venting question - using old empty outdoor SVP as air vent

[OIC9229]

Hi all,

I have an old toilet on the top floor (to be removed) which empties into an outdoor vertical SVP and into the ground. The pipe is straight with a vent terminal on top.

Another toilet on the ground floor empties through the suspended timber floor into (what I suspect) a drain.

I wish to create internal vertical SVP going through the floors at the corner of the house from underneath and vent it through the outdoor SVP via loft, removing the upstairs toilet. However, in order to do so the 110mm pipe will have to go to the ceiling of the top floor into the loft and then connect to the new stack in the loft.

The entire drainage will be through the new indoor soil stack into the underground drain in the foundation of the house. For the air, the stack will then go through into the loft, come back down from the loft to the position of old toilet, get out through the wall into external stack where nothing else is connected except the outside vent terminal.

Will that work? Is it allowed?

 

[Knappers]

Why not just fit a durgo valve?

 

[OIC9229]

Why not just fit a durgo valve?

it would interfere with insulation in the loft space as it would have to pass through the insulation when a 110mm air pipe would go under it between loft joists with insulation on top. I know that air admittance valve might work, but looking at this solution as it would solve allot of other possible issues

 

[Knappers]

I can't see why it would be a problem, it's a bit unusual to say the least.
Durgo wouldn't need to go as high as the loft, it just needs to be a set height above highest overflow level?