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.

The message

from Jonathan Tong contains these words:

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.

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.

--
Roger Chapman

Roger wrote:
The message

from Jonathan Tong contains these words:

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.

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.

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

On 12 Feb, 02:05, The Natural Philosopher wrote:
Roger wrote:
The message

from Jonathan Tong contains these words:

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"?

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

http://www.planningportal.gov.uk/eng...000000382.html

In 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!

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.


"Jonathan Tong" wrote in message
...
On 12 Feb, 02:05, The Natural Philosopher wrote:
Roger wrote:
The message

from Jonathan Tong contains these words:

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"?

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

http://www.planningportal.gov.uk/eng...000000382.html

In 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!