Hi, everyone! This looks like a great (and busy!) forum, so I guess that makes it a great place to ask this question.
I have a stretch of about four feet in my kitchen floor where it sags slightly between joists. The joists are healthy and so is the subfloor. So here's what I'm thinking about doing and maybe some of you can advise as to whether this would work or would/wouldn't be a good idea.
I plan to cut a piece of wood (either plywood or lumber) to fit between the joists, and about four feet long. I want to jack it up slightly against the subfloor until level, then attach it in that position with braces against the inside of the joists.
Do it between the joists with blocks not along the joists. For example if your joists are 16" on center your cuts would be 14-1/4". Place a cut every 16" on center starting at any cross seam in the subfloor that may be there. Fasten the blocks through the related floor joists with two fasteners per side then toenail the blocks from the bottom of the block upward into the related joists. Six fasteners per block.