more obvious and specific one - not sealing the dryer duct to the dryer exhaust cap, which is part of the dryer duct run, creates a joint which is not sealed. Even this is not that obvious to many contractors as they do not think of the "joint" in the dryer duct run at the dryer exhaust cap as a "joint" ... possibly because they did not "join" the two together, they just 'stuck one into the opening' of the other.]