Old house floor question...

[jplinville]

As you may know, my house is 115 years old...and has been showing it's age a bit more recently. Anyway, the floors have had a bounce to them since moving it. I checked the old blocking between the joists, and have found them to be a weak design...1X4, cut at an angle and installed diagonally. What my dad and grandpa did to old houses like this was to block it with 2X4, cut straight. They did that to an old house for my brother, and it seemed to work very well...so that's going to be my first task.

Now, if blocking doesn't work, I have the option of a floor screw jack. I can place one in the center of the floor in the basement, tighten it up, then box it in and forget it. What my question is...What sized beam should I use to span the floor, perpendicular to the joists, to rest between the jack and the joists? Would 4X4 work, or should I go with a bit more heft, and wrestle a 6X6 down there?

I'm hoping that blocking fixes my concern for now...more time consuming, but I won't be wrestling beam around and in between the stairs and chimney base.