82mm vs 110mm for soil vent to AAV



Hi all, any advice appreciated pro/against - thoughts invited please.

Refitting a bathroom, floor is up and full access to underfloor. Soil will run 2,0m from toilet to a 90bend into vertical stack. The washbasin waste will enter soil at midpoint with bath entering just prior to the 90bend.

Intending to use 110mm soil pipe and should be able to get a 10cm fall over the 2.0m run. here's the questions inviting thoughts/advice.........

Immediately upstream of the toilet entry I intend to put a 90 bend to the vertical and then a vent-stack to an AAV.

1. Prefer if poss to have a reducer to 82mm (for space) and then a 20cm pipe to a 82mm Flopast AAV (cos they say it can be fitted below highest flood point). Is this sensible?

Is the 82mm vent and AAV sufficient?
Is it right that the AAV can go below the max flood height?
Would it be better to have a full 110mm vent up into the loft with an AAV or is this over doing it?

many thanks in anticipation.

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An 82mm vent will do fine and if the manu says the AAV can be fitted below flood level them that is fine too.
The problem may lie with your 10mm drop over 2m (1:200) Get a bit more if you can and also try to put an access pipe somewhere just in case :idea:
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Bear in mind that AAVs are a supplement to the open vent to your soil system, not a replacement. They admit air if the pressure in the part of the system they are connected to falls to prevent syphoning, but they do not disperse any increases in system pressure.

Sometimes AAVs are fitted inappropriatly, causing problems in the rest of the system.

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