Shower waste trap and P bend

[Madrab]

I won't be emptying the bath, draining the sink and having a shower at the same time so thought I'd just do 40 the whole way.

The ideal would be that each outlet has it's own run to the stack, this eliminates any traps being pulled when another outlet is discharging. Where that's not possible then where it tees to a downstream outlet - increase the pipe size to the next size up to the max of 50mm. It is a standard practice to ensure it minimises syphoning effects on all the traps on the run. Try and run each outlet on it's own waste pipe as far as possible to the stack before it tee's into the shared run and make sure any swept tee is fitted in the right direction. I know it sounds obvious but you;d be surprised how may are fitted the wrong way

Also use an anti vac trap on the bath and basin - ensures the run in well ventilated and reduces the risk of the bath water pulling on the shower/basin trap.

Essential to get at least the min fall of 25mm/m on the shower waste, if not there can be issues with correct drainage as the head of water is low.

That shower waste does look like it has a water seal/dip tube setup, if so then no need for a downstream trap

 

[AverageDIYerEssex]

The ideal would be that each outlet has it's own run to the stack, this eliminates any traps being pulled when another outlet is discharging. Where that's not possible then where it tees to a downstream outlet - increase the pipe size to the next size up to the max of 50mm. It is a standard practice to ensure it minimises syphoning effects on all the traps on the run. Try and run each outlet on it's own waste pipe as far as possible to the stack before it tee's into the shared run and make sure any swept tee is fitted in the right direction. I know it sounds obvious but you;d be surprised how may are fitted the wrong way

Also use an anti vac trap on the bath and basin - ensures the run in well ventilated and reduces the risk of the bath water pulling on the shower/basin trap.

Essential to get at least the min fall of 25mm/m on the shower waste, if not there can be issues with correct drainage as the head of water is low.

That shower waste does look like it has a water seal/dip tube setup, if so then no need for a downstream trap

Read this about ten times to try and digest it. So annoying when you think you have a plan and then find out it's wrong. Or at least can be done better. lol.

So this is a rough diagram of the setup with my original plan. The red lines are the joists (which can and do have holes in) I will probably have to reimagine it now so that they all run as far on their own pipe as possible. Thought I had all this worked out. But then that's what these forums are for right. For helpful people to share advice so thank you for that.

Isn't the minimum fall 18mm in 1m I thought I read? I was working out using 20mm.

However I think it would be better to run each pipe further down... one sec... getting my pen out.

 

[AverageDIYerEssex]

So would this be better if I can achieve it? I'm thinking 40mm from the utilities downwards and then the horizontal pipe going into the boss being 50mm. Would that work?

This way the holes in the joists will be further from the edge of the house which I'd prefer.

 

[Madrab]

Isn't the minimum fall 18mm in 1m I thought I read? I was working out using 20mm.

As far as the regs are concerned - then yes min fall is 18mm/M - but that's just to ensure there is enough fall in the pipework to empty properly under gravity and allow enough water velocity to reduce the chance of anything suspended in the water from dropping out and clogging the pipe. This though is more relevant to outlets that have a reasonable head of draining water - basins/baths etc that tend to be at a greater height

When it comes to a client looking for a nice new and modern low level tray with high output shower then that's a whole different ball game. Even with the min fall, certain traps and trays have trouble draining fast enough to cope with high flow showers and lots of soap/bubbles as they can suffer from airlocking. I always work to a min of 25mm/M with an ideal of 45mm plus per M. The greater the fall the faster the tray and trap will drain and also allow for a self cleaning waste run.

So would this be better if I can achieve it? I'm thinking 40mm from the utilities downwards and then the horizontal pipe going into the boss being 50mm. Would that work?

Yes - as a shared waste run that would be ideal.

 

[AverageDIYerEssex]

As far as the regs are concerned - then yes min fall is 18mm/M - but that's just to ensure there is enough fall in the pipework to empty properly under gravity and allow enough water velocity to reduce the chance of anything suspended in the water from dropping out and clogging the pipe. This though is more relevant to outlets that have a reasonable head of draining water - basins/baths etc that tend to be at a greater height

When it comes to a client looking for a nice new and modern low level tray with high output shower then that's a whole different ball game. Even with the min fall, certain traps and trays have trouble draining fast enough to cope with high flow showers and lots of soap/bubbles as they can suffer from airlocking. I always work to a min of 25mm/M with an ideal of 45mm plus per M. The greater the fall the faster the tray and trap will drain and also allow for a self cleaning waste run.


Yes - as a shared waste run that would be ideal.

Right. I think I'll be able to get a bigger fall if I run it that way. I'll have a look tonight. Hopefully no more water pipes need to be moved. Thanks for the help. Would you mind if I uploaded a picture of what I was thinking in relation to the boss setup when I get the chance to take it?

 

[Madrab]

Would you mind if I uploaded a picture of what I was thinking in relation to the boss setup when I get the chance to take it?

Not an issue at all

 

[AverageDIYerEssex]

Not an issue at all

Ok so image 1 is what I put in for the upstairs toilet. I fitted a boss to run the upstairs services too. However it is only in the middle of the joists.

Image 2 is another position further along (2.5cm lower than the first, but also a bit further along so will need extra drop to get to) the strap boss isn't fitted and is only for testing, I have a solder weld boss to go in the final position

Image 3 is another possible position for the new boss and would give a greater fall, but again a bit further of a run.

I'm going to draw out some examples of what in my mind might work and hopefully you can see what you think.

 

[AverageDIYerEssex]

 

[Hugh Jaleak]

I would seriously avoid putting the bath and shower on the same run if at all possible. Got called to a job once, Young Couple, their first home. She'd been on a long night shift as a Neo Natal Nurse, driven home and gone for a long, well deserved soak in the bath. Pulled the plug and went into the bedroom to dress and grab a few hours much needed rest.

However, unbeknown to her, the waste pipe was blocked downstream, and as the water began to drain from the bath, it couldn't get away and found its own level, exiting via the shower tray. By the time she realised what was going on, the upstairs carpets were sodden and water was pouring through the kitchen ceiling below.

 

[AverageDIYerEssex]

I would seriously avoid putting the bath and shower on the same run if at all possible. Got called to a job once, Young Couple, their first home. She'd been on a long night shift as a Neo Natal Nurse, driven home and gone for a long, well deserved soak in the bath. Pulled the plug and went into the bedroom to dress and grab a few hours much needed rest.

However, unbeknown to her, the waste pipe was blocked downstream, and as the water began to drain from the bath, it couldn't get away and found its own level, exiting via the shower tray. By the time she realised what was going on, the upstairs carpets were sodden and water was pouring through the kitchen ceiling below.

Ohhhhhh yeah. That's a good point. I suppose because the head height of the bath and the basin will be above the shower tray it will find its level somewhere in the middle = all over the floor and carpet. That's a good point.

So do you think drawing 1 would be better?

 

[Madrab]

yeah +1, as suggested - ideally on their own runs but certainly not shared with the bath, given the volume of water and the height difference.

If we're going by the regs then :-

Diag 1 shower run exceeds the max length by 1500mm. You could get away with it if it's upped to 50mm with a 45mm/m fall but even then, by the regs, it would be 500mm too long but I'm sure there wouldn't be an issue with the proper fall
Diag 2 does fall within the criteria but as suggested you really want to avoid having the shower on the same run as the bath. You could add another boss in just after the 1st one to take the shower on it's own, keeping the runs shorter.

 

[AverageDIYerEssex]

diag 2 does fall within the criteria but as suggested you really want to avoid having the shower on the same run as the bath. You could add another boss in just after the 1st one to take the shower on it's own, keeping the runs shorter.

This is probably what I will do then. I'm off work Wednesday so going to measure and work out how much fall I can get away with.

What are your thoughts on the strap on vs solvent weld bosses? (I know the strap on's are SW also but you know the other one I mean, the big ones with 3 potential inputs)

 

[Madrab]

The boss branches are obviously good as far as a permanent part of the pipe but as long as the strap on boss is fitted and fixed properly then it's just as good for a single inlet.

 

[AverageDIYerEssex]

Brilliant thank you. As you can see I've not got too much space to play with and would be a LOT easier to use a strap-on.

Orrrr... do you think it's worth replacing this upward elbow...

With one of these (obviously the sweep going up ready to connect to the toilet above)

And then one of these in the front end for the bath/sink run?

or I could probably get a double inlet one and run 40 from the sink and 40 from the bath independently.

The shower can then go onto the SW boss that's already on that pipe.

I really do appreciate your time and advice btw. Thank you.

 

[Madrab]

Nope - I can see where you are coming from but that's primarily designed for a vertical stack, especially push fit.

Is the other soil/waste pipe and fittings Aquaflow from TS? I have found their sizes to be a little out for compatibility with the other standard pipe and fittings available especially their waste pipe and fittings.