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:
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.
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.
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