totally confused/soil/vent/aav/durgo. Drainage and wastage systems and plumbing help, advice and answers

[bells]

i have not been on this site for a while,not wishing to sound stupid,i'm confused regarding when and where you can use a AAV/DURGO etc.reading some of the posts with conflicting answers is confusing to say the least.some say can be used anywhere internally above highest appliance.then someone suggests you can only use if you have a soil pipe venting outside.am i right in thinking,that you cannot bring inside a vent/soil pipe and vent into the loft void,without an external additional vent???HOPE THIS MAKES SENSE... MANY THANKS.

[rosebery]

An AAV is there to alleviate negative pressure in the soil system thus preventing syphonage and to prevent escape of noxious gases into the building. It does nothing for you whatsoever in respect of a build-up of positive pressure in the system.

Indeed Part H is quite clear that alternative means of dealing with positive pressure must be provided if an AAV is used. To my mind that means at least one "open to atmosphere" vent. So where you have your original vent/soil stack open to atmosphee and you install a second toilet feeding into the original system it is quite permissable to have an AAV on that extension to the system.

You should consult your local BCO to get their view.

Cheers

[bells]

rosebery,Thanks for that... here is another scenario,I have a two up two down terraced property,with a ground floor bathroom extension built on.The vent/soil pipe runs up the rear elavation of the property and finishes above the gutter.Some time after the bathroom ext.,we decided to do away with the flat roof (bathroom)and extend the small porch at the back door.A pitched roof was constructed over the two,consequently creating a void which we thought could be used to house the vent pipe with the AAV on top.We then decided to create a bathroom on the first floor,which is directly behind the vent pipe.We then decided we could'nt get enough height in the roof space to fit the AAV (porch).We then figured to take the vent pipe through the wall into the bathroom and finish it off with the valve,and thats how we got to this point.At present we have the downstairs wc with the AAV fitted on the vent pipe in porch,and it works fine,so why do I need a vent outside,if I connect the upstairs wc.I don't understand why you need the AAV at all if you are venting outside anyway.I thought the purpose of the valve was to replace the admission of an outside gas (air) in this case. Maybe I'll take some tiles off the porch roof and stick the stack back up there!!, UGLY though?

[rosebery]

“Rosebery,Thanks for that...”

No problem.

“here is another scenario,I have a two up two down terraced property,with a ground floor bathroom extension built on.The vent/soil pipe runs up the rear elavation of the property and finishes above the gutter.”

That meets Building regulations requirements.


“Some time after the bathroom ext.,we decided to do away with the flat roof (bathroom)and extend the small porch at the back door.A pitched roof was constructed over the two,consequently creating a void which we thought could be used to house the vent pipe with the AAV on top.”

If you removed the dry part of the stack (ie the vent element) and just substituted an AAV without providing alternative means of alleviating positive pressure build-up then this would be in contravention of building regulations. It isn’t clear from this part of your post if it was just a thought to make the change or if you have actually done it.


“We then decided to create a bathroom on the first floor,which is directly behind the vent pipe. “We then decided we could'nt get enough height in the roof space to fit the AAV (porch).We then figured to take the vent pipe through the wall into the bathroom and finish it off with the valve,and thats how we got to this point.”

Yes I see but you then would be compounding contravention of the Building regs because you still don’t have means of alleviating positive pressure in the system. The correct way to do this would be to reinstate the stack (if you have removed the vent pipe from the down stairs bathroom) and branch into it for the new toilet waste.


“At present we have the downstairs wc with the AAV fitted on the vent pipe in porch,and it works fine,so why do I need a vent outside,”

Because the soil / vent system isn’t working according to building regs as I understand your description.


“if I connect the upstairs wc.I don't understand why you need the AAV at all if you are venting outside anyway.I thought the purpose of the valve was to replace the admission of an outside gas (air) in this case.

You are right – you don’t.


“Maybe I'll take some tiles off the porch roof and stick the stack back up there!!”,

I think that would be best and certainly what I would be suggesting you do if I were doing the work for you.


“UGLY though?”

Maybe but it isn’t there to be aesthetically unappealing – it’s there to do a job. LoL.


Cheers

[bells]

Thanks again roseberry... I'm sorry to keep going on about this,but you mentioned negative and positive pressure within the system.I quote from a well known manufacture of sanitary products... Air admittance valves are designed to allow air into the pipework under negative pressure,but will not allow air to come out under a positive pressure.Why would you need to add an aav if you already have an outside vent,which is what you are saying.Could you give me some examples of any installation where you would need to use an aav,many thanks.

[rosebery]

Sorry I see I was unclear. Imagine this scenario:

You have a fairly ordinary installation in your house with a single vent and soil stack. The 1st floor toilet, bath , shower and WHB wastes all feed into this stack. Foul water goes down, nasty niffs go up and the system is balanced from a pressure POV. There is no syphonage because negative pressure doesn't build up. Positive pressure doesn't build up either because gases can escape.

Now consider that you want to add an en-suite say about 15 feet away from the existing stack on the first floor. This needs a fall, obviously, to work properly. If you just run all the wastes into the branch with no means then when the toilet is flushed negative pressure will drag water out of the basin etc traps thus breaking the seals and smells result because there is no vent to atmosphere. Actually syphonage can also happen with a bath syphoning water out of a basin or shower trap. In this case its quite permissible to fit an AAV at the top of the branch to admit air when the toilet is flushed and avoid syphonage. Overall the air pressures internally remain balanced because ther remains an open vent on the original stack.

Have I explained myself a little better this time?

Cheers

[bells]

Thanks again rosebery... going back to original post,the soil/vent pipe was seperated at about 9ft and a aav was fitted which works fine,because the ground floor now obsolete bath and w/basin discharged into a outside gulley.The w/c is still in use.Is it the distance from the stack thats causing the problem,your example (15ft)???.The proposed 1st floor bathroom backs onto the soil stack. I hope this is the last post. CHEERS!!

[rosebery]

The problem is that from your description it doesn't meet building regulations whether or not the AAV works physically because your system no longer has a vent at all unless you have one somewhere else that you haven't told us about. Or have I misunderstood you?

What I tried to do in my example was show the circumstances where an AAV can be fitted to avoid syphonage and nasty niffs getting into the property without having to fit an additional vent pipe.

Cheers

[bells]

rosebery... first of all I would like say a big THANK YOU!! for your patience and informative replies.Just to confirm that I have understood your posts... you are saying that in no form can you substitute an outside vent with AAV on its own.You can only use one with the other,and not an AAV on its own... thanks again.
PS, you'll be surprised how many people think an AAV can replace an outside vent.

[bells]

You may be interested to hear this... I contacted two local bco departments today,one said no you can't use a aav on its own.The other said yes you can,and asked me what type of property it was (terrace) where it was in the terrace (mid) and could be sited in main loft space with the polysterene cover on top,this is why I persevered with the post!