I want to fit a fan in our bathroom. The easiest way to do this seems to be to drill down from the loft and put it in directly above the shower. I'm then considering running the vent (flex pipe) through the loft and tape it to the vents (already in the eaves).

Can anyone say whether this is acceptable, or is it likely to create damp in the eaves?

3 Answers 3


You should use a separate outlet for the pipe as the existing vents won't be able to cope with the volume of air and you'll probably end up with steam in the loft.

Did you buy a kit or separate components?

If you've got a kit then there should be an outlet grille in that, if not you should be able to get one at the same place you bought the fan and flex pipe.

  • Why is this - is it because the steam from the shower will re-enter the loft, or just because the vent will be covered? Commented Aug 18, 2010 at 15:50
  • @pm_2 - the existing vents won't be able to cope with the volume of air and you'll probably end up with steam in the loft.
    – ChrisF
    Commented Aug 18, 2010 at 15:57
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    Interestingly, pretty much all the houses I've been into were built with the fan venting into the attic, which does appear to lead to moisture damage up there. All the good repair guys vent those fans straight to the outside with their own dedicated vent right away, and those moisture problems disappear! Commented Aug 19, 2010 at 17:28
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    @BrianKnoblauch The history seems to be that before [UK] insulation regulations, loft spaces were very open to the wind so it was cheaper and perfectly adequate to ventilate into the loft. However when people started to rockwool their lofts, this setup started causing bad condensation and deterioration of rafters etc. Commented Feb 7, 2020 at 22:08

Through the soffit/eaves is not desirable: Too much moisture can reenter the home and end up in the insulation or attic.

Either through the wall to a wall cap with damper or through the roof with insulated rigid duct to a roof cap. Flex duct is a robber of CFMs (cubic feet per minute, a measure of flow). Try to use a little as necessary and do the main runs in smooth, rigid duct. Save the insulation from your flex duct and put it over the rigid.

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    +1 for the tip of putting the flex duct insulation over the rigid duct! Also, I agree that it's preferable to exit through the gable or roof.
    – Matthew
    Commented Feb 25, 2013 at 22:49

When you say "venting through the eaves", do you mean 1) exhausting throgh a vent in the roof, or 2) exhausting through the soffit (the flat underside of the roof) ?

I like the idea of venting through the soffit, so that no rain can enter the roof if I do a less than perfect job of sealing the vent. But I do not know if this is acceptable.

  • Through the soffit Commented Sep 10, 2010 at 18:14

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