12 Jul 2016
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United Kingdom

I previously thought I had a problem with leaking ventilation ducting from an extractor fan vent in the loft caused by steam from the shower fan and/or a leak in the roof.

This originally started as a nail had pierced the flexible ducting used to connect the 2 pipes in the loft and water was building up in the ducting as the ducting wasn't well insulated and very loose fitting (running horizontal in sections).

I've now established that this is actually a soil vent pipe after removing the ducting as we were still getting a leak into the bedroom ceiling below even after making sure the roof was sealed and not using the extractor fan at all.

It sounds and looks very similar to this issue experienced by someone else:

Is it possible that the extractor fan for the shower could be connected into the soil vent pipe? They are in close proximity and I can't see anywhere else obvious where the extractor fan would vent via.

From an initial look online I think there are 3 possible solutions, although please let me know if there might be more!

- 1) replace the cheap looking non-insulted ducting (which was patch repaired due to the nail puncture) with better quality ducting designed for soil venting. And reduce any horizontal sagging. Might be difficult through as there is nothing to support the ducting between the 2 pipes.
Can anyone recommend any good ducting for this? Think it's 100-110mm diameter and will need to be 1.5-2m long.

- 2) Fit an air admittance valve on top of the soil vent pipe with no connection to the roof vent. I'm confident that no water will enter from the roof. Possibly something like this
However I'm not sure if this would cause any issues with excess moisture needing to escape, especially if the shower extractor fan was connected to the soil vent pipe?

- 3) Get a plumber (or possibly try myself) to fit solid angled pipes between the roof pipe and soil vent pipe in the loft. The issue with this is access in the loft. It's an extension loft which is extremely difficult to access with a real risk of putting holes in the ceilings trying to get to the location and very tight space to work in.

My preference would be option 2 because it seems the easiest to do but I'm not sure if it is the best solution. Also would the valve require regular maintenance which wouldn't be ideal (but possible) due the access issues.

Any advice would be much appreciated.

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Firstly, I strongly advise you do not remove any existing vent for the soil pipe. Ventilation for the drainage system is required under Building Regs, and blocking it off could open up a whole new world of issues with smells, gurgling traps, etc. Drains need to breathe! Secondly, if the extractor is connected to the soil pipe, last thing you want to do is cap that off!

Possible there is water ingression from the vent during rainfall, are there any dips in the pipework where water could collect? Unusual for soil vent to run any further than need be, usually it would be taken up to and through the roof with the shortest possible route.
Thanks for the reply.

I had another look and I'm sure the extractor fan is actually separate from the soil vent pipe.

I take your point about the potential drawback of option 2, fitting an air admittance valve. That it would restrict the drains being able to fully breath.

I had a look at screwfix and found a couple of pipe fittings that might solve the issue. Hopefully they should be pretty straightforward to fit. It sounds like it just needs some lubricant and they can be pushed into place.

I could try fitting 2 of these on each of the existing pipes: the top of the soil vent and bottom of the roof vent pipes. This should allow me to flex them into the ideal position.

And then connect a 1m pipe between the 2 of them, say one like this

That's probably the best solution given the situation?
Sounds like a plan, should sort the matter out. Just make sure the pipework is supported properly, and remember the ends of any pipes will need chamfering before you attempt to push a fitting on, or you'll displace the seals.
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Thanks for the tip. Never done anything like this before so any tips welcome!

Can I just use washing up liquid to lubricate between the pipe and adjustable bends? Or do I need a special lubricant?

How far would you normally need to insert a pipe into these fittings?

I'm thinking in terms of if I'll have enough pipe. The gap is probably 1.2-1.3m, with the pipe 1m in length. The 2 adjustable bends should add an extra bit to reduce that gap as well. It's either going to fit perfectly or I might be short by a fraction.

If I'm short a fraction is there any tape or seal etc I could apply to secure the top of the new pipe to the bottom of the adjustable bend I'll fit to the bottom of the existing pipe going to the roof vent?

Dont 'make do', buy enough pipe to do the job, a 3m length is only another £8. You want it air and watertight, or it's a waste of time doing anything. Insert the pipe until it hits the 'stop', if the seal is lubricated and the spigot end chamfered nicely, the pipe will slide home without much effort.

You're not supposed to use washing up liquid, but for just 4 joints, it's not worth spending £8 on a pot of lubricant you'll probably never use again.
The solution I described above won't work based on the vertical height and angles between the top of the soil vent pipe and the bottom of the roof vent pipe.

It just won't fit.

The only solution is either to fit an air admittance valve on top of the soil vent pipe with no connection to the roof vent (option 2 above). However based on the comments above this probably isn't advisable as the drains won't be able to properly breath.

This means I'll need to find some kind of flexible ducting to connect between the top of the soil vent pipe and the bottom of the roof vent pipe.

However I can't seem to find anything suitable that is at least 1.3-1.5m in length.

Any suggestions would be really helpful as I've reached a bit of a dead end!

Can you do from the SVP up in solid pipe then use a smaller section of flexi for the final connection?

If you can get close enough you could make you connection with a bandseal (rubber connector with jubilee clips).
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125mm aluminium extractor ducting will fit over 110mm soil, obviously loosely but with a decent overlap, a bit of manipulation and duct tape it can be made air tight:

This is for my extractor fan (I used plastic in the boarded area of the loft so it doesn't get squashed and changed to aluminium so I could bend it to reach the eaves. It is light enough and self-supporting to span between your pipes, as it's vertical you could also secure each end with a large jubilee clip - belt and braces.
Also I don't understand where water is coming from - it should have a mushroom on top.
Some interesting suggestions although I didn't even think about aluminium ducting for a soil vent. I just assumed it wouldn't be suitable and durable for this purpose.

Hugh - that flexi pipe is only 480mm. My gap is around 1.4-1.5m. I've struggled to find anything advertised as suitable for soil ducting in that length.

I have also posted on the screwfix forum and a strong suggestion is to use an air admittance valve instead, which does sound like a much simpler solution. Unless any strong arguments against this I think I'll go with an AAV?

Please see response below from one of the responders regarding AAV:

I consider AAVs as being fit-and-forget, i.e. I have never serviced one or even felt the need to. The oldest one I have was fitted 29 years ago and I still hear the very faint tell-tale rumble as it does its job. I would only feel the need to service it if I didn't hear it working. When working correctly they would NOT allow any moisture in your loft. Moisture would be the same as smell, which is exactly what they're designed to prevent. In all the situations where I have used them, they are the only vent for the soil stack, and I have never had a problem with them. In fact, thanks to having one, I was able to detect a partial blockage in my sewer line earlier than if I had an open stack because the toilet was slightly slower in emptying than normal. It was slower because the flush wasn't able to push the air forward (because of the partial blockage) and it also couldn't push the air backwards (because of the AAV). The sewer would have to have been completely blocked before I noticed it had I had an open stack, and that would have made it much harder to clear.
Can you put up a picture of what you are trying to achieve please? Will be better able to advise perhaps if we can see what you're faced with.

AAV's have their purpose and place, and if you choose to fit one, then that is your prerogative. I am merely trying to point out the possible pitfalls of doing so, and negate the chance of you to then come back asking why you have a different set of problems. It is entirely possible you could fit an AAV and have no problems, in which case, fine. If however, you start to experience issues with bubbling/gurgling traps/WC's due to issues within the drainage system, then you'll be back to the drawing board.

Drains need to breathe, so for this very reason, the Regs have guidance on ventilation requirements. If you want to read up, they're available here: https://assets.publishing.service.g...achment_data/file/442889/BR_PDF_AD_H_2015.pdf
Can you get that in paper form Hugh?

I’m amazed that i’ve never read it!!
Thanks for sending that on Hugh. I tried to read it on my phone which probably isn't the best idea as there is a lot of info in it.

Ian - just print off the pdf from the link and save paying £14 on ebay.

Hugh - it's hard to fit everything into 1 photo so I've posted this short video.
Ignore all the empty chocolate tubs - ha ha. And the pipe bend on top of the soil pipe on the right hand side was just placed on top to see if it would help. This is an open soil pipe coming up completely vertically with no bend.
The pipe coming down goes straight through to the roof vent mushroom cowl.
As mentioned the distance between pipe ends is about 1.4-1.5m with minimal vertical distance, maybe 0.5m.

Ignore my comment about water coming in from the roof. I don't think this is a problem anymore after fitting the mushroom cowl. Do you think an AAV would work well here?

There is quite a bit on insulation material dust but only when you move around. It should be settled when no one is up there.

I was thinking of trying this AAV? Thanks again for your help

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