Moving WC - Stub stack advise very much required!

21 Dec 2011
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United Kingdom
First post here, usually find most information from searching but this is one where I need a little help.

I am in the process of moving the downstairs (ground floor) wc to the other side of the room. There is also a basin and washing machine going in.

The main stack is ventilated, and you can see from the diagram where the waste exits the house to the main stack (through the wall at low level). There is sufficant drop required for the 3m run of pipe. Will drop approx 20-25cm.

My questions are:

1) Does the immediate 90 degree bend where it comes into the house need an access point? There is already a rodding point immediately outside the house where it joins the main stack.

2) Most stub stack designs I see feed down into the drain, not continue to run horizontally. Can I use this turned on its side: and then feed the wc, washing machine and basin waste into this?

3) Are there any problems with the wc soil pipe needing to turn 90 degrees before going into the stub stack?

4) Lastly, I was going to put a screwed access cap on the top of the stub stack, rather than a durgo valve as its only a relatively short distance to the main stack which is ventiled. I can't see any problems with this?
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Technically you are looking at installing a branch, not a stub stack. (Stub stack would be directly connected to the drain, branch connects to a stack.)

I dont see a problem with what you wish to do, however the branch connection into the existing stack must be a minimum of 450mm above the invert of the drain. The junction is fine on its side, but i'd put a screwed access cap in the open end to provide access should it be needed. Bend immediately inside the house should be ok, access available at the other end if you fit the access cap. You dont need to worry about ventilation on that length of branch.

Need to achieve a fall of about 18mm/m on the branch. Too steep or too shallow a fall and the water will flow away leaving solids behind.

Sink and washing machine can be connected via bosses, into upper wall of the branch.
Ah OK, probably why I wasn't getting far with my searches...thanks for confirming that.

If its not then technically a stub stack, do I still need to run a short section of 110mm pipe to the height of the cistern to stop overflow (where I was going to run the w/m and basin waste into to) or can I run 40mm pipe straight into the junction?

Just to confirm, do I need need a screwed access point at the 90 deg bend just before it goes through the external wall, or is the rodding point outside enough?

Thanks for your help.
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A stub stack connected to the drain would need to be brought up to above spillover level of the basin, but as you are connecting a branch of that length to a ventilated stack it wont be necessary.

Access is up to you, it is better externally (for obvious reasons), worst case scenario could be you have to remove the pan if you cant get to a blockage from the external point. If you are fitting the junction i'd put a screwed access cap in the spare socket, gives you rodding access along most of the branch to the stack then. Lastly, connect the wastes into the top of the 110mm using strap bosses.

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