How do I lay subflooring ontop of an uneven wood floor?

Question

my original flooring is old tongue and groove applied directly over floor joist

Answer 1

If it's badly out of shape, you may want to try a product called "floor leveler".  It comes as a dry mix.  Just add water until it's like thin soup.  Pour over the floor.  Liquid seeks it's own level.  Allow to dry overnight then apply sub-floor.

Answer 2

sound like the house is old the best way is to remove the boards that are warped and replace with 3/4 plywood or osb.

Answer 3

apply 3/4  ply  board over the top with liquid nail .and s***w it

  it will come level .......