Hi,

Looking for some advice on plumbing the drain on a Schluter-Kerdi shower system. I am a pretty confident DIY’er, but almost contracted this out until I found these great web sites! I am replacing an existing 3’x5’ tub with an already purchased Schluter-Kerdi system (which requires the Kerdi-drain moved to the middle of the space). There were two tubs on the second floor sharing a wall; so all the existing plumbing handles both tubs. If you look at the two attached pictures, I hope you can see my problem. In [View #1] you can see the removed sub-floor. The joists are only 2”x8” (giving a clearance of only 7”) and the Kerdi-drain needs to go right over the corner of the exterior wall below (which shouldn’t be cut). I have just enough room to put the Kerdi-drain, but the trap is going to be a problem. If I can put in a 90 elbow and move the trap out about a foot then I have space. I know the trap “should” be right under the drain and normally I would; however, is there any allowance when you can’t do this that will pass an inspection?

Any suggestions are really welcome.

My second problem is tapping into the existing DWV system. The nice thing is that I have access to a 2” ABS drain. My thinking is to actually re-plumb the existing tub drains (see View #2). Drain [A] is the tub that stays, drain [B] will go. One possibility is to re-plumb the 2” line to the double WYE, replacing the double WYE with a 2” double WYE and reduce only the vent (1.5”) and the tub that stays (1.5”). That way the shower gets a full 2” drain and ties into the vent about 2’ from the trap (as per my problem above). Also, will I have issues with drilling a 2+” hole in the 2x8” joists? I know I am pushing it if I drill the joists, but I have no ideas left on how to get the vent tied in.

One other possibility is since I am putting a bench in the shower, I can trim the Kerdi-tray equally on both ends--which will move the Kerdi-drain off the wall… probably just hitting the joist. I have seen postings indicating you shouldn’t cut the tray, but I have seen postings indicating that you can cut it if you do so evenly on both sides. It will still all be covered in Kerdi.

Once again, suggestions are really appreciated. I will be posting project progress as it moves forward, but I am stuck until I can get a little advice on how to plumb the drain and still pass code.

Thanks for a great resource.
Ted

Hi Ted and Happy Easter,
" If I can put in a 90 elbow and move the trap out about a foot then I have space. I know the trap “should” be right under the drain and normally I would; however, is there any allowance when you can’t do this that will pass an inspection?"

What you are proposing is called a "running trap" I can find no objection to this in my Standard Plumbing Code book, however, local codes might outlaw it. Check with your building department to be sure.


My second problem is tapping into the existing DWV system. The nice thing is that I have access to a 2” ABS drain. My thinking is to actually re-plumb the existing tub drains (see View #2). Drain [A] is the tub that stays, drain [B] will go. One possibility is to re-plumb the 2” line to the double WYE, replacing the double WYE with a 2” double WYE and reduce only the vent (1.5”) and the tub that stays (1.5”). That way the shower gets a full 2” drain and ties into the vent about 2’ from the trap (as per my problem above). Also, will I have issues with drilling a 2+” hole in the 2x8” joists? I know I am pushing it if I drill the joists, but I have no ideas left on how to get the vent tied in."

What's the difficulty with cutting out trap "B" and running over and pick up the shower from "B"'s drain line? Then vent stack "C" will be used for both the tub and the shower. Code lets us take a 33% cut or hole out of a floor joist or rafter. We use a angle drill and a Milwaukee 2 9/16" Self Tapping Wood Bit to drill holes for 2" PVC. Good luck on your remodel job. Tom