Why is water coming through my roof vent?
Short answer. When water comes through the vent itself rather than around its base, the usual causes are wind-driven rain blowing into a box vent or ridge vent, condensation forming inside a bath fan duct and running back down, a missing or stuck damper on an exhaust cap, or a hood cracked or dented by hail. Turbines that have stopped spinning can also let rain in.
Separate the possibilities
- Wind-driven rain: drips only in storms from one direction, often under box vents on the side facing the storm, or under an unbaffled ridge vent. Fixed with baffled vents or by replacing older styles.
- Condensation in exhaust ducts: water at the bath fan grille or on the ceiling around it, worst in cool weather after showers. Warm, wet air cools in an uninsulated duct, condenses, and runs back down. Fixed with insulated duct, a shorter run, and a cap with a working damper.
- Damper missing or stuck open: rain and cold air come straight down the duct.
- Damaged hood: hail dents or cracks plastic and thin metal vents, and an opened seam leaks in every rain.
- Stalled turbine: a seized turbine head can sit with its fins open to rain.
- Melting frost: in winter, frost that formed inside the vent or on nearby nails melts and drips.
Clues from timing
Water only during heavy, windy storms points to rain intrusion. Water on dry days after showers points to condensation. Water on sunny winter mornings points to frost. A quick log of dates and weather narrows the cause faster than anything else.
What fixes it
Rain intrusion is fixed at the roof: a better vent, correct placement, or a new hood. Condensation is fixed in the attic: insulate and shorten the duct, seal the joints, and make sure the fan actually reaches the outside. If hail damaged the vents, look at the shingles and gutters too, since dented vents are often part of wider storm damage. See common roof leak causes and roof ventilation basics.