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Discuss Routing output from bathroom fan condensation trap? in the DIY Bathroom Remodelling Advice area at

Hi. I've got a vertically-installed fan in the wetroom. Want to add a condensation trap to it as the vertical vent pipe goes through a cold flat roof. My question is, can I route the outlet from the condensation trap back into the wetroom through a ceiling fitting? Access to the soil stack from where the fan is already installed is not possible. Also, as it's an enclosed wetroom with no outside walls, routing it to a side wall isn't possible. The roof is a flat roof - so no crawl access above either.

Thanks for any advice.


You say it’s a flat roof . which way do the joists run? And could you not follow the path of least resistance to the outside?

You also need to be aware that not fans are suitable for such a vertical vent pipe and ceiling mounting


Hi. No pictures - just a hole in a ceiling where the fan went. Have added a drawing below trying to show what I was thinking?

I was hoping the path of least resistance would be to simply angle the waste pipe from condensation trap down into the wetroom (marked 'output' below). The nearest external wall to the vent is accessible along a joist run, but that wall makes up part of my neighbour's garden. I would also have to either tunnel through the celotex between the joists which would compromise the insulation layer, or lay the condensation trap outlet pipe within the narrow air gap between flat roof covering and insulation.

The vent I've got 'vent-axia VSF100' and can operate vertically. Just need to protect it with a condensation trap.



It wont work, the condensate outlet needs to be fitted to a horizontal section of pipe so that the water runs into it.

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