Getting it right: Bathroom shower & sink waste piping

Hi. I'm putting in a shower and re-positioning the hand-wash sink in the bathroom.

I'd prefer the fall/down pipe (the vertical run) to run down the inside of an external wall, then about 1 foot above the ground go through the wall to eventually discharge into a drain just below where it comes out of the wall on the outside.

I attach a picture of what I currently envisage. If we pretend for a moment that I'm not installing a shower, the drainage would only be for the hand sink. I believe I could use 32mm pipe all the way from the sink to the discharge point above the outside drain. You see that the slope of the pipe under the floor boards from the sink to the fall/down pipe is 9.84% Because the rise is 130mm over a distance of 1320mm. The only problem could be that the slope is too great. Perhaps someone could comment on this.

Okay, but of course I am putting in a shower. Now, in this drawing I show the shower drainage feeding into the main pipe, the one with a slope of 9.84%. If that was constructed, to the left of that junction, the piping may have to be larger. I say may because it in unlikely that the sink would be used whilst the shower is in use. And if that is the case one wonders whether the whole of the piping could be 32mm dia. Perhaps someone could comment on this.

In order for the shower to drain properly, there must be a drop in height between the pipe connection-point of the shower tray waste fitting and the point at which the shower waste piping meets the main waste pipe (i.e. the pipe sloping at 9.84%). That drop looks to be about 5cm (If the shower drain pipe connects to the main pipe at a right angle). The run for the shower drainage piping would be about 26cm. I suppose in theory that is alright, in terms of slope. But whether in practical terms things are alright could be a different story. For instance, would water from the sink start flowing up and out from the shower tray waste with the arrangement as described?

A question I have is: For what distance could a pipe be run horizontally from the shower tray waste fitting. The tray waste fitting I have has a pipe section that runs 7cm in the horizontal, then takes a 45 degree turn. Could that horizontal stretch be as long as 18cm?

Would it be much better to keep the pipes for the sink and shower separate until say they meet at a single vertical fall/drop pipe?

Thanks.

1. I'm not aware that there's any issue with too great a fall for waste pipes, only soil pipes/underground drainage where you have 'solids' featuring. I'm sure it's fine.
2. You need to be 40mm for shower, 32mm at any point is asking for trouble
3. I've done plenty of showers which do a straight run out of the trap across several meters with a very slight fall, so I can't see what you're worried about, your proposal sounds fine to me (apart from using 32mm for the shower)
4. I don't think there's a need to separate basin from shower, but a bath definitely wants a separate connection to the stack as it will empty the shower trap when you pull the plug out.

I have just posted a thread and noticed your own query. Some 17 + years ago I did exactly in two ensuites what you are proposing, the only difference was that I had the Y (well 45degree) join facing the other way so both discharges went in the same direction (imagine a sliproad joining the motorway). I have 32 mm pipe from basin joining into 40mm joint that takes the shower discharge pipe 40mm and at the bottom of the Y the pipe runs away in 40mm. Two teenage lads gave it a right test for 10+ years, never had a problem from fitting to now.

Off the topic of waste piping: I aim to install a 700mm x 700mm shower tray, it's made by MX and it is part of a line called "Elements". I think it's also DucoStone. It's very lightweight and it has to be laid upon a layer of cement. I suppose it won't take much flexing of the sub-base for the tray to crack.

I've put in an 18mm thick plywood sub-base. And it's supported on it's periphery. The arrangement at the moment is per the picture.

Is the support satisfactory as it is? Or is there a need for noggins crosswise of the joist which would make a kind of cross arrangement. Thanks.

EDIT: I suppose I could add the noggins, just to be doubly sure.that the plywood won't flex.

I think I will have two separate waste pipes, one for the shower, one for the sink. On the drawings I have made (See below), is there anything missing? Thanks. There will be the usual trap just below the hand basin. Just a hair trap in the shower waste fitting. Hope this suffices and no fumes get through into the house.

Nothing wrong with your drawings, and keep them separate if you can. Why the 300mm air gap to the gully? Ideally you want the waste terminating below the gully grating but still above the water line of the gully trap.

Around 45mm per m fall is the ideal, max 90mm, too much horizontal fall on the waste pipework can create self syphoning/gurgling at the trap.

Your support looks fine but extra dwangs for belt and braces is never a bad idea

Madrab said:

Nothing wrong with your drawings, and keep them separate if you can. Why the 300mm air gap to the gully? Ideally you want the waste terminating below the gully grating but still above the water line of the gully trap.

Around 45mm per m fall is the ideal, max 90mm, too much horizontal fall on the waste pipework can create self syphoning/gurgling at the trap.

Your support looks fine but extra dwangs for belt and braces is never a bad idea

Click to expand...

Hi. Okay I feel confident now I'll be doing right having had my plans looked at. That 300mm really should have indicated the height above the gully where the pipe comes out of the wall. I will make sure the end of the waste pipe is much closer to the gully (by gully I presume you mean the drain), about say 3cm above it. I will also take steps to support the longer hand basin / sink waste pipe. I am also minded to use solvent weld components except the first bend at the shower waste trap.

I don't want any fumes from the drain being smelt at the shower waste outlet in the shower.

DIYalot said:

by gully I presume you mean the drain

Click to expand...

Yup, your outside drain should be a gully trap, if not then you don't want to be using it. Fit a high quality shower drain/trap and ensure it has the largest seal that you can fit underneath the tray and clean it regularly then you shouldn't have any issues.

Okay let's just cycle through this: The drain at my house was built to take the waste from the downstairs and upstairs sinks. And also bathwater. I think there was a trap underneath the bath, and the waste water entered a hopper on the outside. The hopper of course discharged into the drain.The upstairs sink (has a trap) also discharged into that hopper. The downstairs sink (has a trap) just emptied into the drain. There is a metal grill covering the drain. This filters rubbish from getting into the drain.

Now, the only thing I know about my drain is that is goes down about 3 feet. Near the bottom there is a hole on the side, I know that because in the past it's got blocked up and it had to be unblocked. When I look down the drain I see that there is water sitting at the bottom.

I cannot say whether my drain is a gully trap. I can find out. I suppose it would be, because it has been fitted (1958) to take waste water.

Question:Is the shower waste fitting that collect hair also a trap to stop fumes getting into the shower?

The hole you are seeing 2/3rds of the way down would usually be the rodding access. There should be a water seal in the bottom of the drain and a u bend to ensure that sewer gases don't travel back up through the drain. Can you clean out the drain and put your hand all the way down and feel a U bend at the bottom?

Today I went shopping for the fittings to fit the shower and hand basin waste system. I've gone for the solvent weld stuff. Now, although not at this time fitting a bath I am wanting to put in (partly) the waste for a bath. Now, should the bath waste be 50mm diameter? And if it should, I cannot understand why I cannot source 50mm solvent weld at the place I've got the 32mm & 40mm pipe.

Doesn't have to be, no less than 40mm though. If it's a shared run then ideally you would increase to 50mm. 50mm is available at any good plumbing factors.

My experience with purchasing at a "shed" illustrates a problem regular DIYers have with these establishments. The store attendant did not understand his products. And of course, they are missing quite a lot of stuff. Did not appreciate that.

I have another issue: I'm going to surround the shower tray on two sides with a boundary about 100mm high. This is the shower curb. This will contain the shower tray sitting on a layer of cement that needs to be put beneath the shower tray for it to sit on. Currently my intention is to make this boundary from 18mm thick quality marine plywood. That will leave 50mm between the top of the tray and the top of the boundary, that height will be employed along with a shower curtain to prevent water splashing beyond the tray. But, is my choice of marine plywood for the boundary good? Thanks.

EDIT: No response yet, but I think even marine plywood is discouraged.

Is that 'boundary' on the outside of the tray? I.e. you would be stepping over that to enter the tray?