On Nov 11, 2:42 pm, pollyfan wrote:
No wall under the proposed space. The joists are 2x9, and where the
bath will go they are (oddly) 4", 12", 13", and 4" apart! Also the
floorboards above them are set diagonally across them--don't know if
that spreads the load any differently.

Your house sounds like it was well-built. The diagonal laydown is more
to reduce stress and buckling along the two orthogonal horizontal axes
of the house. I had an old house with this type of construction.
Tongue and groove base floor (diagonal laydown) with solid oak
flooring above. The oak boards ran parallel to one of the walls,
naturally.