Replacing old tub with shower base. Drain ends up on joist. How do we proceed?
Time to do some framing. You'll either need to move the shower location (assuming that is not possible) or modify the framing. This could be as simple as sistering alongside the existing joist and then cutting out the necessary area from the original joist. This will give you an extra 1-1/2" of space to install the drain.
If that doesn't work for you then you'll have to cut out the section of joist that is in the way and replace it with blocking between the next two joists. This blocking will act as headers to attach the remainder of the cut joist to. As you can imagine, to do this you are removing a bit of subfloor to give you access to the joists.
There is another option but the final result may be less than ideal. You can build your shower up on a raised pedestal, using the pedestal height to give you space to divert the drain away from the joist.
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