Shower drain relocation

[ndjur]

My second storey bathroom is above the dining room, and in order to make room for plumbing, the dining room ceiling is dropped 10” below the joists, which creates 20” high spacing between the dining room ceiling and 2nd storey bathroom floor. It’s a 40 year old townhouse with well functioning wet venting (so far). I attached

In order to install linear shower drain against the side shower wall, I would like to move the drain about 22” away from its current location. However, this will put the drain above the 1st floor living room, where I only have 10” height – the height of the ceiling joists. I can see two solutions to this problem, both probably being more or less wrong.

One is to leave the current shower P-trap where it is and to run properly sloped pipe from the new drain location to the existing P-trap. This is probably better out of these two solutions.

The second one would be to relocate the P-trap under the new drain (inside 10” joist spacing) and run a new 2” drain pipe to the main 3” drain/vent pipe. However, in order to do this I would have to create a steep slope, coming from the joist spacing, above the beam and into the current piping.

Maybe there is one more possibility – to move the P-Trap and to add another vent pipe before the big slope into the piping spacing, but this new vent would have to run horizontally to the side wall before it goes up, and I’m not sure if makes sense.

I hope these drawings and pictures will explain the situation better than my long description. Pictures were taken during ceiling replacement.

Thank you in advance for all suggestions.

Nick

 

[BMWpowere36m3]

You have to vent the trap arm before it drops vertically... so option 3 looks good. Put a p-trap under the linear drain, slope the 2" line 1/4 per ft. towards the original waste line (between joists), put in a wye for the vent, continue the 2" waste line and install a 90 deg elbow and drop into the original waste line.

Anything greater than 45 degrees is considered vertical and the vent must remain vertical till it is 6" higher than the flood rim of the fixtures its connected to.

 

[Sponsor]

 

[ndjur]

Thanks a lot E36 for such a prompt reply.
I don't know if I was even correct in listing the option 3, as it may not be doable. The issue is that the new vent line would have to go horizontally below the shower, through the joist 2 and joist 1 and only then it can go 90 degrees up behind the shower wall into the attic where it would connect to the existing vent line. However, this shower wall is also a party wall between two townhouses and I'm not sure if I could or should do the drilling through it.
Also, would the vent line that first runs about 20" horizontally do its job? The horizontal portion would fill up with water quickly, wouldn't it?

 

[BMWpowere36m3]

The vent cannot be horizontal till its 6" above the flood rim or 42" off the floor.

 

[Terry]

You can leave the trap where it is and 90 over to the new location.

Or if you relocate the trap, make sure you add a vent before it dips down.

 

[ndjur]

Thanks a lot for your suggestions. Although I understand that adding the additional vent to relocated P-trap would be ideal solution, due to the layout of the whole system I'll leave the trap where it is and add a 2" properly sloped pipe to the new location.
Now when my drawings are there, I will just use the opportunity to ask if you see any problem in replacing the standard toilet with the wall mount one. Obviously, I have to make a small relocation of the toilet drain pipe, but would anything else change due to the higher toilet drain location?

 

[hj]

quote; However, this shower wall is also a party wall between two townhouses

It is usually not only a party wall, but a "fire wall" as well and you CANNOT cut into it without restoring its fire rating, (and anything you put inside it would also have to "fire proof" meaning NO plastic materials).