External Air Admittance Valve ?

[JohnW2]

@denso13 ,at the very start of this thread, you responded to my question with what appeared to be a very simple and clear answer, when you wrote:

Yes, it's fine, I have a Floplast one outside.

I see that you have now 'Thanked' Hugh Jaleak for his posit in which he expressed the view that it is not acceptable to have an external AAV as the sole 'venting' of a single soil stack.

Does this mean that you agree with his view, and his reasoning behind it that he has presented?

Kind Regards, John

 

[denso13]

It was more on the need for a vent somewhere on the system, although I don't think it needs one per dwelling, just somewhere on the system. Sewer gases can be lethal and should be vented by an open stack somewhere, to stop dangerous levels occurring.

 

[JohnW2]

It was more on the need for a vent somewhere on the system, although I don't think it needs one per dwelling,

If I don't think too deeply, I can sort-of understand that view, but ....

just somewhere on the system. Sewer gases can be lethal and should be vented by an open stack somewhere, to stop dangerous levels occurring.

I presume that we all agree that escape of sewer gases into buildings must be avoided. However, unless there is a substantial blockage in the sewer system (which would obviously create other problems, and would need to be remedied), I struggle to see how the pressure of air within the waste pipework of an installation could rise to the extent that the gases could 'bubble back' through the water traps which are there to prevent ingress of gases into the building. Provided that there is at least some flow through the sewer, that should, if anything, tend to reduce (rather than increase) the upstream air/gas pressure - and, as above, if there in no flow through the sewer, then something obviously needs to be done about that!

What am I missing?

Returning to my practical issue, I'm obviously just talking about a single dwelling, so (bearing in mind your initial statement above),does it remain you view that it would be acceptable for me to have only an AAV (no open vent) for my particular dwelling (although someone will, I guess, ask "what if everyone did it?"!) ?

Kind Regards, John

 

[denso13]

would be acceptable for me to have only an AAV (no open vent) for my particular dwelling

Yes (probably).

 

[JohnW2]

Yes (probably).

Thanks again. That's probably the closest to a 'definite' answer I can probably hope to get- although I suspect that Hugh may well disagree with it.

As for the diagram you posted, what is this ...

?? .... and what is meant by this, and what is it pointing to:

?

... and, as a matter of interest, where does that diagram come from?

Kind Regards, John

 

[denso13]

... and, as a matter of interest, where does that diagram come from?

https://www.floplast.co.uk/uploads/related-documents/NafIzQZzuGZ7K3C7Zio7n3OEMSuv9k6eHxzoV7Ge.pdf

As for the diagram you posted, what is this ...

I think it just means there is more to the right but the diagram stops there.

? .... and what is meant by this, and what is it pointing to:

Perhaps just referring to the text to the left, i.e. numbers of non conventional stacks (AAVs) and what is required as the number of dwellings goes up. Not entirely clear.

 

[JohnW2]

https://www.floplast.co.uk/uploads/related-documents/NafIzQZzuGZ7K3C7Zio7n3OEMSuv9k6eHxzoV7Ge.pdf

Very interesting. Thanks.

The document does not seem to include any explanation of what (if any) additional design features are included in the AX110 ('external grade' AAV) to avoid freezing of water 'jamming' the valve. Indeed, the only difference from the ('internal') AF110 they mention is the absence of , the only difference from the ('internal') AF110 mentioned is the presence/absence of an "insect/debrs grille".

I think it just means there is more to the right but the diagram stops there.

Maybe!

.... Perhaps just referring to the text to the left, i.e. numbers of non conventional stacks (AAVs) and what is required as the number of dwellings goes up. Not entirely clear.

Possibly, but it looks as if the arrow may be pointing to the 'short' vertical pipe rising from the "up to 4th" dwelling from the right (presumably the most downstream end). It is a very badly drawn and annotated diagram!

So, without being sure what that 'unconventional stack' may be. the depicted line of 20 dwellings has only two conventional open vents - at the 10th and 20th dwellings from the most downstream end - is that correct? If so, where does that come from - is it based on some regulation, or is it something made up by FloPlast?

I can see one problem with this, that Hugh may well pick up on .... someone installing an AAV-only system in one dwelling, or a few adjacent dwellings, presumably cannot be certain that there is, and always will be, a conventional open vent within 10 dwellings?

Kind Regards, John

 

[denso13]

The document does not seem to include any explanation of what (if any) additional design features are included in the AX110 ('external grade' AAV) to avoid freezing of water 'jamming' the valve.

Not sure, they are tested in line with the appropriate BS and that is where the designation (A1 in this case) comes from.

at the 10th and 20th dwellings from the most downstream end - is that correct? If so, where does that come from - is it based on some regulation, or is it something made up by FloPlast?

Yes. I don't know where their info comes from, I've had a look at a few BS docs but nothing apparent. I'd hope it is based on ventilation requirements for drainage systems, but I'd be guessing. I'll do some more digging when I have time.

 

[JohnW2]

Not sure, they are tested in line with the appropriate BS and that is where the designation (A1 in this case) comes from.

Fair enough. Does that "A1" designation relate specifically to exterior use?

Yes. I don't know where their info comes from, I've had a look at a few BS docs but nothing apparent. I'd hope it is based on ventilation requirements for drainage systems, but I'd be guessing. I'll do some more digging when I have time.

Again, fair enough. I would imagine that it can't really be more than fairly rough guideline/rule-of-thumb, since no two groups of 10 or 20 dwellings (and their waste/sewer systems) are going to be totally identical.

I thought that I should perhaps explain/illustrate why I am so attracted by the possibility of using an external AAV. The present vent pipe, which is approaching 10 metres in total length, is anything but straight and vertical, and never could be. It has to get around two gutters, go across a small bit of flat roof and also go around a 'step' in that flat roof.

What I want to try to avoid, after removal of the present disintegrating cast iron, is replacing it, 'like-for-like (route-wise) with plastic - quite apart from all the the hassle (and access to some bits is not all that easy) it would cost a goodly amount in 'fittings'! The below is a rough diagram of the present situation, and it would obviously be a very attractive idea to be able to replace it all with just an external AAV (near the bottom of my diagram)!

Kind Regards, John

 

[denso13]

Fair enough. Does that "A1" designation relate specifically to exterior use?

No, suitable for freezing temps and installation below an appliance spill level, the external Floplast is an A1,

 

[denso13]

and it would obviously be a very attractive idea to be able to replace it all with just an external AAV (near the bottom of my diagram)!

Don't see why not, looks like a good solution.

 

[JohnW2]

No, suitable for freezing temps and installation below an appliance spill level, the external Floplast is an A1,

Thanks. That's what I really meant - maybe it doesn't explicitly say 'external', but suitable for use down to -20°C (presumably including when 'wet') is good enough for me!

Kind Regards, John

 

[JohnW2]

Don't see why not, looks like a good solution.

That's certainly my view - I imagine that you might agree that the alternative would be a bit of a nightmare (or, at least, 'unnecessary' work, time and cost)!

However, just for the hell of it, I'm probably going to try to ask the relevant LABC what their view/attitude would be (without revealing what property I am talking about!).

Kind Regards, John

 

[JohnW2]

The document does not seem to include any explanation of what (if any) additional design features are included in the AX110 ('external grade' AAV) to avoid freezing of water 'jamming' the valve.

Not sure, they are tested in line with the appropriate BS and that is where the designation (A1 in this case) comes from.

I've just noticed/realised - ALL of the FloPlast AAVs have an A1 rating, so that still leaves unanswered the question as to what is the difference in the AX110 that makes it 'uniquely' suitable for external use.

Any thoughts/ideas?

Kind Regards, John

 

[denso13]

so that still leaves unanswered the question as to what is the difference in the AX110 that makes it 'uniquely' suitable for external use.

A fly screen?

"1.4 AX110: The AX110 incorporates the same features as the AF110, with the exception of the inclusion of an insect/debris grill manufactured from Polypropylene.

Document H of the Building Regulations Clause 1.33 states that AAV’s should not be used externally or in dust laden atmospheres, however due to the design criteria requirements of the termination of SVP’s within 3 metres of an opening window, and the use of the roof as habitable space and also the upturn in loft/roof area conversions, and as a means of overcoming unsightly SVP installations, Building Control Officers are accepting their use.

FloPlast strongly advise that confirmation of acceptance of the use of the AX110 is gained from Building Control prior to installation."

https://www.floplast.co.uk/uploads/related-documents/NafIzQZzuGZ7K3C7Zio7n3OEMSuv9k6eHxzoV7Ge.pdf