Bathroom vent dripping water
moderate 1–3 h
Tools: flashlight, screwdriver, tape measure, utility knife, foil tape · Materials: insulated flexible duct (R-6 or better) or a duct insulation sleeve, exterior vent cap with a backdraft damper, hangers or strap
Steps
- Time the drip: water during or right after a shower on a cold day is condensation; water during rain is the roof or wall cap leaking.
- Go into the attic and follow the duct from the fan: a bare metal or thin foil duct sweating in winter, a sag where water pools, or a duct that ends in the attic tells you the cause.
- Reroute the duct as short and straight as possible, rising steadily from the fan to the outlet so any condensation drains back to the fan housing and evaporates, not into a low loop.
- Wrap the whole run in insulated duct or a sleeve, tape the joints with foil tape, and support it every metre so no bellies form.
- If the duct ends in the attic, run it through the roof or a gable wall with a capped, dampered outlet; venting into the attic feeds mould.
- Run the fan for 20 minutes after every shower — a timer switch makes that automatic — and confirm the damper flap at the outside cap closes freely.
Stop and call a pro if
- the drip appears during rain or there is a stain spreading beyond the vent — the roof penetration or flashing leaks
- the attic is unsafe to move through (no flooring, vermiculite insulation, knob-and-tube wiring)
- the fan is wired without a box or the wiring is damaged
What a pro does that you can't
An HVAC contractor reroutes the duct through the roof with a proper flashed cap, sizes a fan that clears the room in 20 minutes, and a roofer fixes a leaking penetration.
DIY cost: $25–70 in insulated duct, tape and a cap