Soil Stack Design Help

[William Rowe]

Hi All,

I'm at the stage of putting the waste plumbing in my extension, just hoping for a bit of advice around plumbing the wastes into the soil stack.

I'm running all the wastes and soil individually through the outside wall under the floor, so they'll all emerge along the same plane outside, so just looking for advice on how I should best plumb these into the soil stack.

I have attached a diagram of how I think I could do it, however there are a few questions:

1. Is it OK to merege the Sink, Bath and Shower wastes like this?

2. Do the fittings even exist for this arrangement? - I know you can get a 135 degree T but I think that would give the waste branch a 45 degree drop which I don't think is suitable.

3. Is there a specified order at which soil and waste should enter the stack - ie: can grey waste enter underneath soil and vice versa?

4. Is all this completely wrong and there is a much better way?

Any advice gratefully received.

Cheers,

Will.

 

[Hugh Jaleak]

Using a 92.5° Junction would be a better option if you can for the WC, gives 2.5° angle on the branch pipe, which is ample fall. Can use a 135° junction but it could result in unwelcome noises when the contents of the pan hit the vertical section of the stack at some speed.

Wastes, ideally run them separately, if you cant, strongly advise bath and shower are separate, have seen what's happens when a full bath is let go and it comes back up through the shower.... If you must combine them, use 50mm waste pipe after the last connection.


Wastes can enter the stack at more or less any point, the only restrictions are opposing connections within the area 200mm below the centreline of the WC branch, to prevent crossflow.

 

[William Rowe]

Hi Hugh,

Thanks for that, yeah I think I'm fine with the soil, it was the three wastes I was debating. It sounds like I was right to question combining them then, I wondered about backflow just didn't know if I'd get away with it if I ran them far enough separately before combining for the stack. So running separately into the stack is best option, ie 3 separate branches. Sounds like a plan, thanks.