no venting on soil pipe

[tew1]

Hi,
A few years ago, some building work was done, and the plumber ran all new drains to the kitchen and bathroom, including a soil stack. However, I've realized that he didn't put a vent on the soil pipe (not even an AAV). The stack is last on the line of the drains. Obviously, there's problems with traps being pulled, when the washing machine drains downstairs it does nasty things to the toilet upstairs e.t.c. The shower and sink are the main problem-whenever you drain the sink, the traps pull.
The bathroom is all finished, but I'm completely redoing the bedroom next to it, and it would be VERY easy to extend the 40mm drain from the shower and run it up the wall into the loft and out of a flashing on the roof (the RED pipe in my picture). Will a 40mm vent stack alleviate the venting problem considerably, or just cause worse problems that I haven't considered? I know it is the norm to use 1 1/2 vent stacks in other parts of the world, but it't usually a 4 inch one in the UK.

Untitled

• tew1
• 23 Nov 2013
• 1

 

[nyck]

To test your idea You could drain the water from the Shower trap only so its acting like the vent .Then see if the other traps pull when you empty the sink,washing machine etc .If they dont then extend the pipe .

I'm just a DIY'er so i dont know the rules and regs but i thought you could try that before you done the actual work

nyck

 

[Hugh Jaleak]

Ideally needs to be a 4 (or even 3) inch vent pipe, but fitting a 40mm as you propose can only help the situation. However, if the washing machine is affecting the WC upstairs there may be something more serious wrong. A 40mm pipe from a washing machine, even running full bore, should not be sufficient to cause a problem with a 110mm soil pipe to a WC.

 

[tew1]

Ideally needs to be a 4 (or even 3) inch vent pipe, but fitting a 40mm as you propose can only help the situation. However, if the washing machine is affecting the WC upstairs there may be something more serious wrong. A 40mm pipe from a washing machine, even running full bore, should not be sufficient to cause a problem with a 110mm soil pipe to a WC.

There is one soil stack that serves everything, and there is no air behind water, so, when the washing machine is draining downstairs, it is displacing air in the soil stack, causing turbulence in the toilet upstairs. If you flush the toilet whilst the bath is draining, it's like a bottle emptying, it needs to pull air in from just below where the water is discharging (the boss), therefore, the upstairs sink and shower traps are pulled, so, in whatever situation, air is passing through the 40mm pipe serving the sink and shower to the soil stack. This is why I'm thinking if I just extend this pipe up and out the roof, it'll continue doing what it's doing, but you won't get any pulled traps. Is this right?

 

[Hugh Jaleak]

I can understand whilst flushing the WC a problem could occur, the WC can fill the 110mm pipe briefly and cause a vacuum behind the flush water, but for a washing machine to fill the 110mm pipe under normal circumstances should be nigh on impossible.

This issue could arise if there is a partial blockage in the underground drain, which would account for the washing machine filling the 110mm pipe and causing the air bubbles in the WC. Have you got a manhole/inspection chamber where the 110mm drain from said stack connect into the drainage system?

 

[tew1]

but for a washing machine to fill the 110mm pipe under normal circumstances should be nigh on impossible

It's an industrial sized washer with a 40mm drain hose, so it's probably a similar flow of water to flushing a toilet. There aren't air bubbles, just turbulence, I know what you mean about a blockage, I'll check the manholes, but, probably the reason is that the manholes are all the screwed-shut airtight type, and there is no vent stack anywhere on the line to release air. All the volume of water entering the stack downstairs needs to displace the air in the pipe, and there's nowhere for it to go except toward the main sewer, which is probably full of water. There is an AAV on a stub stack further along the line to allow air in (closer to the main man hole) but nowhere for air to escape. This is the only reason I'm wary of the 40mm vent, because it will effectively be the only point of air release for the entire drain system (including all the outside gullies), although I can't see any reason it would cause a problem. In the US and Aus 2 inch vents are standard for soil stacks, so it must work.

 

[newbuildinstaller]

put anti siphon traps on all basins, showers and even the wc

 

[tew1]

put anti siphon traps on all basins, showers and even the wc

anti-syphon traps only let air in, they don't let air out, that would be smelly! I've already said the bathroom is finished, I can't rip out the bath, toilet and shower to install new traps, but I can vent the 40mm drain to the roof effortlessly, just want to know if it will work

 

[denso13]

just want to know if it will work

Don't think anyone can tell you that categorically. It should be a minimum 75mm diameter though to comply with the regs.