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Rain water getting inside bathroom exhaust vent pipe - no sign of roof leak

Rain water getting inside bathroom exhaust vent pipe - no sign of roof leak


Old 11-16-17, 10:14 PM
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Rain water getting inside bathroom exhaust vent pipe - no sign of roof leak

during heavy rainstorm last night water came dripping into bathroom through exhaust fan. Checked in attic and found no signs of water coming in through roof but found about an inch of water inside the flexible ducting going from roof to exhaust fan.

Patched this area last winter and had no leaks at all during rainy season, and we had a lot of rain.
How could water be getting into the pipe but not leaking into atttic from roof?

Last edited by Stumped1; 11-16-17 at 10:15 PM. Reason: correction
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Old 11-17-17, 02:44 AM
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Condensation has probably been accumulating inside the pipe for some time, especially if the duct goes straight up. Of course without knowing or being able to see how it's hooked up, whether it actually goes to a roof louver or is just hanging free near the exhaust fan, it's hard to say.

But your exhaust fan will pull in cool damp air, cooling the duct, while any humidity from the bathroom will condense on the inside of the cold duct. It has nowhere to go but down.

It's always best if bath fans are kept low, between the joists where they can be buried in insulation and kept warm as possible, then attached to a roof louver very low on the roof... maybe within 2 ft of the gutters. (Not way up by the ridge or directly above the bath fan).

Checking ductwork for standing water should be part of a regular maintenance routine if this is a problem.
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