Is it accepted to use sheet metal for fireblocking? What thickness? It would be great if a roll to flashing could be used and staple it up as you go but I am thinking it is too thin even though it would stop airflow.

The house in question is a turn of the century home that never had closets originally. At some point (1990s), somebody framed in a closet with bifold doors and wood paneling. Very little actually held the new wall to any part of the structure. A few nails into the existing plaster and lath walls, and the bottom plate was nailed into the hardwood floor. So, that went away. What I'd like to do is replace it with a sliding "barn door." The wall runs parallel to the ceiling joists, so when I rebuild it, I'm going to need to get up into that and add some blocking (since it won't line up with the joists). I'm also going to add a beefier header, since the barn doors will be hanging from a rail on it. My biggest concern, though, is the connection of the bottom plate to the floor. Because the barn doors hang off of one side of the wall (rather than in line like with a swinging door), I'm worried that the weight distribution will start torquing on the framing. If I just nail the new bottom plate back into the hardwood, do you think I risk the nails pulling out, or other problems?