Soil vent pipe

[billybuntus]

Hello,

I'm embarking on a project to reduce the soil vent pipe size if at all possible.

The 110mm vent pipe runs from downstairs wc to bathroom then up through the bathroom>loft then out of the roof.

I want to reduce the diameter of the pipe and reroute it the boxing in will be less unsiightly

Can I reduce the diameter or fit aav or durgo to remove the need? I don't think I can but thought someone on here may know?

Thanks

 

[Malc2098]

Hi

I realise it'll take some reading and perhaps a bit more research, but this may be a place to start.

http://www.gov.scot/resource/buildingstandards/2016Domestic/chunks/ch04s08.html

Especially this bit...

3.7.8 Ventilation of a drainage system

A Wastewater drainage system serving a building should be ventilated to limit the pressure fluctuations within the system and minimise the possibility of foul air entering the building. A system should be installed in accordance with the guidance in Sections 4, 5, 6 and National Annex ND of BS EN 12056-2: 2000.

Air admittance valves are another method of ventilating a drainage system as they allow air to enter the drainage system, but not to escape, thus limiting pressure fluctuations within the system. Care should be taken when installing these valves that they are located where they will operate effectively. Air admittance valves should be installed:

in accordance with the recommendations in BS EN 12380: 2002, or

in compliance with the conditions of certification of a notified body.

Hope that helps.

 

[billybuntus]

Thanks.

Makes some sense. Just unsure if I could install air admittance valves and do away with the vent pipe but what I'm actually want to do is fit an adapter post upstairs WC to reduce the stack diamater then joint up to 110mm in the loft space which continues out to the roof.

Building Regulations (H1: 1.28 ) specify 75mm nominal (82mm OD) as the minimum size for a vent pipe.

I've had suggestions to use a durgo valve and a 50mm pipe through the bathroom (vent side from WC) then adapt back to 110 in the loft space.

I don't think it's within regs but once its boxed in who would know? 50mm must surely be good enough to vent?

 

[Malc2098]

I can't answer your questions as I'm only a diyer and would have to research further myself. The little I've done on your behalf talks about the way the AAV works and positive and negative pressure etc and finding the best place to achieve those pressures.

The adverts only show 110 and 75mm products (http://www.mcalpineplumbing.com/media/cat/36.pdf) and so I would have thought a 50mm is not considered sufficient to meet the standard.

I would not want to jeopardise the heath of the occupants by utilising something not proven to work.

I hope other members have better knowledge than me.

Good luck in finding a solution.

 

[RogerS]

Why do you want to reduce the stack diameter? What's the driver to want to do this ?

 

[podengo]

I thinknyou have to be careful that air isnt limited at the end of the system as that can lead to siphoning, which pulls water from U bends.

AAV's are ok but need a minimum distance above a wc.

 

[Mike G]

You really need to talk to your Building Inspector on this. The last leg of a drain run serving the house must......MUST...terminate at a vent pipe outside. You can reduce the diameter of this pipe to 75mm (NOT 50mm) above the level of the highest waste water source connected to the SVP. This is usually the top of the water in the WC cistern. If it isn't the last leg (in other words, you have another SVP further away from the access chamber and the connection to the mains, then you can have a suitable AAV.