Air admittance valve instead of vent stack

[JOEPRO]

Having designed hundreds of houses and properties I have never ONCE specified an air admittance valve.

The odd time a contractor installed one anyway it ended up stinking the place out and having to be re done.

They are a band aid at best and soil stacks should be correctly terminated above roof at all times. No exceptions.

 

[DAPPH]

Being in a bungalow on a long steep hill with lots of homes either side up & down the hill , we had a 2.5 inch dia stink pipe on the outside , it poked just above the gutter and by heck did it stink the place out when the rain water joined the sewage system.
The garden used to get water logged so I hired a mini digger , removed all the paths, inserted five runs down the garden , back filled with bark chips .... using 130 meters of perforated land drain .

I've also put in sealed plastic manholes every 7 mtrs as my 2000 psi power washer drain cleaning jet hose can sort that distance out no problem .

I added a simple 110 mm stink vent to the final external end , gosh I never realised just how important the air over water situation is . The toilet emptied like Niagara falls where as previously it was very sluggish , often requiring a second flush .

 

[brightspark]

i fit one in the downstairs bog but the 2 upstairs bog stacks go out through the the roof

 

[Seadog]

 

[hermetic]

The problem with AAV's is that the system needs to be able to withstand a vacuum sufficient to open the AAV without emptying the traps, low level bath traps have very little weight of water in them, and sometimes it can be a toss up wether the AAV opens or the bath trap empties, with smelly results! The answer is to fit a deeper bath trap! these things are a comprimise at best, and can be a nuisance.
Phil
"Phil Whitley,my week this week" on Youtube!

 

[Seadog]

The whole point of an AAV is that you don't get suction, even with a full bore flow.
I never use water traps. A hot summer and long holiday equals dry traps and smells.

 

[JOEPRO]

View attachment 462978

Great example of a completely wrong installation!! Regs do not permit what is shown here.

 

[Seadog]

Great example of a completely wrong installation!! Regs do not permit what is shown here.

Why?

 

[Smouser]

Having designed hundreds of houses and properties I have never ONCE specified an air admittance valve.

The odd time a contractor installed one anyway it ended up stinking the place out and having to be re done.

They are a band aid at best and soil stacks should be correctly terminated above roof at all times. No exceptions.

I wish our house had an outside stack.
Constant struggle with a silly air admittance valve.

So fed up with it, I am going to sell my house.

 

[JOEPRO]

Why?

Any drainage ventilation pipe should discharge minimum 900mm above any opening. So the termination below a window in you photo using a AAV would be rejected by most building control officers.

Building control technical booklets are guidance documents only and AAV's are permitted if compliant with BSEN12056:Part2 and BSEN12380 but It is a matter of interpretation and as said most Building control officers will reject an AAV and ask simply, why not extend it up to the correct height and remove all risk?



It is not best practice and an AAV would require ongoing maintenance to ensure it does not pose a risk.

Where a correctly discharged vent stack will never require any maintenance or fail. The gases will safely disperse. In most cases if there is a roof soffit nearby then you crank it out and terminate above the gutter line to avoid negative air pressure.

It is amazing how far the gases can travel, even along facia boards in an installation that isn't taken high enough.

 

[Seadog]

It's about 1.5m above the waste entry and 200mm above the basin level in tge bathroom.

 

[JOEPRO]

It's about 1.5m above the waste entry and 200mm above the basin level in tge bathroom.

it's also terminating below 2x window openings!

That's the issue. You are reliant on the AAV functioning impeccably to not have gases coming into those rooms. Which will happen the moment the AAV fails.

Wheraes if the soil stack was extended on up above those upstairs windows then the gases can safely vent away to atmosphere and there is no need for an AAV at all.

 

[Seadog]

But that is for is normally vented stack.

 

[JOEPRO]

But that is for is normally vented stack.

Did building control sign off that AAV?

Or is it a DIY installation?

I don't think you are understanding what I'm getting at which is OK. I'm trying to help is all. AAVs are not used anywhere in most buildings for good reason.

Another thing no one considers about AVVs is that they don't do anything about back pressure in system this can also push smells through traps and into the room.

 

[Seadog]

It's an installation that works. Building control?

 

[JOEPRO]

It's an installation that works. Building control?

It works for now...

Not how it should be done. It's an example of how not to do it.

Not targeting your photo just offering the forum members advice based on extensive technical expertise and also having investigated issues with gases entering buildings and resolving them.

I recall cases where the family members were actually ill because of poorly conceived systems and had immediate relief when something in my opinion was painfully obvious was pointed out and rectified.

 

[sg66]

I had a friend who did a half self build, he bought a shell basically, one of the things he got a no for was an aav incorrectly positioned below a window, he had it inside to start with and after that was denied he stuck it outside just above the tee and they came back and still said no.

 

[hermetic]

The whole point of an AAV is that you don't get suction, even with a full bore flow.
I never use water traps. A hot summer and long holiday equals dry traps and smells.

it is the suction in the system that opens AAV against a spring or tensioned diaphragm, until the tension is overcome, a vacuum develops and a low bath trap will sometimes empty and thus the AAV will not open. They are not a perfect solution, especially after a few years of plastic aging! mine works about 20% of the time, the rest it empties the lowest trap, the bath! I should of course fit a deeper bath trap, but due to my fil's insistence on tiling perfection, getting back under the bath is virtually impossible!
Phil

 

[JOEPRO]

it is the suction in the system that opens AAV against a spring or tensioned diaphragm, until the tension is overcome, a vacuum develops and a low bath trap will sometimes empty and thus the AAV will not open. They are not a perfect solution, especially after a few years of plastic aging! mine works about 20% of the time, the rest it empties the lowest trap, the bath! I should of course fit a deeper bath trap, but due to my fil's insistence on tiling perfection, getting back under the bath is virtually impossible!

There is a bit of science to that and here is a summary FWIW:

 

[JimmyS]

The branch discharge pipe lengths above are to stop the traps being pulled by self syphonage ie the whb emptying and the trap getting pulled by the water leaving the whb for single pipe systems. If bath trap is getting pulled then it's prob when bog flushes and durgo is not working. We spec durgos some times and will use loop vents at times to vent stacks but durgos generally seem to work well enough. I try and stay away from the dark art of sh1t pipe sizing though, I hate it lol.