minimum diameter of soil pipe vent?

I've currently got a soil stack that serves a WC & sink in the downstairs cloakroom and a WC, sink, bath and shower upstairs. The soil stack currently vents to atmosphere through the roof.

Above the level of the WC I'd really like to reduce the diameter of the vent to as small as possible so that I can go round some tight corners before re-joining with the existing roof vent. I do not want to use a dergo AAV.

What is the minimum diameter of *vent pipe* that I need/must have? I believe that I can go down to 3" pipe, can I go smaller to say 2"?

TIA for any advice.

Reply to
Jonathan Tong
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from Jonathan Tong contains these words:

I think you will find the minimum diameter is 2.5 inches or thereabouts. I went down this route a few years ago on a loft conversion and am sure I had to up the pipe diameter from my original choice of 2 inches. No idea where exactly the limit is enshrined though.

I have looked at my drawings and I definitely specified 2.5" (63.5mm) pipe in the final version.

Reply to
Roger

I went to three and routed it miles to find a decent exit point.

Reply to
The Natural Philosopher

I eventually found a copy of the relevant building regs (part H) online:

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part H1 - 1.28 it states that the minimum for a one/two storey house should be at least 75mm (3") - so that's what we're going for.

Thanks for all your replies!

Reply to
Jonathan Tong

I was recently asking this question to my brother who was a plumber/builder as I have a OsmaVent AAV in the bathroom just where I want to place a bigger bath.

He says leave 110mm if poosible, but you are allowed to go to 50% of area of

110mm (80mm?, I think 82mm is the availlable size) for the vent stack but if you have issues with traps being sucked through it is hard to rectify after the fact.

He has seen a bath trap being pulled through (and venting sewer gas) due to toilet flush where the builders had reverted to 50mm vent pipe due to fitting a posh new bathroom suite. My brothers fix was to route the 110mm pipe up a bit inside a fitted bathroom cupboard and right angles out through external wall to an external vent.

Reply to
Ian_m

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