New soil stack needed or not?

[mike42]

We would like to add a new bathroom including WC. The main house already has two internal stacks serving two bathrooms. Am I right in thinking it would not be permissible to route a new 4 inch branch into one of the existing soil stacks because to do so would mean putting in a near 90 degree vertical elbow?

I'm really struggling to figure out the best route or whether I need a new stack even though the new WC is only about 500mm from an existing internal stack!

Any help/pointers most gratefully received.

 

[John D v2.0]

what's a 90 degree vertical elbow? the stack should be vertical, therefore by definition the branch will be near enough horizontal. Then just connect to the WC.

the main thing to remember is your waste obeys all the normal rules of physics

 

[^woody^]

You can connect it to the existing stack, and depending on the actual layout may or may not need a stub stack and air-admittance valve

 

[mike42]

Thanks a lot for the replies. What I meant by a "vertical 90 degree elbow" was if the branch needs to go vertical at some point to go through a floor/roof and you put a 92 degree elbow at the bottom then I'm assuming thats not allowed? Ahhh so maybe a substack would allow such a vertical drop as long as its within the dimensions in Part H ? Although this is at first floor.

Anyway, I've attached the layout of the 1st floor. Its essentially an L-shaped house with a 1st floor flat roof outside. The pic shows the proposed new WC at the top and two existing full stacks. Underneath the flat roof shown is just a gap between the original house and garage so ideal for routing ugly pipes. Maybe I should take a picture of that area as well?

Thanks so much for your time.

 

[John D v2.0]

Elbow is not allowed at the bottom of any stack, although you might get away with it.
Anyway I thought the point was you wanted to go into an existing stack, in which case you don't need to worry about the bottom of any new stack.

 

[mike42]

Elbow is not allowed at the bottom of any stack, although you might get away with it.
Anyway I thought the point was you wanted to go into an existing stack, in which case you don't need to worry about the bottom of any new stack.

Thanks John.

I was thinking that to take the outlet of the new WC (and shower + sink) I was thinking I could run it out as a horizantal branch outside along the roof next to the wall. That would connect into a vertical pipe (a stubstack I think?) . The substack would be located on the outside wall next to the existing stack (brown box at the bottom of attached pdf). The stubstack would drop through the flat room into the space below where a 92 elbow would connect into the existing stack.

Another option I could see would be to locate the stubstack just outside the proposed WC and then do the horizantal run internally at ceiling height. Really not sure which is better or if there is another way?

Since the substack would be less than a metre, I was hoping such an elbow going through the wall would be ok?

 

[John D v2.0]

Don't over complicate it, and certainly don't make any new holes in a roof! Just take it in at the same height as the existing. Use obtuse bends where possible.

 

[mike42]

How did you know I have a bad habit over never over complicating !

If the existing two stacks didn't already have WCs at first floor level, then I think it would be a much easier job as could take in at same level as you say. As it is I think I'd need to go in below the existing branches on the main stack. That either means going through the 1st floor roof or taking internally and being visible on the floor upstairs plus ceiling downstairs.

The flat roof is actually a terrace so very accessible so not sure if that chances anything?

 

[John D v2.0]

roofs are guaranteed to leak if you don't know what you're doing. If you can't connect in horizontally due to other branches, and you can't connect in to the other branch before it hits the main stack, then you'll have to drop it down, but boxed in inside would still be better than holing an existing roof.
Also try to make your stack combination point a Y branch with 45 degree, rather than putting in two right angles.

 

[mike42]

Right, I've think I've gone from trying to design the plumbing for the pentagon (!) to something much simpler - if its allowed. I hadn't thought of teeing into an existing branch. There is an existing branch running inside parallel to the wall. If I came in through the wall it would need I think two 90degree turns (one elbow outside with rodding eye and then the branch connector inside on the branch).

I think the relevant paragraph from the Regs is "1.17 Junctions on branch pipes of about the same diameter should be made with a sweep of 25mm or at 45degrees......." I'm hoping that the branch connectors at 110mm have radius considerably more than 25mm so I might get away with it?

Also is something like this preferable to use flat since it seems to have a sweep on it? Thing that worries me a bit is that isn't that normally used underground?
https://www.jtmplumbing.co.uk/pipe-...741/jtm-92-triple-socket-branch-p23353/s31436

The "above ground" ranges tend to have a sharper drop angle and look more for connecting to a stack? (e.g. https://www.screwfix.com/p/floplast-sp190g-92-5-branch-grey-110mm/12454)

Thanks again for your help - I think you might have already saved me a ton of work!

 

[seasickstevie]

I think you'll find they're the same.

 

[John D v2.0]

Both of those branches are fine, you won't find an unswept bend on a 110mm pipe. Since the dimeter is the same you can enter from the side but whatever you do make sure it doesn't enter from below horizontal. Normal rules of physics and all that.
You have a lot of choices of push fit and solvent weld, and it can be a double or triple socket connector, make sure you choice the right one.

I spent far too long thinking about soil pipes and ii stil ended up with a box full of spare parts where i bought the wrong stuff

 

[mike42]

Lol - I've also been spending a lot of time thinking about soil pipes when perhaps I should be doing something more "enjoyable" on a Friday evening. Anyway, I think I'm nearly there thanks to your help but one last obstacle is the existing branch into the stack was originally a solvent weld fitting (as per the pic in the link below). Following advice there I cut the connector and used a pan connector which had a rubber finned end that slotted into the stack. It worked well and looks and behaves a lot better than what was originally there.

However, that means I've now got a partially sawn off connector that I need to add my branch pipe to. I'm thinking it would just be a case of solvent welding a new pit of pipe but not sure. Perhaps I should take a picture of it how it currently looks? I'll try and get that shortly...

https://www.diynot.com/diy/threads/putting-wc-on-a-pedestal.499312/

 

[John D v2.0]

yeah solvent weld will connect to any 110mm pipe although you need a massive brush to get it all on in time before it evaporates
push fit is also fine but you have to mess arround chamfering a bit more, and it needs more depth of plain pipe, but at least it's adjustable later if you need.

 

[mike42]

Yes good tip re brush size. I guess I'm worried about whether this socket will still accept a new 110mm pipe after some of it has been sawn off. I've attached some pics. Note I do intend to move the WC a little to the right to give me more space to take the new branch coming in through the wall.