Minimum soil pipe vent diameter

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Re routing a soil pipe so the vent will be concealed behind sloping ceiling plasterboard between the roof joists.

Two questions.
Will AAV work with the 110mm vent pipe at 45 degrees?
If no, could I remove the valve, step down the 110mm pipe to 40mm and extend into the loft space. Would a 40mm AAV be necessary / preferable in the loft space or leave open? I can't extend the 110mm pipe past the roof joists but 40mm will fit.

Thank you!
 
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I've known a rainwater pipe used as a vent,running up next to a front door, into the soffit and out the roof because it matches the RWP @ the other end of the building;) AAV won't work on an angle- vent through the roof to open air and use a rubber/lead slate.
 
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Thanks Nige but breaking through roof not an option....wife....aesthetics. ....will vent into loft space with 40mm AAV I think.

Thanks for confirming AAV on angle won't work
 
N

Newboy

32mm minimum in the dry section of the stack and make sure that the AAV is accessible.
 
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I thought the dry section could only be reduced to 75mm ?

thought so.

vent.jpg
 
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75mm is the correct book answer.

This covers all 110mm single SVPs including 4 or five storey or more jobs with multiple loo flushes simultaeneous at different heights.

I bet that 50mm, and wouldn't be surprised if 40mm, suffices for air movement in the dry portion of the stack in most domestic situations.
 
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If it's currently an open vent, I would strongly advise you do not cap it with an AAV, or you may find you have problems, apart from contravening the Building regs....
 
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If it's currently an open vent, I would strongly advise you do not cap it with an AAV, or you may find you have problems, apart from contravening the Building regs....
At present it has 110mm AAV, but I need to move this pipe and conceal / reroute between roof joists which are angled at 45 degrees. So I intend to remove 110mm AAV, extend vent pipe into loft space by using 40mm pipe, I can then add elbow to make it upright again enabling a 40mm AAV to function in attic.
 
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