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In the picture below (current layout) the shower heads will be located in the corner on the exterior wall. As you can see in the new layout I would like to install a new bath tub but this time along the exterior wall AND keep the shower head and the water pipes/ and the tap in the same position/ Are there any pros and cons for this plan? Can I expect to have to open the floor again to reposition the drain IF the drain is off a couple of inches (2-3in)? Is there a solution to avoid that?

As you can guess I am trying to not to have to redo the plumbing

Here is the current layout enter image description here and here is the new layout enter image description here

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    When it comes o bathtub installs over concrete floors, there is always a section of floor that is not poured, so the overflow and waste can be better aligned over the J bend or P-trap. The trap is never set until the tub is known or on site to finalize the trap location precisely so the overflow and drain can be set up into that trap, so when the tub is set everything lines up to screw in the drain grate and overflow cover. When and if you relocate the tub, you will only need to redo the trap to accommodate the new tub drain location Getting the sink drains is another issue but doable I think.
    – Jack
    Jul 26, 2020 at 22:35
  • my current understanding is that I could run the sink drain along the wall and I could probably connect it to the drain of the tub or go all the way to the main drain (the vertical one
    – MiniMe
    Jul 26, 2020 at 22:42
  • Not IN the wall?
    – Jack
    Jul 26, 2020 at 23:05
  • yes along the wall line, in the wall
    – MiniMe
    Jul 26, 2020 at 23:07

3 Answers 3

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You will most certainly need to move the tub drain. That move may very well be more than just a inch or two. There are three issues I see here.

  1. Non-uniform dimensions. As in the diagram below the green dimension on a bath tub is typically longer than the red dimension. Then depending on the top side shelf widths the green dimension may very well likely not be centered on the tub overall width. This means that if you can rotate the tub ninety degrees the drain will not be possible to be the center of rotation.

enter image description here

  1. The second issue is that built in tubs have one side face that comes down to the floor. The tubs can be purchased with the drain hole on the left or right side when the side face of the tub is in front of you. If you intend to reuse the same tub you will end up having the drain on the opposite end that what you envision with a simple rotate. If you intend to replace with a new tub you will have to make sure to switch the leftness/rightness of the drain hole location with respect to the current tub. The picture below shows the right hand and left hand models of the same alcove style bathtub.

enter image description here

Picture Source

  1. From your pictures where you depict the toilet located on the second floor it seems very likely that there is plumbing coming down from the upper floor to the lower floor in that stub wall that is in the lower level bathroom. You will want to check this carefully before you finalize your plans so you can factor in what this may mean to your overall project.
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  • yes that seems to be the case, there is a pipe comming out of the roof on that vertical and to my disappointment in it probably aligned with the back side of the main floor toilet ...there is a small bump at the top side of that wall just below that upper floor toilet> Do I stand any chance to relocate that wall? The drain might be there and it could be extended with a vent...
    – MiniMe
    Jul 26, 2020 at 20:10
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The location where the tub drain is, typically has an area of the floor where the drain is that is not poured, so the p-trap can be adjusted the final amount for the connection to the tub. You most likely will need to cut out the old p-trap to configure the new one.

I am not certain of the code, but for one sink you can use 1 1/2" pipe for the drain, but since you have 2 sinks, you will need to run 2" pipe. That means drilling 2 1/2" to 2 5/8" holes through the 3 1/2" studs, not leaving much for strength. In addition, you will need to run a vent line to tie back in to the original as well. Vents are to be within 5' of a sink or tub. If the vent comes off the tub drain, you may be in luck, but if it come off the old sink location, it will need to be added. Back at the drilling, you cold notch the pipe, leaving 1" on one side and use a reinforcement piece that guards the pipe from fasteners and strengthens the notch.

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  • it will be one sink, I did not find the right sketchup object to represent that, it is a one piece top and sink (acrylic)
    – MiniMe
    Jul 26, 2020 at 16:00
  • The 2" hole will be much better then
    – Jack
    Jul 26, 2020 at 18:38
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You may have trouble with the drain positioning. The waste-and-overflow assembly is designed to tuck into the space at the head of the tub, created by the sloping end of the tub. To get to where the drain pipe in the floor is now, you will likely need to bend around the tub wall. So be prepared to get creative with one or more 45° fittings.

There is also the problem with it being a generally bad idea to mount the shower head such that it sprays out toward the room, but with a proper enclosure you should be fine. If this will be inspected by the AHJ (Authority Having Jurisdiction) you may want to open a dialog with her/him before you start...

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