External Air Admittance Valve ?

[JohnW2]

Hi folks.

Whilst Part H of the Building Regs has absolutely nothing to say about such matters, 1.33 of Approved Doc H says (in relation to AAVs on soil stacks)

"... Air admittance valves should not be used outside buildings or in dust laden atmospheeres.... "

Many people will no doubt say that is 'a regulation', although it clearly is not. On the other hand, FloPlast say in their documentation, regarding their AX110 product:

"Document H Clause 1.31 states that “Ventilating pipes open to outside air should finish at least 900mm above any opening into the building within 3 metres”. This new development by FloPlast, of an External Air Admittance Valve, will allow the installation of an external soil pipe within 3 metres of any opening and terminate at the same height as if it were installed internally, ie. 200mm (minimum) above the highest wet entry point to the soil vent pipe. See diagram below."

Are FloPlast telling the truth, or are there any other (real!) rules/regulations which would prevent the practice. If it is acceptable, it would save me a very long run of vent pipe, with a very complicated route that would present some access difficulties.

Kind Regards, John

 

[denso13]

If it is acceptable, it would save me a very long run of vent pipe

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

 

[JohnW2]

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

Thanks. That's obviously what I was hoping to hear!

As I said, I don't doubt that there will be some who will say that it is "not allowed", because of what Approved Doc P says! Is that document just "out of date", or what? In fact, I wonder why the statement was ever there - did the AAVs of old perhaps not function satisfactorily if they got wet, or something like that?

It sounds as if there is no longer any particular reason to have long vent pipes on outside stacks?

Kind Regards, John

 

[denso13]

I wonder why the statement was ever there - did the AAVs of old perhaps not function satisfactorily if they got wet, or something like that?

I think it was to do with wet/freezing temps causing the valves to stick and not work. Floplast claim their design avoids that issue, IIRC.

Are you involving the LA building control? If so, just check, if not, then crack on.

 

[JohnW2]

I think it was to do with wet/freezing temps causing the valves to stick and not work. Floplast claim their design avoids that issue, IIRC.

Yes, I can imagine that might well have been the reason, and I suppose that we just have to trust FloPlast to have found a way of avoiding it. On the face of it, that would seem a difficult task - the 'outlet' of the valve must be exposed to air, so one can't avoid it also being exposed to wet - and the 'wet' will freeze if its could enough!

Are you involving the LA building control? If so, just check, if not, then crack on.

I'm currently thinking about the future. I've got to remove most of the (probably 100+ years old) cast iron vent pipe soon, because it's falling apart in places and hence getting quite dangerous (some is pretty high up), and I'll put a FloPlast AAV on it at least as a temporary measure (the pipe below the highest branch still seems fine).

As we often discus in the Electrics forum, the danger of 'asking LABC' is that might get the answer one doesn't want to hear! Individual BCOs are no more likely to have expert knowledge of drainage than of electrics, so the safest route for them is to regard the Approved Documenet as being gospel!

Kind Regards, John

 

[denso13]

As we often discus in the Electrics forum, the danger of 'asking LABC' is that might get the answer one doesn't want to hear!

Yes, I would run using the external AAV past them, but only if you are using them anyway. Just in case they a different view, however daft it is.

If not, then no issues with it.

Floplast claim "Tested and approved for use in installations varying between -20° & +60°c (no insulation required)", which may make them suitable for external use.

 

[JohnW2]

Yes, I would run using the external AAV past them, but only if you are using them anyway. Just in case they a different view, however daft it is. If not, then no issues with it.

Agreed.

Floplast claim "Tested and approved for use in installations varying between -20° & +60°c (no insulation required)", which may make them suitable for external use.

Yes, they say that. However, I still wonder how they prevent water getting to the 'outlet (which, by definition, has to be 'exposed') and then freezing, thereby blocking/jamming the valve. However, that's not my problem - I can 'hide behind' their claims and assertions that it's OK for external use

Kind Regards, John

 

[Hugh Jaleak]

It sounds as if there is no longer any particular reason to have long vent pipes on outside stacks?

Drains still need to be vented to allow positive pressure out, AAV's have their place, but are not a substitute for a vented stack.

As explained above, there was an issue with AAV's freezing in cold weather, hence they were unable to operate as intended, which gave rise to issues with the system, hence why the regs said they had to be installed internally. Now this has been overcome with external grade AAV's the Regs really need updating to reflect that.

 

[JohnW2]

Drains still need to be vented to allow positive pressure out, AAV's have their place, but are not a substitute for a vented stack.

An 'open' vented stack is obviously pretty foolproof (as well as being the traditional approach), but it sounds as if there might now be an acceptable alternative.

As explained above, there was an issue with AAV's freezing in cold weather, hence they were unable to operate as intended, which gave rise to issues with the system, hence why the regs said they had to be installed internally. Now this has been overcome with external grade AAV's the Regs really need updating to reflect that.

You seem to be almost contradicting yourself here, by implying that the "external grade AAVs" which have appeared are "a substitute for a vented stack".

Unless there are other "Regs" of which I am unaware, there has never been a regulator prohibition of external AAVs, but I agree that, if the external grade AAVs are now acceptable, then the guidance in Approved Document H (which I don't think has been revised since 2015) ought to be updated to reflect that. Otherwise some people (possibly including some BCOs) are likely to continue to insist (incorrectly) that "the regs forbid external AAVs)!

Kind Regards, John

 

[Hugh Jaleak]

An 'open' vented stack is obviously pretty foolproof (as well as being the traditional approach), but it sounds as if there might now be an acceptable alternative

No, it's pretty simple, an open vent allows air movement in and out of the system, an AAV does exactly as it says on the tin, it only admits air. Regs still state an open vent must be fitted at the highest point of the drainage system. To completely seal the system with AAV's will not end well. Refer to Part H, section 1.33.

You seem to be almost contradicting yourself here, by implying that the "external grade AAVs" which have appeared are "a substitute for a vented stack".

No, where did I say that? There are times when an AAV could be used instead of an open vent, e.g. on an en suite, provided the main bathroom stack is vented or vice versa. If it was found preferable to fit both stacks externally, then an external grade AAV could be used on one if required. This wouldn't have been possible previously, the soil stack would have either needed to be vented, or fitted internally.

Unless there are other "Regs" of which I am unaware, there has never been a regulator prohibition of external AAVs

Part H, Section 1.33, " Air admittance valves should not be used outside buildings"

 

[JohnW2]

No, it's pretty simple, an open vent allows air movement in and out of the system, an AAV does exactly as it says on the tin, it only admits air.

That's obvious. However, as far as I am aware, there is no functional need for air to be 'let out' - that is just an unwanted side-effect of having an open vent (there to allow air in) - and is the reason why the guidance is that such an open vent should be high enough for 'let out' air to not get into the property.

Regs still state an open vent must be fitted at the highest point of the drainage system. To completely seal the system with AAV's will not end well. Refer to Part H, section 1.33.

As I said, I am aware of no such regulation. See comments below about the guidance in 1.33 of Approved Document H.

No, where did I say that?

You started by writing:

.... AAV's have their place, but are not a substitute for a vented stack.

... and then went on to write:

...... Now this has been overcome with external grade AAV's the Regs really need updating to reflect that.

If you believed that AAVs could not "be a substitute for a vented stack", why would you suggest that the guidance (which you call "Regs") should be updated to acknowledge the acceptability of 'external grade AAVs'?

There are times when an AAV could be used instead of an open vent, e.g. on an en suite, provided the main bathroom stack is vented or vice versa. If it was found preferable to fit both stacks externally, then an external grade AAV could be used on one if required. This wouldn't have been possible previously, the soil stack would have either needed to be vented, or fitted internally.

You are again talking of the days before appearance of 'exterior grade AAVs' - and, in any event, as I keep saying, there was actually (to the best of my knowledge) no regulation preventing external use of an AAV even "previously" (previous to the appearance of the new product(s).

Part H, Section 1.33, " Air admittance valves should not be used outside buildings"

That quote, which I included at the very start of my first message when I started this thread, is from Approved Document H, not from Part H (of the Building Regulations) and, as such, is merely guidance - not 'a regulation' or 'requirement. In fact, the only relevant thing which Part H ('the law', 'regulations', 'requirements') says about drainage is that there should be adequate provision for disposal of foul water, with absolutely nothing about details of how that is achieved.

However, given the apparent contradiction in your statements, I would be interested to know whether you feel that, now, there is ever any need to have an open (external) vent rather than an 'external grade AAV' (installed externally) - and, if so, why?

Kind Regards, John

 

[Hugh Jaleak]

You are quoting parts of what I said, not the whole sentence.

hence why the regs said they had to be installed internally. Now this has been overcome with external grade AAV's the Regs really need updating to reflect that.

Now external grade AAV's are available, they can be fitted externally. Simple. However, there are still occasions when an open vent is required.

However, as far as I am aware, there is no functional need for air to be 'let out'

Then I am afraid you have no idea about drains, ventilation and hydraulics.

AAV's as I said previously, have their place. If the main bathroom in a property connects to the head of the drain, then a vented stack is required. An en Suite elsewhere in the property, connecting lower down the drain run would be ok with an AAV on the stack, which could allow for easier installation/siting of the stack with reference to an openable window or any other portal into the property through which, foul air could ingress.

Part H is the Approved Documents, a Building Inspector would expect to see the work carried out to comply with these, if they were not happy, then they could refuse to sign the work off. Poor practice on New Builds is now endemic, Drainage Companies are kept in business sorting out cocks ups through blocked and poorly functioning drains, simple because little or no care has been taken in their installation, and/or they've been allowed to fill up with debris as work has gone on on site.

 

[JohnW2]

Now external grade AAV's are available, they can be fitted externally. Simple.

OK, so that seems to indicate that you agree that they are (now) "a substitute for a ventilated stack"? But you then go on to say ...

However, there are still occasions when an open vent is required.

Can you educate me as to what are those occasions. and why they require an open vent?

Then I am afraid you have no idea about drains, ventilation and hydraulics.

I have plenty of 'ideas' about those subjects, but perhaps you could help me understand what aspects of them mean that there is a functional need for a stack to be able to 'let air out'?

AAV's as I said previously, have their place. If the main bathroom in a property connects to the head of the drain, then a vented stack is required. An en Suite elsewhere in the property, connecting lower down the drain run would be ok with an AAV on the stack, which could allow for easier installation/siting of the stack with reference to an openable window or any other portal into the property through which, foul air could ingress.

Yes, you said all that before, but you haven't yet helped me to understand why you feel that an external AAV is not suitable/acceptable when "the main bathroom connects to the head of the drain".

Part H is the Approved Documents, a Building Inspector would expect to see the work carried out to comply with these, if they were not happy, then they could refuse to sign the work off.

I'm sure some BCOs would, but that doesn't make it correct behaviour on their part. We see exactly the same sort of problems with BCOs and Part P of the regs. If they refuse to sign off work, they should be challenged to indicate which requirement of the relevant Part of the Building Regs (Part H in the case we are discussing) has not been complied with.

In any event, I'm still not clear about your view, so would appreciate clarification. Do you believe that a BCO could/would (legitimately) refuse to 'sign off' work which included an 'exterior grade AAV' installed externally on a stack fed from the 'main bathroom'?

Kind Regards, John

 

[Hugh Jaleak]

Can you educate me as to what are those occasions. and why they require an open vent?

I have plenty of 'ideas' about those subjects, but perhaps you could help me understand what aspects of them mean that there is a functional need for a stack to be able to 'let air out'?

Sewage, by it's nature consists of decomposing organic matter, and as such can create various gases as a result of this process, Methane and Hydrogen Sulfide are the 2 main concerns. Methane tends to be les of an issue, but Hydrogen Sulfide is nasty stuff. It is created by the breakdown of organic matter in the absence of oxygen, attacks both metal and concrete, and the level of exposure deemed safe is quite low, with concentrations of as little as 20ppm being injurious to health. Therefore, if a sewer system can be vented, this give a better chance of air movement through the system and help prevent gas build up.

Then we have the issue of 'Combined Sewers' where rainwater and foul are discharged in the same sewer. The Victorians went with this idea, for several reasons. Firstly it was an easy option, secondly, a good storm would wash the drainage system out for them, and thirdly, before modern methods of Sewage Treatment were developed, the town sewer outfall often just used to discharge onto land. When it rained heavily, the resulting flow gave the soil a good wash off, (usually I suspect rinsing the town effluent build up into the nearest watercourse....)

Given the increase in flow during such events, and many sewers running at capacity, the water will need to displace the air in the system, vents help achieve this. Otherwise WC pans and gullies everywhere would be bubbling up with trapped air looking for the easiest route of escape.

This situation often manifests on this forum, with Contributors asking why their WC fills right up when flushed, before slowly subsiding, often with a gurgling from another appliance. Simply put, usually there is a blockage in the drainage system, sealing downstream off, the AAV is sealing the system shut upstream, the discharge of waste from the WC needs to displace the equivalent volume of air from the system, so it looks for the easiest way out.

Yes, you said all that before, but you haven't yet helped me to understand why you feel that an external AAV is not suitable/acceptable when "the main bathroom connects to the head of the drain".

An external AAV is fine, provided there is an open vent elsewhere on the system, ideally at the head of the drain run. I was trying to illustrate an example, whereby a property has two Bathrooms with independent stacks. Provided one of these stacks is vented, the other may be terminated with an AAV.

In any event, I'm still not clear about your view, so would appreciate clarification. Do you believe that a BCO could/would (legitimately) refuse to 'sign off' work which included an 'exterior grade AAV' installed externally on a stack fed from the 'main bathroom'?

BCO's all have their own interpretation of the Regs, I have been on jobs where we've had 2 from the same office at the same Council come out, and what one had previously had no issue with, his colleague, covering for Holidays, was making a right fuss about! We had to carry out a lot of additional work to satisfy his demands. Once his Colleague returned from his Holidays, we went back to the previous method and not a word was said....

 

[JohnW2]

Sewage, by it's nature consists of decomposing organic matter, and as such can create various gases as a result of this process, Methane and Hydrogen Sulfide are the 2 main concerns. Methane tends to be les of an issue, but Hydrogen Sulfide is nasty stuff. It is created by the breakdown of organic matter in the absence of oxygen, attacks both metal and concrete, and the level of exposure deemed safe is quite low, with concentrations of as little as 20ppm being injurious to health.

All true.

Therefore, if a sewer system can be vented, this give a better chance of air movement through the system and help prevent gas build up.

'Gas build-up' in the sewer system?

Then we have the issue of 'Combined Sewers' where rainwater and foul are discharged in the same sewer....... When it rained heavily .... Given the increase in flow during such events, and many sewers running at capacity, the water will need to displace the air in the system, vents help achieve this. Otherwise WC pans and gullies everywhere would be bubbling up with trapped air looking for the easiest route of escape.

I'm not sure I get that one. If the sewers are "running at capacity" (which I presume means that the sewer pipes are more-or-less full of water), then that water will presumably already have pushed most of the air in the sewer system downstream, and the effect of a high rate of water flow through essentially full pipes should be to reduce the air pressure upstream (including in a property's drainage system), hence 'sucking' air into vent pipes, either through open vents or AAVs, shouldn't it?

Furthermore, as an additional factor, if for some reason the air pressure in the sewer system near the property were to rise (rather than fall), at least some of the air would presumably escape through the rainwater pipes ('bubbling up' through water traps were necessary), wouldn't it?

An external AAV is fine, provided there is an open vent elsewhere on the system, ideally at the head of the drain run. I was trying to illustrate an example, whereby a property has two Bathrooms with independent stacks. Provided one of these stacks is vented, the other may be terminated with an AAV.

Yes, I understand that to be your view. I just wonder how widespread it is.

BCO's all have their own interpretation of the Regs, I have been on jobs where we've had 2 from the same office at the same Council come out, and what one had previously had no issue with, his colleague, covering for Holidays, was making a right fuss about!

Yes, that definitely happens, but I don't think it should. I would say that any/all BCOs should accept ('sign off') any work which is compliant with the Building Regs (i.e. any work which does not violate any requirements of the Building Regs).

Kind Regards, John