Soil Stack

[bcfcjwb1]

Hi,

I'm in the process of designing a new layout for our bathroom and have a question about soil stacks.

My house has a downstairs cloakroom, main bathroom and ensuite. The bathroom and ensuite both have soil stacks that go into the loft and have insulated air admittance valves. I'm not sure about the cloakroom.

I was wondering if it would be possible to reduce the height of the existing soil stack to the same height as the bathroom units. This would help with the design and make things look tidier.

We have never had any problems with drain smells or blockages, so if there is any risk of problems I will leave things well alone and work around the existing full height soil stack.

Any advice gratefully received.

Thanks in advance.

 

[Murphtek525]

as long as your AAV is above flood level then your ok, so above the height of your basin which is generally the highest waste point.

 

[bernardgreen]

You must have one vented stack that vents outside the building. Air admittance valves allow air into the stack to ensure that water in the traps ( U bends ) cannot be sucked out of the traps by low air pressure in the stack. They do not allow over pressure air to escape from the stack, That air and the sewer gases escape from the external vented stack

 

[bcfcjwb1]

Hi,

Thanks for the replies so far.

I can find no evidence of a vented stack anywhere - the house was built in 1998, does that make a difference?

Also, the plot thickens:
​

I've had quotes for the work from 2 plumbers I've used before.

One said no way would they reduce the height of the stack, it's too much of a risk if everything works well now...the other said they would definitely cut it and there wouldn't be any issues!

Confused. Anyone else got any strong opinions

Thanks again.

 

[OvertonPlumber]

At least one stack per drain run should be vented to atmosphere at high level or via ridgetile adapter. As said stack should be above flood level i.e highest waste. With a dirgo (aav) system it is very easy to get suction on the drains. Apparently hepvo valves can balance the pressure but never seen it fix it.