How long should a shower drain pipe be?

I installed a subfloor in my bathroom. I will be putting in a fiberglass shower pan. The shower drain pipe is below the subfloor. I was told it should be above the subfloor about 1/4 inches high. If this is correct can I unscrew the galvanized pipe from the the p-trap and use pvc pipe with a threaded pvc male adapter screwed into the p-trap and the pvc pipe glued into the adapter? being that the old shower pipe is old and rusty I would expect it to give me trouble trying to unscrew it..

 

All depends on the height of your pan and the type of drain you're putting in it. It's typically best to leave the stub out until the pan is temporarily set in place, the drain is in hand and you can actually measure how long it needs to be.

 

Yes..... I would expect it to give you trouble too.... such that you aren't going to be able to get it off without more access. Hopefully you haven't fastened the sub floor down yet. If you can't get it loose you may need to use a Fernco coupler and attach a piece of PVC that way. Allow several inches above the sub floor. You can always cut it later with a little rotary saw from the inside.

 

No the subfloor is not fasten.It can be removed for better access. If I can't unscrew the pipe I guess I will have to cut the pipe and put on a fernco coupling. any hints on unscrewing the pipe? I know I will be use a lot of penetrating oil and probably heat.

 

A b-i-g pipe wrench.

 

You've got galvanized drain piping. It has a limited life so I replace it with PVC whenever I have it exposed. Usually the bottom of the horizontal pipe sections rust through first. I would pull up the subfloor and replace the galvanized as far as you can do reasonably easy. It can save you (or someone else) from having to rip apart the bathroom to replace a leaking pipe.

 

I am going to reply here because what Dane mentioned is really important!

Your galvanized piping is likely past its useful life already. Installing a new shower into it is just asking for trouble down the road. This is a perfect time to replace as much of the galvanized pipe with PVC as you can. Replace it with PVC and use a no-hub coupling or a male threaded fitting to connect back to the cast iron stack or to the cut galvanized.

I would absolutely replace the trap and riser at the absolute minimum.

 

I was able to remove the drain pipe. I see a few has posted that I should change as much galvanized pipe that I can. It's possible I can change the piping up to the wall If I probably remove one of the planks from the subfloor. I was checking and I see the right joist I am able to get to but the left joist is under the wall. I am trying to figure out when I replace the subfloor, I can fasten down the right side but not sure what to fasten the left side to for support.

 

If the stud on the left is totally under the wall I would cut the old floor boards off flush with the wall. Then you can attach a piece of wood to the side of the existing stud as a nailer and support for your new subflooring.

While you are digging around under the floor measure the height of the floor joists to see how much room you have for the trap. Then measure traps available off the shelf in your area to see if they will fit, if not you may need to order something that will fit.

 

I am not sure how long the drain pipe should be for the shower pan. I read cut it level with the subfloor and I also read to cut it 1/4 to a inch above subfloor.

 

Combined threads.

Were you hoping for a different answer.

 

Don't install the vertical riser for the shower until you know what you are doing for the drain. That will tell you how high it should be.

 

Combined threads.

"Were you hoping for a different answer. "

Sorry for the double post. Been so busy I forgot I had ask this question before.