soil pipe alterations in bathroom

[src1]

We are currently working on our bathroom and have a soil pipe that runs from the toilet along the floor to a down pipe in the corner of the room where the waste drops. The pipe also goes up into the loft and vents from the roof. We would like to use this space to install a cupboard so to max the space available there are 2 options that I am aware of,
reduce the size of the pipe or install an air admittence valve.
The valve would provide us with the most room but Im a bit concered that it may fail or allow dirty air to seep. I am new to DIY and my knowledge is developing as I build my understanding so please bear with me.
I have attached a photo to help

 

[dontknowitall]

A Durgo should be fine - if memory serves me correctly it has to be 1 metre higher than the highest waste pipe/pan connector.

If you're worried about having to replace it, you could install it near the ceiling (I'm assuming the cupboard is upstairs) and leave an access hatch in the floor above so it's a fairly easy job. It should last for a good few years though but best practice would be to give it access.

 

[src1]

Thanks for the reply. The cupboard is for the bathroom and i would be installing the valve as low as possible. Hopefully under the bathroom unit work top, From upstairs the toilet is the only connected thing so from your reply the recommendation is 1 meter above the toilet outlet which might impact on the bottom of the cupboard but thats no a big deal. So they only last a few years, i wasnt aware of that. Is there any reason why I cant use a reducer? and then let it induce to a larger pipe in the loft?

 

[Essex Fitters]

I believe you have two options. Both expensive..

1. from under the floor elbow out throw the external wall and then run up to a open vent.
2. use a durgo for the down stairs WC and install a sani-flow for the 1st floor WC. (pipe work can be as little as 22mm)

Can you not build around the boxing, make some fantasy shelving?

 

[carpstu]

dont think id introduce more hassel by adding a sani-flow i would just like u say 4 inch core drill through the wall an up the out side with the air/soil pipe (meter above any opening window) or as said a durgo boxed in meter above nearest pan connection

 

[Spike295]

The durgo valve only has to be higher than the highest spill over level of any appliance connected to the drain. In your case, if it is only the wc connected to the soil stack, then the durgo only has to be higher than the rim of the wc pan. If you had a washbasin also connected to the stack, then the durgo would need to be higher than the washbasin overflow.