I’m preparing to finish my basement. This is a 2008 house with drain plumbing already built in to the existing concrete to support a bathroom.

Assuming tub/shower drains are in specific locations, how do you frame out a bathroom so that when it comes time to install the tub/shower it aligns with the existing drain pipes? The pipes stick straight up out of the concrete floor about 2 feet. Is a subfloor required? I don’t want to hack these babies off and find out I did something wrong.

What is the standard procedure here?

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  • Can you get us some pictures? Or drawing with room dimensions and pipe locations
    – Kris
    Mar 15, 2021 at 23:12
  • @Kris pictures added. Thanks. I don’t have measurements yet. Mar 15, 2021 at 23:16
  • 3
    cut outlines of the fixtures out of cardboard and place on the floor ... that will make it easier to visualize the layout and what changes need to be done
    – jsotola
    Mar 15, 2021 at 23:43
  • Are you thinking the layout is from brick wall. 1- tub shower. 2-toilet 3- vanity sink? With the vanity pipe coming up inside of stud wall?
    – Kris
    Mar 16, 2021 at 0:26
  • 1
    @kris yes. The toilet drain is 13” on center from the finished wall. The tub drain is 3.5” on center from the finished wall and 13” on center from the brick side finished wall. Seems like they may have placed things according to some forethought. Mar 16, 2021 at 1:18

1 Answer 1


Depends how it was installed. In many cases, the "standard procedure" is to cut the concrete open so you can get the "roughed in" (i.e. roughly positioned) pipes connected to exactly where you want them. Depending exactly WHAT was roughed in, you might need to do that so there IS a trap on the shower, for instance. The roughed in pipe may not have one installed, and unless you are raising the floor the shower/tub trap has to be under the floor level.

Concrete can be cut, drilled, and broken up as and when needed.

If you open the pipe up and carefully (don't drop anything in) shine a light down there, then pour a quart of water down the presumed shower/tub pipe, you should either see standing water (and the smell will stop) or you won't, and it won't. That will tell you about the trap situation. It probably won't have a trap full of water if it's been roughed in a while, even if there is a trap, so you need to add the water and see if some stays, or not. The toilet and sink/lavatory drains would not have underfloor traps.

If you do have a trap on the shower/tub drain, then you would need to choose the specific shower/tub you are going to use based on where it is, and how you will construct the walls, remembering the thickness of all layers, and build to suit - or cut the floor and adjust anyway.

  • Great informations I can’t imagine they wouldn’t have built in traps of they went so far as to install the plumbing for a bathroom. But I guess I’ll have to cut the caps off and check. I added pictures to my post. Tearing up the original concrete is more work than I want to do, and it is such nice work already. Mar 15, 2021 at 23:18
  • You'd be cutting a small hole around and next to the pipe, if there is no trap. The patch will be hidden by the shower/tub, unless you go utterly crazy. Just try to work with the toilet where it is, the other two are much easier to move slightly (sink drain adjustments above the slab, normally.)
    – Ecnerwal
    Mar 15, 2021 at 23:22
  • Assuming there is a trap and I don’t tear up the concrete, is there a technique for aligning all my framing to match up with a drain on a tub/shower? Seems like a weird problem. Mar 15, 2021 at 23:36
  • Measure and mark, just like building anything else that has to match up. It's painful and fiddly work any way you do it, which is why there so much money to be saved (in skilled labor not hired) by DIY-ing a bathroom. Of course, the skilled labor (hopefully) comes with skills and experience, which is why they are expensive. Use a sharpie and check the measurements 3 times before fastening the framing.
    – Ecnerwal
    Mar 15, 2021 at 23:40
  • This vid shows how a drain attaché to the stub up. google.com/…
    – Kris
    Mar 15, 2021 at 23:58

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