Hi, all.
We have a fairly standard '70s internal soil stack, which penetrates the roof. It is capped with a normal open thingy.
Under certain atmospheric conditions, there seems to be a down-draught which causes foul odours as you pass below it. This is unfortunate, because it's also the pathway to the front door.
I'm considering replacing the open cap with a 110mm AIV, to block this. Something like this, perhaps:
Sounds like an updraught rather than a downdraught that is causing the smell - i.e. the air pressure in the pipe is higher than atmospheric pressure.
If you block that escape with an AAV, there's a danger of sink/ washbasin traps blowing through instead and the smell being inside your house.
The building regulations on when AAV's are acceptable are also a bit complicated - could you extend the soil vent pipe upwards instead?
Thanks, I hadn't considered that possibility.
I'm now wondering how the public sewer could be at positive pressure, causing up-draught at my soil stack. I'm trying to thing of possible blockage points etc which could cause this. I'm trying to think of a possible way the pressure could be coming from either the public sewer, or from within the house. I just can't figure such a scenario.
There are other open vents into the system too. There's a second 110mm roof open vent on the newer extension ( en-suite b/room ), and there's an external open vent on the end of the kitchen / util room 40mm waste. These all feed back to the same sewer.
I need to consider the various pressure implications around the system a bit more. I may just try the AAV ( it's juat a push-fit, after all ), and carefully observe the effect on the water levels in the traps.
If you have another open SVP on your property connected to the same sewer then an AAV where you want it shouldn't contravene building regs.
The open vent on your kitchen waste is unusual though - maybe someone has had some awkward issues in the past?
methane is produces in all sewers. Air pressure from the next open stack can,. in a decent wind, produce a significant pressure rise,as can large volumes of loo flush travelling down pipes.
Usually during adverts at prime time.
IIRC The open vent must be on the most upstream stack.
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