Extension WC connections

[BuildingNovice]

We have a WC in a bathroom in a rear single storey extension, which also has a kitchen.

The soil pipe for the WC is vertical into the bathroom floor and drains into the underground sewer chamber next to the property (which I beleive is about 2m below ground). The WC is against an external wall to the side alley where the manhole for the sewer is.

I believe the kitchen sink waste connects to the same sewer chamber (or possibly to the WC discharge pipe).

My builder has put in a new ventilation pipe (VP) which comes out of the ground in the shared alley and runs up the extension wall and bends over side door to connect to the VP attached to the main house (latter pipe is also the pipe used to discharge waste from house WC)

This new VP is very unsightly and i'm thinking what options there may be to remove it and do something else instead.

I beleive the new VP cannot be shortened and capped with an air admittance valve, as latter cannot be used externally?

Could WC soil pipe be taken horizontally through wall instead and connected to this ventilation pipe (which I suppose would then become a discharge pipe) - my reading of the regulations is this may be OK if the slope is low enough. However, this would mean the kichen waste loses ventilation?

Any help much appreciated

 

[Richard C]

You can actually get AAAV's suitable for externally use but they can only be used if the foul drain system has another open vent for positive ventillation.

Bit confused by what you mean with the term VP & what exactly has been done & why, can you provide a sketch or photos? May be able to suggest something from that.

 

[BuildingNovice]

Richard,

Thanks for your response and sorry for the lack of clarity (VP was shorthand for ventilation pipe).

It may be better if I ask some direct questions instead:

The WC in a ground floor extension connects to a vertical soil pipe located directly underneath it coming out of the bathroom floor, and this soil pipe connects via a right angled pipe directly to an inspection chamber less than 1m away horizontally in a side alley next to the extension. The chamber is less than 1/2 metre below level of bathroom floor.

In these circumstances does the connection to the WC need a ventilation pipe (to avoid loss of water seal) ?

The above mentioned inspection chamber connects via a short pipe to a lower (about 2m) older brick chamber, which is ventilated to outside (via soil stack to main house). Would the new, higher inspection chamber need ventilation to outside? I wouldn't have thought so as gases under pressure would have an escape route already via house stack.

 

[Richard C]

VP was shorthand for ventilation pipe.

Well I did manage to work that one out but was not sure exactly what you meant by it but I think I’ve now managed to work it all out; it’s so much easier with a diagram/pics though.

So, you have a new extension with loo & the builder has vented this new loo into the existing stack which presumably serves an upstairs bathroom? If the drain invert serving the new loo is a maximum of 1.3m from the floor level (where the loo is mounted) Building Regs (Part H, page 7 diagram 1) allows direct connection of a ground floor W/C, providing the drain system has additional means of open ventilation. Your existing stack would appear to provide this so I don’t really see why the builder has deemed it necessary to introduced a vent to the new loo & high level inspection chamber install. I can’t see there being a problem with the original loo drawing the trap on the new loo if it’s on an open stack. Did your builder actually test to see if there were any problems or is he just playing it safe? I assume you’ve had an LABC inspection, did the Building Inspector deem additional venting was necessary? If you’ve had no inspection, you should have done as it’s a new connection which is notifyable work; as is the extension itself. Have you asked your builder why he did it?

 

[BuildingNovice]

Richard,

Thanks again for your reponse.

>>So, you have a new extension with loo & the builder has vented this new loo into the existing stack which presumably serves an upstairs bathroom? <<

Yes, the existing stack serves an upstairs bathroom.

The new wc is vented but only indirectly (connects to inspection chamber, which connects to deeper brick chamber, which connects to main house soil stack which is vented to air) - does that count?

>>If the drain invert serving the new loo is a maximum of 1.3m from the floor level (where the loo is mounted) Building Regs (Part H, page 7 diagram 1) allows direct connection of a ground floor W/C, providing the drain system has additional means of open ventilation.<<

Does the inspection chamber count as the 'drain' for calculating the invert? Or is it the connected lower older brick chamber, which is about 2m below?

Do you know why the 1.3m rule exists? Is it that longer distances would pull the trap (building up more of a vaccum)?

>>Your existing stack would appear to provide this so I don’t really see why the builder has deemed it necessary to introduced a vent to the new loo & high level inspection chamber install.<<

Does it counted as being venitlated when this is indirect through another chamber?

>> I can’t see there being a problem with the original loo drawing the trap on the new loo if it’s on an open stack.<<

I'm not so worried about house bathroom wc drawing new wc trap, but given a straight vertical soil pipe under new wc (although only a short 1.2 metre vertical drop) am worried that drop may pull the trap.

>>Did your builder actually test to see if there were any problems or is he just playing it safe? I assume you’ve had an LABC inspection, did the Building Inspector deem additional venting was necessary? If you’ve had no inspection, you should have done as it’s a new connection which is notifyable work; as is the extension itself. Have you asked your builder why he did it?<<

I've asked builder and am awaiting a response; just want to be sure about the concepts before I chat to him, as I am not a professional (just a householder). We do have a building control chap, but have left builder to deal with him direct.

 

[BuildingNovice]

Builder says he has put the 'soil vent pipe in to allow air into drains'.

I will try and clarify with him but why would you need to allow air in to the drains? I can undersand wanting to get build up gases out.

 

[Richard C]

sorry m8 going off line now so will have a more detailed look tommorow.

 

[Richard C]

The new wc is vented but only indirectly (connects to inspection chamber, which connects to deeper brick chamber, which connects to main house soil stack which is vented to air) - does that count?

Unless I’ve misunderstood, yes; I would not have expected any problems as it’s connected to a vented foul drain.

Does the inspection chamber count as the 'drain' for calculating the invert? Or is it the connected lower older brick chamber, which is about 2m below?

The distance is measured from the floor to the bend;
http://www.planningportal.gov.uk/uploads/br/BR_PDF_ADH_2002.pdf
see page 7 diagram 1; the distance to the inspection chamber is not relevant.

Do you know why the 1.3m rule exists? Is it that longer distances would pull the trap (building up more of a vaccum)? Does it counted as being venitlated when this is indirect through another chamber?

An unvented loo with an invert deeper than that would risk pulling the trap of the loo connected to it. It’s the vertical height the water falls through that matters as it invariably falls as a solid column; at that point no air can get behind it, a bit like putting your finger over the end of a bike pump & pulling the plunger out sucks on your finger. Once the water it hits the invert, gravity takes over, the water starts to flow out & as long as the foul drain is ventilated from another stack, air will flow back over the top of the water venting the loo.

I'm not so worried about house bathroom wc drawing new wc trap, but given a straight vertical soil pipe under new wc (although only a short 1.2 metre vertical drop) am worried that drop may pull the trap.

As above; you won’t draw the bathroom w/c trap if it’s on an open vented soil stack.

I've asked builder and am awaiting a response; just want to be sure about the concepts before I chat to him, as I am not a professional (just a householder). We do have a building control chap, but have left builder to deal with him direct.

Your BI should have been invited to inspect the connection before it was backfilled & they sometimes require to witness testing. Be careful as the onus to comply with BR’s & get it signed off as compliant is on you & not your builder; he has no real obligation to deal with inspections unless he has signed a contract saying he will do so.

Builder says he has put the 'soil vent pipe in to allow air into drains'.
I will try and clarify with him but why would you need to allow air in to the drains? I can undersand wanting to get build up gases out.

All foul drains must be ventilated to take account of negative pressure; you must allow air into the drain system when you flush or run water or you risk continually pulling water from the traps, leading to smells. You already have ventilation into the drain system by virtue of the original open soil stack; this will vent the lower inspection chamber which should also vent the new upper inspection chamber & the new loo unless there is some form of sump.

You must also allow positive ventilation to prevent a build up of pressure due to toxic gasses (methane); hence AAAV’s (Durgo valves) can only be fitted to a foul drain that has another open stack elsewhere.

 

[BuildingNovice]

You've been very helpful, thank you

I've managed to attach a drawing!

View media item 23509
>>I would not have expected any problems as it’s connected to a vented foul drain<<

So we should not need any pipe for venting gases out of inspection chamber

>>The distance is measured from the floor to the bend;
; the distance to the inspection chamber is not relevant. <<

The pipe from WC to inspection chamber does turn 90 degrees - so I would have thought the waste will have lost it's momentum at that point, so as WC to inspection chamber is less than 1.3m we should be OK and trap should not pull?

From points above it seems we don't need a pipe for venting gases out of inspection chamber nor for letting air in (as WC trap should not be pulled). I therefore cannot think why the vent pipe has been installed, but am better equipped to discuss with builder.

 

[Richard C]

I can see now why he’s done it but unless the new access chamber is fitted with an air tight cover, any positive build up of gasses will vent naturally through the labyrinth on the inspection cover. It looks like a bit of a “not sure after thought” to me & I think you need to ask your builder why he’s done it; he may of course know something you don’t! I would also seek guidance from your BI as to weather he thinks it necessary; it’s him you will ultimately have to satisfy. If he decides positive venting is required, an AAAV won’t help & the best alternative might be to fit a new vertical & separate full height open stack from where it currently kicks left to the existing stack. It will at least look better than that & a 5m length of black 110mm soil pipe, some clips & a bird cover wont cost much.

 

[BuildingNovice]

>>I can see now why he’s done it <<

Sorry if I'm a bit thick - why do you think he has done it?

>>unless the new access chamber is fitted with an air tight cover<<

The new inspection chamber cover does not seem to be airtight.

>>the best alternative might be to fit a new vertical & separate full height open stack from where it currently kicks left to the existing stack. It will at least look better than that & a 5m length of black 110mm soil pipe, some clips & a bird cover wont cost much.<<

To get to left of existing stack, presumably he can lay pipe underground (from inspection chamber) i.e. horizonal run still allows proper venting?

Can he connect vent pipe from inspection chamber directly to main soil pipe, and do this underground so you can't see it at all?

 

[Richard C]

Sorry if I'm a bit thick - why do you think he has done it?

As you’ve already said in your last post, I think he believes (or has been told) the new top chamber needs positive venting.

The new inspection chamber cover does not seem to be airtight.

Exactly as I said; you need to get a view from your LABC, they are the ones who will be signing it off.

To get to left of existing stack, presumably he can lay pipe underground (from inspection chamber) i.e. horizonal run still allows proper venting?

Why does he need to do that? He can either vent from the pipe he’s already laid straight up the wall or tee into the new invert on the outside & run a new vent stack straight up from there; as it's just for venting, it can even be a smaller diameter pipe.

Can he connect vent pipe from inspection chamber directly to main soil pipe, and do this underground so you can't see it at all?

I don’t see how that helps as it won’t provide any more positive venting that what you currently have. I obviously haven’t seen it but I don’t really understand why didn’t he just dig down & run the invert straight into the side of the existing brick drain unless I’m missing a trick; sketch doesn’t really show levels that well, perhaps posting a few photos of the chambers & pipe runs would make things clearer.

 

[BuildingNovice]

>>Why does he need to do that? He can either vent from the pipe he’s already laid straight up the wall or tee into the new invert on the outside & run a new vent stack straight up from there<<

I'm just thinking of a way to reposition the new vent pipe (assuming it's needed and can't be eliminated), as it is quite ugly as it stands.

If when you refer to 'teeing into the new invert on the outside' you are referring to the invert of the pipe connecting new WC to inspection chamber then we could tee in but instead of going straight up (which is what it effectively does now), we could go horizontally underground to connect to main stack - that way we eliminate new vent pipe but keep new chamber vented, and end up with only one vent pipe.

Sorry if I am not fully understanding what you are saying.

 

[Richard C]

I'm just thinking of a way to reposition the new vent pipe (assuming it's needed and can't be eliminated), as it is quite ugly as it stands.

If you’ve a need to ventilate the drain you’re stuck with it!

If when you refer to 'teeing into the new invert on the outside' you are referring to the invert of the pipe connecting new WC to inspection chamber then we could tee in but instead of going straight up (which is what it effectively does now), we could go horizontally underground to connect to main stack - that way we eliminate new vent pipe but keep new chamber vented, and end up with only one vent pipe.

You may be able to do that but I can’t see exactly what’s been done over the internet & from the iffy sketch you’ve provided. We seem to be going around in circles as I’ve expressed my opinion on why your builder has done what he has (which I agree isn't good) & suggested several alternatives but so far none seem to be acceptable to you; why don’t you just talk to your builder & take advice from your LABC; no matter what I or he says, it’s your BI who ultimately needs to be satisfied & going to approve your extension.

I’m sorry but I'm not going to dedicate any more of my time to this unless you provide some decent details & photographs of what’s involved; alternatively you can do your own research & come back with definitive questions which I will do my best to answer.

 

[BuildingNovice]

Many thanks Richard, and for your patience explaining to a novice!

I will be speaking to my builder shortly, and the BI if necessary - I just wanted to understand the issues before I do (otherwise they can bamboozle me with science!), and you've done a good job of improving my understanding. Much appreciated.