120 yr old house floor sag correction

[HayZee518]

I agree with the lally columns but I would install at least three columns. I don't understand the 4x6s. use a concrete footing at each column location. make the footing 24" square and 8 inches deep.

[M.Chete]

I just bought an old colonial built in the late 1800's. It sags in the middle and I am planning to spend the next few months working on it. I do not anticipate 100% correcting this problem, only raising the floor at the center, reinforcing the floor as to lay down new flooring while preventing further sag.

I plan to:

1. raise the floor joists using adjustable lally columns. I planned to get 4" x 6" pieces of lumber and afix to the sagging joists and floor, insert the columns slowly raise them over a month or until the floor is no longer sagging. Then place a Lally column or build a load bearing wall to add permanent support for the floors
2. After the floor is leveled and supported, pouring self leveling compound or using floor matting and lay down new flooring.

Any ideas on how to make this work or any flaws in this plan? I am a new DIYer and any and all feedback will be greatly appreciated.