A1 AAV

[Tristar]

Good morning, I am adding an en-suite adjacent to an existing bathroom. The soil stack is in the bedroom which will have the ensuite. To gain space I would like to use a class A1 AAV to remove the upper stack. The stack will have the 2 bathrooms and a downstairs cloakroom into it. One other property feeds into the inspection chamber outside.
Is this satisfactory regs wise?
If not, I would be grateful for helpful suggestions.

 

[Tristar]

Also, fitting the Durgo valve will make the job a lot easier when replacing the 3 branch with the 4 branch connector.

 

[Hugh Jaleak]

Head of the drain needs to be vented, replacing an open vent with an AAV is not a good idea and may open up another can of worms with possible odour issues if positive pressure cannot escape from the system.

If it helps, reduce the dry (vented section) to 3" (82mm) pipework, but I would advise against removing the vent altogether. Some find out the hard way when things go horribly wrong and a backdraft blows an unholy mess out the toilet.

 

[Tristar]

Thanks Hugh, I have another bathroom en-suite the other side of the house which connects via another stack to the sewer downstream of the aforementioned inspection chamber, and it has the kitchen and utility room connected also. This group have had a Durgo in the ensuite with no odour or other backflow problems for several years, hence my consideration of fitting one the other side of the house.
I am just a bit concerned because the adjacent house has a soil stack which exits into the shared chamber, and may mean I infringe the regulations.
Would it help if I add AAV’s to the shower and basin drains?

 

[frutbunn]

Providing the system serves no more than 4 dwellings a vent is not required.

 

[Tristar]

I am surprised. Are you saying four dwellings can exit into a sewer chamber with no soil vents whatsoever?

 

[Madrab]

It is always best practice and good design to vent the head of any soil run regardless, especially when it is shared. Not sure where the 4 dwelling limit is specc'd, don't remember seeing it in Doc H.

I see more and more drainage issues where open vents have been are changed to AAV's as more people remove stacks from the inside corners of their bathrooms or the stacks moved from externally to internally and then an AAV is sited into the loft.

 

[frutbunn]

It is always best practice and good design to vent the head of any soil run regardless, especially when it is shared. Not sure where the 4 dwelling limit is specc'd, don't remember seeing it in Doc H.

I see more and more drainage issues where open vents have been are changed to AAV's as more people remove stacks from the inside corners of their bathrooms or the stacks moved from externally to internally and then an AAV is sited into the loft.

There is no guidance for AAV's in the approved doc H so you have to refer to the Agrement Certificate.
I've looked at the Durgo cert and the one for Hunter's AAV and they both state the same.

 

[Madrab]

If only it worked like that all the time. I've come across all sorts of problems where people have used durgos to remove vented stacks, problems that have then impacted others on the shared drain, usually because they have done the same and don't use supplementary venting or discuss it with the others on the shared drain.

I find it doesn't always work the way they say it should in the docs written by the company themselves and would always stick to what's proven.

 

[frutbunn]

If only it worked like that all the time. I've come across all sorts of problems where people have used durgos to remove vented stacks, problems that have then impacted others on the shared drain, usually because they have done the same and don't use supplementary venting or discuss it with the others on the shared drain.

I find it doesn't always work the way they say it should in the docs written by the company themselves and would always stick to what's proven.

I can't say I've ever had a single report of any problems where they have been used correctly.

 

[Hugh Jaleak]

Having seen the aftermath of a bathroom that's been redecorated a nice shade of brown, after attempts to jet a sewer in the vicinity have caused a blowback, then you soon realise the importance and requirement for correct ventilation on sewers.

Also the first I've heard about this 'Four dwellings' rule. I would also say the Building Regs override anything the manufacturers may say, ultimately whilst they manufacture the components, (and have a vested interest in selling them), they can only offer typical examples of use, no 2 drainage systems are the same, and a certain amount of knowledge from the drainlayer is (or isn't is some cases) involved in installing a system that will work and not cause issues.

My property uses drains that were laid in 1896, in the 20 years I've been here, never an issue. New flats built nearby, (still not at 100% occupancy), have had at least 3 instances of a blocked fouls ewer spilling across the pavement outside in the last 12 months.

 

[frutbunn]

Having seen the aftermath of a bathroom that's been redecorated a nice shade of brown, after attempts to jet a sewer in the vicinity have caused a blowback, then you soon realise the importance and requirement for correct ventilation on sewers.

Also the first I've heard about this 'Four dwellings' rule. I would also say the Building Regs override anything the manufacturers may say, ultimately whilst they manufacture the components, (and have a vested interest in selling them), they can only offer typical examples of use, no 2 drainage systems are the same, and a certain amount of knowledge from the drainlayer is (or isn't is some cases) involved in installing a system that will work and not cause issues.

My property uses drains that were laid in 1896, in the 20 years I've been here, never an issue. New flats built nearby, (still not at 100% occupancy), have had at least 3 instances of a blocked fouls ewer spilling across the pavement outside in the last 12 months.

First of all the approved documents are not regulations, they are guidance showing methods of satisfying the Regs, other approaches may be used. For example, INDEPENDANT testing and certification, one such organisation is the British Board of Agrement (BBA). What I have stated is in accordance with the BBA certification, as a BCO i have no legal powers to prevent the use of AAV's if installed in accordance with the certification. As I already stated the approved doc makes no mention of AAV's.
As for your new building, I can't really offer any comment as you have not gone into any detail, although I very much doubt AAV's would have had anything to do with sewage spilling across the pavement.

 

[Hugh Jaleak]

Simple answer with the new build is poorly laid drains. How some of the work gets passed on some of these new buid, estates is absolutely beyond me, seems the rules of drainlaying just get thrown out the window, and its a case of getting from A to B with pipework the quickest way possible, even if that means running from one chamber to the next on a 1:1 fall.

Working for a Utility Company, we are finding more and more issues now when trying to carry out routine and emergency sewer cleaning work, with drainage alterations having been carried out in properties, open vented stacks having been removed, (and replaced with AAV's), whereby the pressure fluctuations in the system, caused by either the jetting operation or the surge when a blockage is 'popped' pulling traps, and in the worst case scenario, blowing WC's.

Part H section 1.33 gives guidance on ventilation, and states "Where there is no open ventilation on drainage systems, or through connected drains, then alternative arrangements to relieve positive pressures must be considered." I would always urge someone unfamiliar with drainage to err on the side of caution and not substantially change the operation of a system.

 

[frutbunn]

Simple answer with the new build is poorly laid drains

That is unfortunately the way of things, was the new build a private inspector?

open vented stacks having been removed, (and replaced with AAV's)

Again was this done without any reference to any guidance. Did the instances you refer to follow the guidance.

Where there is no open ventilation on drainage systems, or through connected drains, then alternative arrangements to relieve positive pressures must be considered.

That consideration are the likes of BBA certification, British Standards etc.
As I have already stated I have never had a report of any problems on any systems using AAV's to either myself or any of my colleagues and I've been inspecting drainage before AAV's were around, however these systems were subject to being checked and inspected at the time of construction, obviously any consequent changes may not have been subject to similar controls.

 

[Hugh Jaleak]

That is unfortunately the way of things, was the new build a private inspector?

Again was this done without any reference to any guidance. Did the instances you refer to follow the guidance.

New build, afraid I couldn't say, but given the complete lack of H&S during the build, and the poor standard of the finished build, (just from an external viewpoint), I would have said either Stevie Wonder has passed it, or they've paid someone. Things range from same section of sewer keeps blocking, to missing roof verge sections, gable covers, uPVC doors that wont stay shut, rainwater overshooting/missing the gutters, downpipes coming apart/falling off the wall, and whichever Muppet managed to design it so they had a BT Cabinet in the middle of one of the entrances to the parking area, (which has subsequently been blocked off...), needs to also go to Specsavers. Heaven only knows about the internal snagging lists....

I have not idea whether the alterations to these drainage systems followed any guidance, I only know we come along to jet the sewer, usually as planned maintenance where there is a known issue, (fat build up/poor gradient/root ingress/something else), to try and prevent future issues, having no previous history of issues, only to find on this occasion an irate Householder who's just had their bathroom redecorated.... Then have the reams of paperwork and reports to do to explain how/why it might have happened, and all the preventive measures that need to be put in place to prevent a repeat performance by the next crew who attend.

My point is, advising people that it's OK to remove an existing open vent and cap their soil pipe with an AAV, with no knowledge or sight of their system, is very unwise. It's DIY'ers and bodge artists, looking for easy solutions, and most with little or no knowledge, (or care) to how a drainage system operates, that are causing the issues, and usually only find out when some sort of pressure buildup has resulted in a rather unpleasant eruption from the drains in some way shape or form.