Use a string to watch the floor come up.
How to jack up a wood floor.
Jacking must proceed slowly.
Raising up a shed w a car jack and adding concrete blocks.
Stack 8 x 12 blocks two wide in a criss cross pattern until they as close to the bottom of the girders as possible.
It has to be jacked up slowly over days or even weeks to avoid cracking drywall plaster windows and even structural elements.
Once the floor is at the right level jack it up just a little bit higher.
You cannot jack up a house in one day.
Jack up that portion of the house and place new footers.
Anything involving 20 ton house jacks will take time.
As with other structural repairs jacking must also be done appropriately.
Keep an eye on the girder so that it does not get out of position and try to roll.
You cannot simply put a screw jack under the lowest spot and start turning.