Hi, This is my first posting on this forum. I live in Derby, UK.

I need a bit of advice with regard to an air-admittance (Durgo) valve on a toilet installation. I am re-locating the soil piping for a new toilet at the opposite side of the bathroom, requiring a new soil pipe to be laid under the concrete of the bathroom floor. There is an air-admittance valve connected to the soil pipe just above ground level in the current installation. Due to space restrictions, I want to put the new AAV on the end of a length of 2 inch pipe, and run this pipe vertically through a stud wall. The problem I have is making the connection to the new soil pipe, due to space restrictions.

It has been suggested to me that I connect the AAV pipework directly to the pan connector, (as these types of fittings are readily available) instead of to the soil pipework itself. The AAV that is currently fitted is a 4 inch device. I have been told that AAVs are available in many sizes. The pan connector that was shown to me has a compression fitting for a 1-1/4" waste pipe.

My questions are :-

Are there any regulations (bylaws etc) stipulating what the minimum size of AAV is needed for a toilet installation?

Are there any recommendations, or rules-of-thumb for sizing the AAV, or does it not matter in practical terms?

Cheers for any opinions on this one.

Regards,

Rob

Yes to everything but 3" is the smallest you can go down too.

Is this a secondary stub stack vent or the main svp.

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The present installation in the only soil pipe installation in the house. It is entirely internal, and the AAV was hidden under a vanity unit for the wash basin. It collects tha waste water from the bath and wash basin, but is lower than the P-trap of the wash basin, so it is actually too low.

The kitchen waste water exits the building via a different waste system, and empties into a different gully.

The new installation will also be the only soil system in the house. It will collect the waste from the bath and wash basin. I want to ensure that the AAV is out of sight, but high enough to be above all other waste system pipework.

What is(are) the limiting fastor(s) on the size of the AAV? Is there a building regulation or water by-law that relates to this? Why three inches?

Cheers,

Rob

At least the head of the drain must be vented to atmosphere.

The regulations say 3" is the minimum size for the vent that goes to atmosphere.

Look up approved document H and inwardly digest.

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Hi, again,

I have read through the relevent part of part H of the building regulations 2002, and found the reference to the 3 inch minimum stack vent pipe on page 11, Section H1 (Sanitary Pipework) paragraph 1.32. Cheers for the info...

I did have a question relating to the comment that you made in you last post. When you say "...head of the drain...", do you mean the part of the system outside of my house? The present system has this AAV on a short stub in the bathroom, but this then disappears into the ground and connect to the drain outside. I have lifted an inspection cover and seen a common collection point for my property, and (I believe), the house on the other side of my fence. I do not know of the whereabouts of any open vent on this external pipework in my drive. Nothing else is fitted inside my house. It's just 2 metres of soil pipe and an AAV, straight out to the sewer.

Should I be fitting an additional open vent that terminates externally to the property to prevent "back pressure" in the WC waste? My property currently does not have one. It was built in 1993, and I am the second owner. I do not believe it has been modified since it was built.

Can I assume that the building contractors have arranged for appropriate venting to the sewer system outside my property when this estate was built?

Cheers,

Rob

If the neighbour connects into the same chamber, can you see if he has a vent sticking up or through the roof.

Two or more properties could share a vent when they are using the same drain.

It's in Doc H somewhere.

The vent to atmosphere is nothing more than to take the gases from the chamber, you don't want gases building up and going bang.

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Hi, again, Scruff,

I have seen different descriptions for AAVs. If I am fitting an AAV to the stub-stack for my toilet, does the AAV need to specifically designated as a "soil pipe AAV"? I have seen some described just as "AAVs", and another one as "110mm soil pipe AAV". Is there a difference? This AAV is intended to be dry, and the AAV siting will be above te highest flood/overflow level in the house.

Additionally, the current (undersized) AAV that I have bought from PTS is going to be exchanged, but PTS do not do soil pipe fittings, only "above ground" and gas stuff. Does this mean that an AAV from them will not be suitable, even if it is the correct size (i.e. >75mm)?

Cheers,

Rob

An auto air admittance valve, is designed for internal use.

PTS sell above ground plastic soil pipe and fittings which is what you want.

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