Rain water leaks through bathroom extractor fan.

Posted 2nd Oct 2022
Hi everyone, few days ago, rain water leaked through fan vent and tripped the fuse switch.

I investigated how the water leaked and tried to replicate water leak by pouring few liters of water around and top of vent cowl but it did not leak.

See attached photos with explanation. Any ideas/thoughts of how this happens?.Photos (please click this link and turn the phone around to landscape view or select desktop layout to view photos. For some reason, I cannot upload photos directly).

Further info: In last 3 years, I had to replace the fan twice and electrician said, water marks in fan and it is shorting the electrics. I was thinking it may be accidental as water got in with wind and water marks were very minor. However, few days ago, lots of water came through. Temperature dropped last week so I don't know if it is something to do with it.

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  1. Avatar
    Would suggest carefully removing the moss from your flat roof.
    Thanks. Never thought of it before but will get that done as well. I assume moss attached to stone chips so should come off easily. Any tips?.
  2. Avatar
    Condensation plausible.
    No indication of checks on how power is delivered. Is it possible for water to capillary in / around / via power supply cabling?
    Thanks, I will look into capillary in scenario. It is not condensate (cloakroom and about 300ml water came through).
  3. Avatar
    Could be it’s condensation in pipe check this


    The fan should have a run on timer on it (edited)
    I would say about 300ml of water came through. The vent pipe is about 2m long straight up vertical. It seems too much water for it to be condensate. Yes the fan had timer on it. Also this is cloakroom, no shower or bath facilities.
  4. Avatar
    Has your cowl got cracks on top ?
    No it doesn't. I checked it.
  5. Avatar
    It's condensation not rain water. Either have ducting replaced with insulated or you may find its drooping and just needs little maintenance.

    It's basically collecting.in.the ducting and when there is too much it's coming back in on itself.

    The massive change is temperature is what created it.
    About 300ml water came through and this is cloakroom. Vent pipe is 2m long straight up vertical. I can't think it being condensate water. (edited)
  6. Avatar
    Are you sure the rain is not getting in through the flashing, running over the boarding then down through the hole for your vent tube?
    I have added another photo of roof in the link. There is flashing on the left side of this flat roof against house wall. I assume what you saying is that the water could be getting below felt (top roof material) somewhere along this flashing but top of another layer, runs towards vent pipe and then comes down through the outside of vent pipe. Is that what you mean?. Yes that sounds a realistic scenario. I will look into this. Thanks. (edited)
  7. Avatar
    I thought condensate, but you seemed to have ruled that out, also capillary is plausible. There could be wicking from another point in the roof - the water will then wick down to the lowest point...
  8. Avatar
    The flashing could have crack along it same happened to my roof water came in at a different place from crack
    Good point. I added another photo. Yes there is flashing on one side of this flat roof against house wall. I will check for any damage. How did you fix your crack?. Thanks.
  9. Avatar
    I'd switch fan to centrifugal and see if the air flow stops the problem.
    Can't say for sure but that dont look like a centrifugal fan?
    I think it's not pushing enough air through and out so condensation if forming.
    If standard fan that cowling with stop the airflow (edited)
  10. Avatar
    How old is the roof?
    I would think about 20 years.
  11. Avatar
    I always wanted a water feature! 🤪
  12. Avatar
    Trouble with water leaks is where you see the water coming though inside is not necessarily where it entered outside.
    Flat roofs are always problematic too
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