Do I need to relocate the shower and open the floor again if I rotate by basement bathtub 90 degree around the drain point?

Question

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 and here is the new layout

Answer 1

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.

2. 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.

^{Picture Source}

3. 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.

Answer 2

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.

Answer 3

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...