Which job is easier?

[mike42]

HI

So as part of an ongoing renovation I'm planning I think I've figured out that to connect the waste of a new shower I either need to:

A/ Connect into an existing 40mm elbow at ground level that dives into a concrete floor. I don't have much experience with waste but I think this is solvent weld so would need to cut off the existing elbow just above ground and then somehow expose enough pipe beneath the concrete so I can get a new tee on.

OR

B/ Come through the back of an exciting stack with a 40mm boss at around ceiling level. I'd need to first remove the existing plywood boxing and then make good. Again no experience of doing this hence asking here. Also not sure whether I could "boss in" at the same height as the existing connection that you can see. Going lower shouldn't be an issue either.

So which is best/easiest ? Thanks a lot for reading and esp if you have a view?

 

[flameport]

Option B.

A could easily go very wrong in several ways, particularly if you haven't dealt with such things before.

 

[Hugh Jaleak]

Using Option A may cause you to exceed the permissible length of waste (3m) allowed under regs, so B is really the only option.

 

[mike42]

Yes A was to the ground which would mean a lot more than 3M. Option B would be about 3M. This would be a dedicated shower waste pipe.

If doing option B, any thoughts on drilling a bit bigger than 40mm hole through a cavity wall then through the stack boss ? Maybe I'd have to cut away a section of stack, drill through the wall from the inside then fit a new 110mm connector on the stack?

 

[Hugh Jaleak]

Are you coming back through from outside with this waste? May be wise to look at any possible external options too.

Coming back to your point about 'bossing in at same height as the existing connection', horizontally opposed connections aren't allowed, to prevent crossflow, non opposed can be at any position. Might be worth you having a read of Part H of the building regs. All the info on what's allowed/not allowed is there. http://upload2.evocdn.co.uk/jhai/uploads/download/3_0_br-pdf-ad-h-2010.pdf

 

[mike42]

Got the point about opposing connections. Other angles are allowed but are they physically practical? i.e. if there is a boss already there?

I think both A and B would be longer than 3M so have been looking at the Part H link you kindly provided. I'm thinking now if I fit anti-syphon traps on both sinks and then have an upstand of 40mm pipe higher than the highest sink overflow (for the shower) and put an AAV on top of that, then that might work? In theory two sinks and one shower would be sharing the same branch.

If I did go down the option A route (with ventilation discharge branches as above), could I carefully cut off the existing connector to expose a lip of bare pipe and then push something like this into the pipe (with solvent glue)? :
https://www.screwfix.com/p/floplast-conversion-bends-90-white-40mm-5-pack/73715
But I guess I'd need a tee version of it and can find one of those.

 

[Hugh Jaleak]

You wont get a strap boss on if there is already a fitting at that level. Options are to drop is slightly lower or cut existing boss section out and fit a boss pipe in place, allowing a second connection. If you are going to exceed 3m, I'd look at upsizing to 50mm pipework after 3m.

Unless you can expose some more, clean, pipe downstairs to get a fitting onto, coupling on at the existing bend isn't viable. You would need to cut the fitting off, tight at the lip of the socket, then find sufficient clean pipe to get another fitting onto. It will need to go over the pipe not inside it.

 

[John D v2.0]

Just to clarify if it helps, the no connection zone caused by a branch into a stack doesn't include the situation where the swept bends go in exactly level with reach other. This is why you can get opposing swept stack entries.

 

[mike42]

Just to clarify if it helps, the no connection zone caused by a branch into a stack doesn't include the situation where the swept bends go in exactly level with reach other. This is why you can get opposing swept stack entries.

I did wonder why this kind of thing is available:
https://www.drainagepipe.co.uk/products/ring-seal-soil-pipe-system/92.5-double-branch-110mm-soil-/

Not sure I fully understand but I won't be using that anyway, although I will be using this right-angled version a bit higher up the stack which I think is allowed:
https://www.ebay.co.uk/itm/4-Soil-P...500778?hash=item1a0e71fbea:g:idAAAOSwjMJXB7Ct
My 40mm (and now probably 50mm based on your advice) will be going in a little lower down).


Anyway, it looks like I will go for plan B (into the existing soil stack). Digging out concrete to expose more pipe without damaging it sounds very hard. I also now realise my stupidity thinking a street elbow might be the solution - the "street" part just means it can be treated like pipe and go into a fitting (but not another pipe!).

Thanks a lot for your help Hugh.