Soil pipe location + vent

[ntl142]

The soil pipe is in an extension on the back of the house. It would previously have been outside. The extension is probably around 15/20 years old, and was present when we moved in 8 years ago.

The soil pipe has had a cupboard built around it, still in the same place but now inside the extension. I have no issues with it but am planning on selling in the future and don't want to find a problem at the time. A couple of questions.

1. The newspaper is blocking up an empty port/connection. What cap should I get to cover it properly? The paper has been there presumably from when it was first fitted. No smells etc.

2. Should it be vented externally? There are no smells etc, no issues with plumbing/draining. Hopefully it's ok as it is because venting externally will be tricky...

Thanks.

 

[jeff the gasman]

An internal rodding eye will cap that nicely 1 1/2” more than likely.
Don’t worry about internal stack.

 

[Harry Bloomfield]

That is an air admittance valve on top. A one way air valve, to let air in, but not let sewer smells out. It avoids the need to have a pipe running outside, up the front wall or through the roof.

Measure the diameter of the hole, to source a blanking plug.

 

[ntl142]

Great news, thanks both. Good to hear it doesn't need to be vented externally, and a plug should be easy to find. Thanks!

 

[ntl142]

Sorry to drag this up. Just found an old document relating to this installation. Can anyone tell me why they've said the AAV has been fitted incorrectly? Thanks.

 

[Hugh Jaleak]

Can anyone tell me why they've said the AAV has been fitted incorrectly?

You've answered your own question in the first line of your original post.

The soil pipe is in an extension on the back of the house. It would previously have been outside.

The soil pipe was originally external and would have vented to atmosphere at roof level, allowing the drains to breathe. Extension has then been built and for whatever reason, (possibly cost, possibly laziness), instead of drains and/or stack being rerouted to continue to vent externally, the soil pipe has been chopped down and capped with the AAV, removing the vent, and effectively sealing the drainage system.

They are asking for the vent to be reinstated, and are saying the new run serving the extension (?) can be terminated with an AAV.

 

[ntl142]

Thanks for the reply. I have a poor understanding of this as you can tell. I thought the purpose of the AAV was to allow air into the drains, and therefore the stack could then be routed internally. Sounds like that's not the case? Would the external soil pipe have also vented to atmosphere, rather than just allowing air in to prevent a vacuum in the drains?

Why would the new run serving the en-suite (put in by previous owners) be allowed to be terminated with an AAV when the soil pipe itself is not?

Just trying to clarify because your reply is at odds to the first two replies above. And then I found this document which flags it up as an issue and I'm asking again.

Thanks.

 

[Hugh Jaleak]

AAV's do exactly that, they admit air into the drains, issues often arise as they wont allow positive pressure out. Your problem is, a former vented stack, that would allow air in and out of the system, has been capped with an AAV, so any positive pressure is not able to escape to atmosphere unobtrusively. What often happens in these situations is, any positive pressure building up in the system looks for the easy way out, usually the shallowest trap, which tends to be a shower. People come on here asking about smells and/or gurgling traps, first thought is usually, have they got a vent or is there an AAV fitted.

Building Regs state the highest point of the drainage system must be vented, if the en suite was connected into the drainage system downstream of the original bathroom, (and assuming there was still the original open vented stack in situ), a second vented stack was not necessary.

 

[ntl142]

Thank you for the really clear explanation. I should have mentioned earlier, it's a single storey cottage, bathroom/en-suite/kitchen all on the same level. In Scotland.

With your help I've done a bit of reading. Have I got this next bit right?


There are two issues to solve. The system must prevent a partial vacuum forming within the drain, and must also be able to vent to outside.

1. This can be solved by one open soil pipe running up the side of the house (lets air in and out) in the conventional way.

2. Or it can be solved by an AAV inside the house (to let air in) but also a vent running externally.

Part H
Ventilated discharge stacks may be terminated inside a building when fitted with air admittance valves complying with BS EN 12380:2002 (with maintenance access, ventilation, etc) I have this already so that's a good start.

and

Discharge stacks should be ventilated. Discharge stacks connected to drains liable to surcharging or near an intercepting trap require ventilating pipes of not less than 50mm diameter connected to the base of the stack above the likely flood level. I'm not sure how you define if a drain is liable to surcharging, or what 'near' to an intercepting trap means, but assuming I do need a vent (?) then a 50mm vent pipe should be sufficient, but what is the 'likely flood level'?


It then goes on to say this, but I think this refers only to stack vents that run up the side of the house (option 1 above):
Ventilating pipes open to outside air should finish at least 900mm above any opening into the building within 3m and should be finished with a wire cage or other perforated cover, fixed to the end of the ventilating pipe, which does not restrict the flow of air.


Am I right in thinking I can keep the AAV, but I must also ventilate externally. This can be done with a 50mm pipe at the base of the stack, above the flood level.

What is the likely flood level?

Many thanks.

 

[Hugh Jaleak]

Am I right in thinking I can keep the AAV, but I must also ventilate externally. This can be done with a 50mm pipe at the base of the stack, above the flood level.

Yes, but ideally use 110mm soil pipe if possible. Do you have any external pipework already?

What is the likely flood level?

Flood level would be the spillover point of the lowest appliance connected to the system, probably either a shower tray or the WC, so i.e. if the drainage system blocks, it will come out at that point and not the vent, which could be hidden and so would not immediately apparent there is an issue until either smell or damp manifests itself.....