Air Admittance Valve

[pizza]

Hi there,

Any experiences with air admittance valves?

I'm refurbishing my bathroom. At the moment the stack pipe takes air from the outside (the roof), an this means that I have a column in a corner of my bathroom. To save space, and why not to improve insulation, I would like to cu my stack pipe halfway (say at basin overflow level) and close it wit an air admittance valve on top. What do you think?

Also, what's the position of building control about this? Is this stuf regulated? I'll ask them tomorrow, but BC in my council tends to answer ver randomly. So I guess if I get an answer I don't like I'll try again :)

Cheers, Julia

-- pizza

[BigWallop]

The main stack is there to keep sewer gases from building up inside the pipes. Sewer gases are very, very explosive and should always be vented to the open air where possible. Closing the stack with an AAV is a very dangerous thing to do, but if your BCO guy still gives you an answer you don't like, then by all means try your idea and find out.

[Mike Taylor]

Whoa there Big Wallop, The vented stacks on your house are there to draw air into the system when you put water down the pipes. It is not there to let gasses out. If air was not admitted then as a column of water dropped down the pipe it would cause a vacuum to be formed behind it and it could and almost certainly would suck dry all of your water traps on that system. Not a good idea in having no water trap in your toilet, waste to bath etc.

[Mike]

So where do sewer gases vent ? If at all ?

I've got a similar and even more inconvenient arrangement to the OP and would love to get rid of the stack to the roof if possible.

[OldScrawn]

When I wor a lad there were iron "chimneys" in the street, about the same height as telegraph poles, I was told they were sewer vents. Havn't seen one for ages though....

[r.p.mcmurphy]

everything's regulated these days... side effect of a Labour government I'm afraid. i cant see much of a problem with it...afaik, as long as your house has another stench pipe, you can use air admittance valves. why at basin level? if i were you id cut as low as poss without interfering with flow etc.

Steve

[General Lee]

If you are going to use an air admittance valve, then why not take your boxing down to 250mm max? Do not forget to also use the anti-vacuum traps on the bath / shower and sink! The bathroom will look much smarter without the SVP stack boxing and you do not have to worry about venting gases. if any gases are ignited in a sewer, they usually just blow some manhole covers off...

Lee

[Frank Erskine]

You still see these occasionally. When I lived "at home" with the parents we had a 1901ish town house with a vent pipe some 8' high from the manhole in the back yard as well as the normal pipe extending some

2' above the gutter on the house.

When I considered fitting an AAV a while ago I contacted the BCO and was told that since I share a sewage manhole with my next-door neighbour who still has a normal "stench pipe", this is acceptable, that is, our communal m/h is adequately vented.

I would _love_ to visit a Victorian-type tunnel sewer!

[Bob Eager]

Got one or two just down the road here (Station Road, Herne Bay, Kent).

They do trips down the Brighton sewers....

[Lobster]

Yes, provided one of these is evident at least every few properties; for buildings in between an AAV alone is OK. When I had this job done some months ago, I had the AAV terminating within boxing behind the bath, but the BCO insisted the pipe was extended upwards into the roofspace, terminating there instead. I think this was a somewhat subjective opinion TBH; it would be worth the OP discussing it with his BCO to see what's considered acceptable; if it's the same as mine there wouldn't be a lot of point in doing the work!

David

[IMM]

Don't be silly. Stop making things up.

See the Building Control dept, Usually every 4th or 5th house requires an open stack.

[pizza]

Thanks everyone.

Though what I'm most interested in I guess is: do these things actuall work? Or am I gonna find out in two year's time that it's leaking fou odours and I have to replace it or worse go through the roof again? Any brands you recommend or I should avoid?

Cheers, Julia

-- pizza

[Andy Dingley]

They're designed to stop vacuums from emptying your waste traps. This much they do.

They're not intended to release over-pressure. So complaining that they don't doesn't really cut much ice.

I can't see myself ever replacing a two-storey stench pipe with one, but they are useful for flat conversions in existing buildings, or even for replacing a single-storey stenchpipe if your bathroom is in a single-storey rear extension to an old terrace.

If you install it in an internal cupboard, then it doesn't need to be deliberately vented (few cupboards are airtight), but it does need to have a reasonably large internal volume.

One day it'll stop working. I've seen them (admittedly only a handful) in service for about 7 years now, and not yet seen a failure.

[Googolplex]

Got one in our back garden. It's at least 50% higher again than eye level from an upstairs window.

The manhole cover in our garden approx 15ft away from the big pole exposes steps down to a very small 3ftx5ft approx "room", with the sewer gully running through the bottom of it.