Air admittance valve / soil vent pipe

[Temp]

7 hours ago, Robin Banks said:

The soil pipes for the ensuite and WC aren't tied into the existing stack either since that's upstairs on the other side of the house.

 

Is that existing stack open vented?

[Temp]

6 hours ago, Robin Banks said:

I can see where the toilet soil pipes disappear into the poured concrete floor and there's no sign of anything that looks like an AAV. Am I right in thinking that any AAV would need to be at least at the height of the sink overflow ?

 

Yes. Typically it would be on the top of a short stub stack. At about chest height.

 

 

[Robin Banks]

Couldn't get any photos because it's so cramped. But, I have drawn a picture of what's there. No sign of anything resembling an AAV

[Robin Banks]

3 hours ago, Temp said:

 

Is that existing stack open vented?

Yes, the toilet in the old part of the house is attached to a classic cast iron open vented stack. But that whole thing isn't tied into the extension at all, it lives by itself on the other side of the house.

[PeterW]

1 hour ago, Robin Banks said:

Yes, the toilet in the old part of the house is attached to a classic cast iron open vented stack. But that whole thing isn't tied into the extension at all, it lives by itself on the other side of the house.

 

That’s fine then - it’s venting the sewer. You may get some sink gurgling when a toilet in the extension is flushed but otherwise that is to regs. If it’s a problem then fit a couple of 32 or 40mm AAVs or anti siphon wastes to the basins. 

[Robin Banks]

I guess the thing I'm having difficulty getting my head around (as a newbie to all this) is how the vented stack in the house can prevent sewer gas potentially entering the extension when a toilet in the extension is flushed ? It can't can it ?

 

Would it not have been better for the builder to follow the architect's plans and put a SVP in the extension, or - failing that - have AAVs on the toilets ? I mean, better to have them and not need them than need them and not have them, right ?

[Carrerahill]

14 minutes ago, Robin Banks said:

I guess the thing I'm having difficulty getting my head around (as a newbie to all this) is how the vented stack in the house can prevent sewer gas potentially entering the extension when a toilet in the extension is flushed ? It can't can it ?

 

Would it not have been better for the builder to follow the architect's plans and put a SVP in the extension, or - failing that - have AAVs on the toilets ? I mean, better to have them and not need them than need them and not have them, right ?

If the stack is internal then you must fit an AAV on top, the AAV only opens, assuming the diaphragm is working properly, when there is suction on the stack, it's the suction which opens the AAV, so if the pipe is in vacuum then nothing can be coming out of it.

[Robin Banks]

That's a good explanation, thanks. But there are no AAVs or SVP in the extension, that's the thing I have a problem with. PeterW explained that the old stack in the house (which has an SVP) is enough, but I just don't understand why since it can't prevent sewer gas from (potentially) getting into the extension. At least, I don't think it can.

[PeterW]

37 minutes ago, Robin Banks said:

That's a good explanation, thanks. But there are no AAVs or SVP in the extension, that's the thing I have a problem with. PeterW explained that the old stack in the house (which has an SVP) is enough, but I just don't understand why since it can't prevent sewer gas from (potentially) getting into the extension. At least, I don't think it can.

 

Sewer gas is a very old concept and much less common these days. AAV/SVP are normally about stopping suction of water traps in WCs, showers and basins and the associated 'gurgling' you get as air is drawn through the water traps. These can be simply fixed by either using an inline AAV on a waste under a sink, or an AAV trap.

 

 

[Ed Davies]

23 minutes ago, PeterW said:

Sewer gas is a very old concept and much less common these days. AAV/SVP are normally about stopping suction of water traps in…

 

Aren't these two separate issues? My understanding is that somewhere in the system you need a vent pipe to stop gasses building up in the pipe work, i.e., higher pressure in the pipes so smelly gas pushes past the traps and gets out into the rooms but, separately, each vertical run of pipe needs somewhere near or at the top for air to get in to prevent suction behind a large blob of liquid/solid falling down the pipe, acting as a piston, resulting in low enough pressure that air from the room gurgles past the traps which is an irritating noise and, worse, can empty the trap.

 

What I find odd is that SVPs are usually big (110mm?) despite their having to only vent a very slow evolution of gas whereas AAVs which could need to let quite a lot of air into the system in a few seconds are quite small. It seems to me that big SVPs are likely only a result of tradition from the days when the two functions were combined in a single vent pipe which both vented gas and allowed air in to prevent suction. Maybe also from when toilets used a larger quantity of water at each flush.

[Temp]

As I recall on a new housing estate not every house needs to have an open vented stack to dissipate sewer gas. I've seen guidance that says only thing one in four must have one.

 

I think most houses have one to prevent water being dragged out of traps as others have said. But even this isn't always a problem. It's common to find downstairs WC just go straight into the floor with no stack.

 

@Robin Banks Do you have a mini stack like the diagram posted above? If so is the top capped off?

 

 

 

 

 

[Temp]

11 hours ago, Ed Davies said:

What I find odd is that SVPs are usually big (110mm?)

 

That's just because the pipe used for a WC is 110mm. Its easier to fit a 110mm AAV to the top of the stub stack than to fit a reducer and smaller AAV.

[Ed Davies]

7 hours ago, Temp said:

That's just because the pipe used for a WC is 110mm. Its easier to fit a 110mm AAV to the top of the stub stack than to fit a reducer and smaller AAV.

 

Right, but back the “olden days” when people didn't have AAVs [¹] but just an SVP going up the outside of the house it would still have been cheaper and less unsightly to put a reducer above the highest connection (bathroom typically) then, say, 50mm up to somewhere above roof level.

 

[¹] I.e., a significant proportion of existing UK housing.

Edited September 26, 2019 by Ed Davies

[joe90]

4 minutes ago, Ed Davies said:

Right, but back the “olden days” when people didn't have AAVs [¹] but just an SVP going up the outside of the house it would still have been cheaper and less unsightly to put a reducer above the highest connection (bathroom typically) then, say, 50mm up to somewhere above roof level.

 

I did just this, didn’t need an AAV as a soil pipe externally on the garage was sufficient but to stop any “gurgling” and possible problems at the end of the 110mm pipe run to bathrooms I reduced it to 50mm and ran it up the corner of the airing cupboard, simples .

[Ed Davies]

23 minutes ago, joe90 said:

I reduced it to 50mm and ran it up the corner of the airing cupboard, simples .

 

Where does it go from there? What's on the end of the pipe?

[Carrerahill]

22 hours ago, Robin Banks said:

That's a good explanation, thanks. But there are no AAVs or SVP in the extension, that's the thing I have a problem with. PeterW explained that the old stack in the house (which has an SVP) is enough, but I just don't understand why since it can't prevent sewer gas from (potentially) getting into the extension. At least, I don't think it can.

Do you have an open end in the extension or does it just take a 90 or whatever into the pan connection and thus it is sealed? If so then there is nowhere for gas to escape, if you have an open end soil pipe then this must be addressed. Mainly just for smell issues.

Edited September 26, 2019 by Carrerahill

[joe90]

38 minutes ago, Ed Davies said:

 

Where does it go from there? What's on the end of the pipe?

 

Sorry forgot to say 50mm AAV on the pipe just below the ceiling, above all water levels and accessible for maintenance.

[Ed Davies]

43 minutes ago, joe90 said:

Sorry forgot to say 50mm AAV on the pipe just below the ceiling, above all water levels and accessible for maintenance.

 

Ah, I'd have assumed that except for your previous comment:

 

1 hour ago, joe90 said:

…didn’t need an AAV as a soil pipe externally on the garage was sufficient…

 

But, yes, good to have confirmed that 50mm pipe to the AAV is sufficient. I also suspect that a 50mm (or even smaller) vent pipe would be sufficient.

 

My plan is

 

1) thin pipe venting the system by the treatment plant to get rid of any build-up of gasses (rainwater pipe?) and

 

2) and 50mm pipe from the nexus of pipes behind the bathroom up into the loft with an AAV there to prevent suction problems.

[joe90]

Sorry @Ed Davies for the confusion, I did not need an AAV (because of the stack on the garage at the farthest point from the plant) but installed one in the house anyway as I hate gurgling traps and it was so simple to instal. I read somewhere that reducing to 50mm was acceptable for an AAV (can’t remember where) but I am sure 40mm would do just to allow for air ingress. I am not convinced anti siphon traps work.

[Robin Banks]

On 26/09/2019 at 01:06, Temp said:

Do you have a mini stack like the diagram posted above? If so is the top capped off?

Nope - both the WC and ensuite are like my bad drawing - i.e. sink waste goes into pan connector behind WC and then that disappears into the ground.

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Edited October 3, 2019 by Robin Banks

[Robin Banks]

Thanks for all the useful posts.

 

In case anyone has a similar issue in the future, I contacted Building Control and asked they to clarify the position with respect to the building regs. They said that if there was a SVP on the architect's drawings, they would have expected that to be fitted. Failing that they would have expected there to be at least an air admittance valve in the boxing to the back of each toilet, as given the drainage layout that would be a requirement. If there was no space for standard size air admittance valves, smaller ones (50mm) could be used.

[Oz07]

Hijacking here. @joe90 you sure 50mm aav ok to stop a loo pulling traps? @Nickfromwales almost implies different saying can fit 2no. 50mm

[joe90]

12 minutes ago, Oz07 said:

Hijacking here. @joe90 you sure 50mm aav ok to stop a loo pulling traps? @Nickfromwales almost implies different saying can fit 2no. 50mm

I think so, if I remember correctly ?, a loo flushing does not fill the 110mm pipe completely! If a bath is emptied the waste pipe is full but it will be 50mm max. My AAV is 50mm and I have had no probs in the last two years. Saying that, if I had room to extend the waste in 110mm pipe and use a full size AAV I would. My BC chap saw it and  said nothing.

Edited January 15, 2020 by joe90

[CC45]

On ‎15‎/‎01‎/‎2020 at 20:17, Oz07 said:

Hijacking here. @joe90 you sure 50mm aav ok to stop a loo pulling traps? @Nickfromwales almost implies different saying can fit 2no. 50mm

I've fitted 2 x 50mm, heck of a lot simpler now than in a few month time.

[yebaws]

Interested to learn that you don't need an open vent in the house. Is there any restriction on how far away from the house the vent can be? We have a septic tank. Waste water enters tank from an inspection chamber and the fall pipe into the tank is vented. Would this count as the open vent for the system so far as building regs are concerned. Tank is maybe 13m away from closest outlet from house