it's always something, water damage under shower

[EricU]

so I'm replacing the vanity in the master bath, and I really hate the sheet vinyl flooring in there.  Going to put down tile.  The subfloor is damaged in the corner near the shower.  Turns out the closest joist is just outside the shower.  I am not sure I have room to sneak a 2x4 in there to sister to the joist.  The joist doesn't look like it saw any water, the subfloor had a 1/4" luan plywood on top that is a goner, and then about 1/4" of the subfloor itself is punky.  

I am not sure I can come up from underneath and do anything.  There is a soffit in the kitchen, but this is back from the soffit a couple of feet.

Shower is a fiberglass unit.  I would love to replace it with tile, but that expands the project way too much.

The subfloor under the lip of the shower is bad for about 8" or so near the corner. Trying to think about how to get decent support under it and failing.

[CLETUS]

  Trying to think about how to get decent support under it and failing.

If I understand you correctly, the floor is punky 8" underneath the shower? If so, I think your only possibility is to pull the shower unit and replace the flooring.

[EricU]

actually, at least 3/8" or 1/2" of the thickness of original subfloor is still good.  And that's for only about 8" along the edge of the shower. I dug out the punky parts and it doesn't really go all the way under the bottom lip of the shower

Thinking about replacing the easy part of the subfloor and patching that part. 

I'll see if I can put up pictures later.