Soil stack vent reduction

[tommy8884]

Hi all. I'm mid way through a bathroom renovation. As part of this I will be moving the T on the vertical 110mm soil stack down into the 1st floor void (its above floor level at the moment). The stack currently vents up through the loft and out of the roof. As part of this, ideally I want to remove the vent so we don't have it boxed in in the adjacent bedroom, as it take up valuable space. Ideally id like to reduce the vent size down to 50mm so it can be inside the partition wall which has 76mm depth. I would then terminate in the loft with an AAV. So my question is, am I allowed to reduce it down to 50mm just for the vent, or does it need to be 82mm waste, which i could achieve with padding the wall out a tad, but the 82mm pipe is expensive.

For info there will be 1 toilet, 1 sink, 1 shower and 1 bath all into that stack from the same bathroom. The other downstairs bathroom and the kitchen go directly into the ground, no vents.

 

[Wayners]

Check with building control help line.( Just phone them)

I think you can unless local laws say otherwise. I haven't seen 50mm myself but not really my area of knowledge.

 

[tommy8884]

thanks, I think i will go with it having done a bit of research. I will probably add further AAVs on the sink and bath wastes in line, just to minimise the risk of the traps having their seal broken. Incidentally |I have that issue on a downstairs shower that was fitted to a downstairs loo, which has no vent (that was done in 2007 long before i moved in).

The rest of the houses on the street are open vented, so no issues there. I will notify building control so they know in case everyone starts using AAVs

 

[Hugh Jaleak]

Strongly advise you do not remove an open vent, it is there for a reason. AAV's have their place, but fitting one to a previously vented stack, may cause more issues than it solves.

 

[tommy8884]

Strongly advise you do not remove an open vent, it is there for a reason. AAV's have their place, but fitting one to a previously vented stack, may cause more issues than it solves.

Thanks. What sort of issues do you think I could have? I have read that I can remove it as they are only needed to let air in and prevent a syphoning not to actually vent the bad gases out. All my neighbours are vented so no issues there.

If a major issue I could always go back up to 110mm in the loft and use the existing vent. I was hoping to remove it as it currently leaks and I could do with a vent exit point for an extractor

 

[Hugh Jaleak]

AAV's will relieve Negative pressure, i.e. allow air in, however under certain conditions, positive pressure can be created within the system. If this pressure cannot escape, it'll look for the easiest way out, which is usually a shower, bath or basin trap, giving rise to gurgling issues and obnoxious smells.