Often, when I see a dryer vent vertically out the roof, the vent termination cap has a wide grill and a cap over it. Often, they are clogged or partially clogged.
The 2006 IRC states: “Exhaust duct terminations shall be equipped with a backdraft damper. Screens shall not be installed at the duct termination.”
If you are familiar with what I’m talking about, those vents through roofs, do you think they meet the definition above? (To me a damper is a flap device and I don’t think they have them.)
Photo: Dryer vent is right side of plumbing vent.