Internal air admittance valve

20 Aug 2013
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United Kingdom

I live in a two story building and the 110mm soil pipe from downstairs runs up through my flat (in a huge pipe box) and up and out roof. The person downstairs toilet uses this as a vent and my kitchen also drains to this soil pipe.all other plumbing uses a soil on the other side of building.

I am fitting new kitchen and want to get rid of pipe, so I plan to fit an floplast air admittance valve. (I want to hide the pipe in a kitchen cupboard)

Question: can I reduce the pipe to 40mm and use a 40mm AAV or do I need to use the 110mm one. The 40mm one is 6.5 l/per sec The 110mm 43l/per sec.



Should have read document H.

1.32 Sizes of stack ventilation pipes – stack ventilation pipes (the dry part above the highest branch) may be reduced in size in one and two storey houses, but should be not less than 75mm.
1.33 Ventilated discharge stacks may be terminated inside a building when fitted with air admittance valves complying with BS EN 12380:2002. Where these valves are used they should not adversely affect the amount of ventilation necessary for the below ground system which is normally provided by open stacks of the sanitary apipework.
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I wouldn't want an AAV in my kitchen and would not fit one for a customer. If the stack is properly vented through the roof, I would try and work round it.
Stack is vented for a reason, I would also be unwilling to remove the vent and fit an AAV. You could well find it causes more problems than it solves....

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