Pipework for an air admittance valve or stack on a WC

[Chapelgirl]

I have a loft conversion where I want to install a new WC.

The new WC will sit under the sloping ceiling, which is plasterboard on the roof joists, the space between insulated with rockwool. The roof is tile.

The room in which the new WC will be is separated from the eaves-space by a piece of plasterboard. The new WC will sit perpendicular to the run of the joists.

The new WC soil pipe cannot be immediately above the existing one, being about 2 metres away, but I can run a reasonably direct run into it. All the pipework is inside the house, not on an external wall.

I believe I need to install either a stack or an air admittance valve to prevent the water being syphoned out of the other WC pan when one is flushed. The sink wastes etc. do eventually connect into the 100mm soil pipe, but not until they get to the cellar.

I have bought a new Ideal Standard WC with the soil pipe exit underneath, not horizontally.

I believe the AAV needs to be sited above the level of the highest fitting (usually wash basin) to ensure it is effective and to remove the risk of foul water flowing out of the valve if there is a blockage in the system.

In order to join the WC to a pipe going vertically into the room (AAV) or through the roof (stack) I will need some kind of joint which allows a vertical pipe going downwards into the floor to join to another vertical pipe going upwards for the vent, without 'stuff' getting stuck in the join.

(a) what combination of connectors (Y, swept T etc.) would best achieve this?
(b) does the stack or AAV pipe have to be in 100mm like the waste, or can it be smaller?
(c) given that the AAV will be just inside the roof, if you were me, would you use an AAV or would you put the vent pipe through the roof?

Thanks!

 

[Groovejet]

Vent through roof !!.
Once you get your position sorted, cut a "V" slot into the felt, for the soil to go through( This just makes for a neater hole and supposed to help any water run off!!!)
Then once you remove your tile for the flashing to sit ontop, it'll all come clear and should be simple after that.

Where's the existing vent?? In loft space going thru roof??

Because if it is , why are you even thinking about a AAAV install?
Reading the post is it me or are you getting mixed up a little??

The new soil just wants to be tee'd into the existing and thats it.
A 110mm Branch fitting
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[Chapelgirl]

"Where's the existing vent?? In loft space going thru roof?? "

Neither. The existing WC on the ground floor has a side coupling and has a swept T joint on it which terminates in a screw-cap rodding eye immediately beside the pan, so there is neither a stack nor an AAV in the existing setup.

I am planning on joining the new waste into the top of this pipe, or alternatively I could run the new pipe in some box work, straight down into the cellar and join in down there.

This is why I'm asking how to join the new WC upstairs into a pipe I can run as a vent above it.

Because there isn't any vent and because the new WC has to be about 2m further in from the gable wall I can't simply tee into the existing, as you suggest.