Getting a WC and bath waste into the same branch pipe

[lineweight]

Is there a proper, or best, way of doing this?

 

This situation arises where you want to have only one pipe emerging through an external wall, but you want to connect multiple appliances into the soil stack. And where you can't run the horizontal branch under the floor, and drop each appliance vertically into it.

 

Is the solution to run them to a soil manifold, then there is a bend immediately underneath the manifold which takes the pipe horizontally through the wall?

 

Or are there any other options?

Edited December 21, 2020 by lineweight

[TonyT]

Have a look in here.

 

https://mcalpineplumbing.com/

 

There will be a solution in there!!

 

 

[lineweight]

8 minutes ago, TonyT said:

Have a look in here.

 

https://mcalpineplumbing.com/

 

There will be a solution in there!!

 

 

Thank you but I already have!

 

The question is more about what's allowed or considered best practice.

 

I've not found any products that are specifically aimed at the situation I describe - the "Soil Manifold" sometimes also known as a "Collar Boss", as I already mentioned, is the one that comes closest.

 

Even a close reading of Approved Document H, as well as BS 12056, doesn't throw much light on what is or isn't supposed to happen, if I want to connect a WC and a bath into the same branch pipe. I can't see anything that explicitly forbids it, but nor can I see anything that mentions it as a scenario that might arise.

 

 

 

 

 

 

[TonyT]

I have my sink inch and a half connecting into my WC both connecting into the same 4”. The bath then connects to the 4” at the end of the pipe.

no probs

[TonyT]

Just make sure the runs are correct and pipework is installed properly and you will have no issues.

 

my layout helps maintain clean pipework, as you flush the toilet then use the sink putting extra water down after the flush.

 

 

 

 

[joe90]

@lineweight I think a drawing of your situation will help, I don’t believe there is one solution, just depends on what and where.

[Russell griffiths]

You need to explain more what you are trying to do and what reason. 

 

Is it a new build .?

is it just a bathroom Reno 

why through the wall.?

what is on the other side of the wall.?

are you at ground level or first floor. .?

blah blah blah. 

Theres a million ways to skin a cat, 

[lineweight]

Essentially these are the two options I'm looking at.

 

Top one, waste pipe is laid from WC2 to a "soil manifold" type connector at the most gradual gradient allowed and connects in as shown. Then, waste pipe from Bath2 can run at a slightly steeper gradient and connect in as shown.

 

Bottom one, waste pipe from bath2 is laid as shallow as is allowed, then drops into a simple boss connection on the larger pipe, which is near horizontal at that point. Then, the larger waste pipe starting from WC2 runs at the steeper gradient, to whatever that level has to be.

 

The bottom option seems the more straightforward. But is it ok just to drop the 'blue' pipe into the 'red' one like that, and if so does it have to go in the top or can it just go in the side (in which case the main pipe might barely have to drop below floor level).

[lineweight]

4 minutes ago, Russell griffiths said:

You need to explain more what you are trying to do and what reason. 

 

Is it a new build .?

is it just a bathroom Reno 

why through the wall.?

what is on the other side of the wall.?

are you at ground level or first floor. .?

blah blah blah. 

Theres a million ways to skin a cat, 

 

Sure. It's 2nd floor at loft level. Loft extension. Messy/difficult to drop into room below. There's really only one external wall that it can exit through because of drain positions and other stuff. The reason I'd like to just have one pipe pass through the wall is that the wall is actually part roof/part wall and what's going on just there is already pretty complicated in terms of flashings, structure and so on.

[lineweight]

1 hour ago, TonyT said:

I have my sink inch and a half connecting into my WC both connecting into the same 4”. The bath then connects to the 4” at the end of the pipe.

no probs

 

What height above the 4" is your bath outlet?

 

I guess what is in the back of my mind is the branch pipe blocking somewhere before it meets the vertical stack ... and then it backing up and unpleasant things appearing in the bath.

 

This scenario is avoided when the WC and the bath are on different branches, independently connected into the stack.

[Mr Punter]

I am pretty sketchy with plumbing so hopefully an all-knowing type will comment with a proper solution.  I will be interested to see.

 

With the top one you may need an AAV on top of the soil manifold.  Is it possible to take the bath / basin pipe out through the wall and connect it to the SVP?  The bath / basin run from looks quite long.

[lineweight]

...and if my second option is basically ok, does that mean that something like this would be ok:

 

If the main 100mm pipe were running *below* the floor (so 300mm or so lower down) then it would be different.... but when I look at this, it doesn't look right because the baths and the WCs all look too closely connected and asking for problems if there's a blockage.

 

Is there somewhere in the building regs or BS that specifically outlaws what I've drawn here?

Edited December 21, 2020 by lineweight

[lineweight]

1 minute ago, Mr Punter said:

I am pretty sketchy with plumbing so hopefully an all-knowing type will comment with a proper solution.  I will be interested to see.

 

With the top one you may need an AAV on top of the soil manifold.  Is it possible to take the bath / basin pipe out through the wall and connect it to the SVP?  The bath / basin run from looks quite long.

 

An AAV could be provided if necessary.

 

Yes, in theory the bath/basin pipe could go out through the wall independently, and in principle that would be better, but in reality it would get very complicated and messy to try and take two pipes through where they'd have to go. So this is what I'm really trying to avoid.

 

It would probably be less messy to drop them into the soil manifold, then down into the room below and then out through the wall there. But ideally, would want to avoid having to do that too.

[PeterW]

How long is all that ..??

 

Minimum distances for WC to stack are in the regs. 
 

Is this all first floor stuff ...?? Got a plan layout not section ..?

 

And is that drawn at 1:80..?? Last bath and basin want to be changed if you can but need to see plan layout. 

[lineweight]

It's all hovering around the 3m / 4m limits.

 

The plan arrangement is slightly in flux because the levels thing, and detail of the pipe exit through the wall is what is critical and what I want to try and pin down first.

[Temp]

I think I prefer your very first drawing with the manifold. However I would add a stub stack with AAV on the 110mm pipe on the right hand side near WC2.  Also allow room for a small AAV near basin 2 on their pipe.

 

Ideally instead of the manifold you would run two pipes through the wall to the stack where they would connect into it at different heights (thats in the Approved Doc) but if you can't do that then the manifolds should be ok.

 

 

 

[lineweight]

36 minutes ago, Temp said:

I think I prefer your very first drawing with the manifold.

 

 

 

Out of interest what would be your reason for preferring it?

 

Because I thought I preferred it but then once I'd drawn it out, I couldn't actually come up with a reason why it's any better than the second one.

[Temp]

 

9 minutes ago, lineweight said:

Out of interest what would be your reason for preferring it?

 

I can't see how your bath works otherwise.  Lets call the two pipes 110mm (WC) and 50mm (basin/bath). Even if the 110mm pipe is only just above floor level then the top connection into it for the 50mm pipe to the bath/basins would be something like 175-200mm above floor level. Too high for a bath?.

 

With the manifold approach the 110mm pipe for the WC can be raised up (if you use WC with horizontal outlet). That means the 50mm pipe can then run under the 110mm pipe at  floor level as per your drawing.

 

 

 

 

[lineweight]

1 hour ago, Temp said:

 

 

I can't see how your bath works otherwise.  Lets call the two pipes 110mm (WC) and 50mm (basin/bath). Even if the 110mm pipe is only just above floor level then the top connection into it for the 50mm pipe to the bath/basins would be something like 175-200mm above floor level. Too high for a bath?.

 

With the manifold approach the 110mm pipe for the WC can be raised up (if you use WC with horizontal outlet). That means the 50mm pipe can then run under the 110mm pipe at  floor level as per your drawing.

 

 

 

 

 

As I've shown it, the top of the 110mm pipe would be just about at floor level where the connection was made. That obviously wouldn't work in all cases - but in this case it could, because of the way the floor joists work. Then there is still enough height difference between there and the outlet level for a bath.

 

I've drawn it as if the connection goes vertically into the top of the pipe. But would it even have to? Approved Document H doesn't seem to have a lot to say about what should happen when one branch pipe joins into another. What it does say is:

 

 

That seems to allow for the possibility that the smaller pipe could simply join into the side of the 110mm one.

 

The soil manifold, I think, is mainly designed to deal with the Doc H requirements for what happens when a branch pipe connects into a stack. But that's not actually what I'm looking to do here.

[Gone West]

14 hours ago, lineweight said:

...and if my second option is basically ok, does that mean that something like this would be ok:

 

I can't see a real problem with that layout and it is the way I would do it as long as the drop is ok.