New shower not draining - have some ideas but need help!

[mwebber]

Hi,

I've just installed a new shower tray and power shower (I'm a DIYer rather than professional!). I've not touched any of the existing pipework under the floorboards.

When the shower is working at it's maximum flow rate, the tray fills with water and takes a while to clear - essentially it seems that the existing pipework can't clear the water quick enough (the old shower was pathetic which is probably why I never had the same problem before). It seems stupid to just accept that I can't use my sparkly new shower on it's max power, so I'm trying to work out a solution...

The drop of the wast pipe seems acceptable - the total length of pipework under the floorboards is 3.8m and drops by 10cm (so approximately 25mm drop per metre of pipe). The pipework has to go around 2x 90 degree turns in the first metre of pipe, then runs straight out through the wall. Once outside the wall it does a 90 degree downward turn and joins into another 40mm pipe (along with the bath and sink wastes) for a metre or so into the stack (so essentially the water does 2 90 degree turns inside the house and 2 outside).

Any suggestions?! From scouring the forums all morning, I can see 2 possible was forward, but need some advice!

1) There is probably scope (with a lot of hassle) to drop the pipe inside the room by another 5cm or so. This would then place the shower waste pipe below the height of the existing exterior pipework so I'd need to run a new external waste pipe into the soil stack - this would allow me to create an even steeper drop off in the last stretch of pipe if that would help?

2) reduce number/ severity of the 90 degree bends. If I drop the pipe as suggested above, I could elimate one of the turns on the outside of the house by removing the 90 degree turn (i.e. set the pipe to enter directly into the exterior pipe rather than doing a downward turn first). I might also have scope to reduce the severity of two 90 degree turns under the floorboards.Is this likely to help, if so what sort of thing do I need to create a sweeping bend? flexible/concertina pipe?

Another thought, would I gain anything from splitting the flow into 2 pipes using a 45 degree branch tee to allow the water to flow away through 2 40mm pipes rather than just the one? because of the way the original pipework is cut through a joist, I couldn't insert such a split until after the first metre (where the 2 right angle turns are). Would I gain anything if the water still has to go through the first metre in a single pipe?

Help! I've been working on this bathroom project for over 2 months now and I thought the end was in sight!

Thanks!

 

[Nige F]

You thought there was light @ the end of the tunnel Is it possible to remove the shower waste connection into the other pipes Outside and run it on it`s own into the stack - leaving the inside alone . This is how it should be done yet even now on new build near me - the pipes are all joined up then run to the stack If you can re jig it you could also put a cleaning eye on the outside ... to clean it through A picture would help.

 

[Richard C]

25mm/m fall would be enough under normal circumstances but your current drainage arrangements are a bit of a disaster area by the sound of it. The total length for an unventilated, 40mm branch waste is 3m extending to 4m if you use 50mm waste (also a Building Regs requirement), anything above that & with the number of bends you currently have is bound to give flow rate problems when using a power shower. For power showers, I will only use 40mm for short straight runs directly into the stack otherwise its 50mm. Splitting the pipe with a branch tee will not really help & additional cutting of the floor joists for the waste pipe is a definite no, no & it should not have been cut originally. Teeing into the sink bath waste run is also a bad idea, you will continually siphon the water from the traps unless you fit air admittance valves or Hepvo traps, ideally each appliance should have a separate connection to the stack.

Somehow or another you need to get direct connections to the stack (at least for the shower) within regulation length requirements or provide ventilation; you also need as few bends as possible, each bend you put in will restrict flow rate.

 

[mwebber]

Aaargh! Thanks very much for your replies - don't be offended when I say that it really isn't what I wanted to hear! Still, if it needs fixing, it needs fixing...

Current drainage arrangements are indeed a disaster area (most of the previous work throughout the house has been done very poorly). You can see the first 2 joints (and the ENORMOUS chunks that have been hacked out of the joists which I've tried to bridge in order to support the floorboards) in this picture:
View media item 29705the pipe then continues straight along to the left and outside:
View media item 29706The shower waste is the middle one.

I've reused the existing pipework to avoid having to cut anything else into joists, and to enable me to reuse the original pipework in terms of where it exits out of the wall and into the stack etc. Is there anything that I can do 'make good' the existing set up?! Will fitting 'air admittance valves' do the trick on their own given the scale of the problem? On full power, the (slimline) shower tray is ready to overflow within 2 minutes! I could put one in the stretch of pipe that runs across the cut joist as this will be in the airing cupboard...

If not, I need to rethink the whole thing. I could, in theory, take a waste pipe direct from the shower trap and straight out through the wall (parallel to the existing pipe but on the other side of the joist), with it's own entry into the soil stack (although this won't be particularly aesthetically pleasing outside given that it will have to join the stack below the collar you can see in the photo...). The biggest problem with going down this route is that I would have to turn the trap around. It sounds like a small problem, but the tray is bedded on mortar and the trap is remarkably difficult to access to do anything more than check for drips due to the fact that it is butted right up next to a joist and has copper pipes running alongside! actually unscrewing it, re-siliconing it and turning it around would be, I think, VERY difficult...

So, where should I go from here??!!! (apart from to a dark room for a lie down! )

 

[Richard C]

If I were you I would get the aroma therapy going in that darkened room along with a Scottish Moors CD & a large glass of your favourite tipple & do some serious thinking.

If you were totally honest with yourself I think you are already aware of what you need to do as you’ve more or less answered your own question

If not, I need to rethink the whole thing. I could, in theory, take a waste pipe direct from the shower trap and straight out through the wall (parallel to the existing pipe but on the other side of the joist), with it's own entry into the soil stack (although this won't be particularly aesthetically pleasing outside given that it will have to join the stack below the collar you can see in the photo...).

I doubt there is anything you can do to make the current set up work satisfactorily; the pipe run is too long, too torturous a route & of insufficient size to cope with the sort of flow rate you now require with your power shower; although you don't say what the litre/min delivery rate is. I don’t think venting will make much if any difference either; you could try disconnecting the sink trap (below the trap so it’s open to air) to see if it makes any difference but I doubt it.

If the joist’s been like that for a while, the house probably isn’t going to fall down (not yet anyway) but those are seriously nasty notches. It’s not possible to say how much the joist strength has been compromised or if it’s of any real significance without knowing the joist span & where the support points are but it’s probably not helping with floor rigidity; got any cracked floor tiles in the bathroom?

The added bonus of biting the bullet & rerouting the shower waste in 50mm direct to the stack (with all that may entail) is that you can repair the damage that’s been inflicted to the joist & you will at least have a separate waste run from the bath/sink; there is no way a single 40mm stack connection can cope with all 3.

Either that or get used to 1 ¾ minute showers.

 

[mwebber]

Thanks again Richard. You read my mind! I have been sitting with a cold beer pressed against my forehead in contemplation (it seemed a little early in the day to hit the top shelf! although...)

I actually just came on to edit my post - I remembered the most important reason for not running the waste pipe straight out in the first place - there is a concrete hearth for an old fireplace and various supporting joists in the way at the end of the run, so the only way out is across the joist. Given the almighty chunk you've already seen is missing from the relevant joist (which is almost a third of the distance along it's length... terrifying indeed), I thought the best thing to do was to reuse the cut groove rather than cut anything else into it!

So... the only way I can go is the way it already is... No denying that this is bad news! On the up-side, even with the shower at half pressure (which doesn't overflow!) it's infinitely better than what we had before!

So, how can I make the best of a bad situation. My current plan is as follows
- switch out the 40mm waste for 50mm
- change the first 90 degree knuckle bend for a 90 degree swept bend
- change the second bend for 2x 45 degree turns spread as far apart as possible to reduce the severity of the turn
- increase the drop over the distance of the pipe
- take the 50mm pipe straight out of the wall and direct to the stack (i.e. not linked to the bath or sink)

How much is this likely to gain me?! I know it won't be perfect, but is it likely to make a noticeable difference? Shall I stick a vent in the airing cupboard for good measure?

Finally, the outlet from the shower trap is 40mm. Do I need to step this up to 50mm pipe immediately, or can I put in the 40mm-50mm adaptor say 25cm out from the trap?

Thank you so much for your help - reading the books tells me how it should be done in the first place, but not how to remedy someone else's mess! Picking the mind of a pro is immensely helpful!

 

[Hugh Jaleak]

Looking at the photo's I would be inclined to swap the 1st 90 elbow for a swept bend, then upgrade to 50mm on the 2nd 90. This should avoid hacking any more out of those joists! Might be worth looking at the shower trap too, high flow versions are available for power showers to allow the extra water to drain effectively.

Presume bottom section of the stack is iron? Could renew that in plastic to ground level where it joins the drain, then you have ability to fit a boss connection as necessary to accept the 50mm. Alternative would be to fit a 110mm manifold under the existing tee on the stack, then connect existing and proposed wastes into that. However, a manifold may not be the prettiest thing outside the house and there may be a risk of freezing in these colder months.