Bathroom refurb, questions on soil pipe modifications and using air admittance valves

[BuffetSlayer]

Hi all

We will be refurbishing our bathroom imminently and I have a couple of questions regarding soil pipes.

Currently, our house has a soil stack from the ground floor kitchen and it passes vertically right through the house and it vents out of the roof.

The pipe passes through the corner of our bathroom, which is very modest in size and we are losing almost 1sq/ft to the boxing in the corner that houses the soil pipe.

My question is does it need to go through to the roof and vent externally, or can I:

• Cut the soil pipe below roof level in the loft space and cap it to prevent water ingress (saves me having to mess around with the penetration through the roof which is currently water tight)
  
• Remove the section of soil pipe from the bathroom junction up, including the junction itself. Then install new junction and a short piece of soil pipe and cap it with something like this http://www.screwfix.com/p/mcalpine-vp100n-solvent-weld-air-admittance-valve-grey/6047p
  
• Enclose the area with some timber batons and a choice of finish, incorporating it into our toilet / basin vanity unit design so that it remains concealed.

Additionally, if this is possible, what is the correct height from the junction point for toilet and basin wastes to install this? Ideally, to create a seamless worktop on the vanity units I would like to bring the whole soil pipe section (including waste junction) to around 840mm high. That would allow it to sit below the level of the worktop and have a 12mm clearance above it.

Does anyone know what sort of clearances these air admittance valves require?

I would greatly appreciate your advice.

EDIT - added a basic picture to try and make sense of my descriptions!

 

[the_r_sole]

aavs are usually used where you have branches into a stack rather than for the stack - I believe the stack needs to vent to outside air, or have at least one vent to outside air on it
They should be above the highest waste in the line, (usually the overflow for a whb)

 

[Dis86]

Stick a durgo valve on it.

 

[a1ex2001]

Your fine having no external vents I know several people that use aav's following extensions etc be prepared for the funny noise!

 

[kinobestew123]

When I read your post, I thought it was a post I'd made and forgotten about. What you've described is EXACTLY what we're currently doing.

We had our chosen bathroom fitters around and I was talking to them about how the box for the soil stack takes up so much of our small bathroom. When they sent us the quote, they added on there "fit air vac" or similar. I phoned him up and questioned what it was and he explained that it would get rid of the soil stack above about 800mm which means it will sit below our countertop. We'll use a filler panel to box it in then next to the toilet cistern unit.

They plan to leave the upper piece of soil stack sticking out of the roof but capped. In the future we'll remove it when we have a new roof anyway.

The actual workings of it I'm not sure about but they seemed to think it would work. It would be great as not only would it remove the unsightly stack from the roof but it would also make better use of space in the bathroom.

 

[the_r_sole]

interesting - I've always been told that the stack must have an outside air vent as this lets gas both in and out, an aav is a one way vent.
If it was to be signed off by building control replacing the outside air vent with an aav would not be allowed - it would be worth confirming with your local authority that this is acceptable before bashing on

 

[BF-Bert]

Valve has to be set higher than the highest waste outlet...... which is usually the wash hand basin overflow. If it is boxed in then the enclosure needs vent holes.

 

[LOAM]

The head of the stack should be vented, this means the last connection on the run. On your picture, It depends on which way the foul is flowing below ground.