Is there a crawl space or basement below the floor? If there is a crawl space, then you will have to work with the jacks while laying down. If it's the basement, then jacks while standing up.
, Draw on some paper a floor diagram and indicate what direction the floor is leaning. This will help a lot when the jacking begins., Generally there are posts and beams under the floor joists. If a pier that the post is standing on has sunk into the ground you will need to lift the beam off the post and replace the post with a taller one., Place the jack (I prefer at least 25 ton hydraulic. or a house screw jack) on the plywood and then I use a piece of thick hardwood between the jack's ram and the beam to prevent damage to the beam. If two beams meet on the post that is sunk then a jack on both sides of the post is required., Check the floor regularly to make sure you do not over level it., Once the floor is brought to level you check all around to see if there is any other areas that are still low. This is done by placing the level on the floor in several different positions and areas as before., Cut a replacement post of the same dimension lumber that was removed. You can go larger lumber but never smaller. But the best is to go with the same dimension. Also it is not a good idea to try to raise the pier block up by placing more dirt under it and then putting the old post back in. You aren't going to be able to compact the soil enough to keep it from sinking back down under the weight of the house., This will ensure moisture doesn't come up through the concrete and get to the wood. If the reason the floor sank is due to a rotten post and there was no tar paper you can now see what happens. Now put the weight of the house on the post. Keep it lined up with the sides of the beam. Check the floor for level again to make sure you're still good., Once the post is replaced it needs to be fastened to the beam. If the beam and the post is the same width (they should be) then just nail a 2X4 piece on both sides of the beam down the side of the post and nail to the post. Then you fully remove the jacks and lumber they sat on and put them away. You're done!
Determine where the floors supports are.Put a level on the floor in several different positions in the affected room to determine which way the floor is leaning.
Check the perimeter of the room to see if there are any additional areas that are out of level.
Get the jacks under the floor.
Place a couple of two foot long pieces of 2X6 lumber side by side on the ground under the beam and place a 3/4" plywood 1'X1' on top of the 2X6's.
Begin jacking up the beam or beams and make sure you jack equally with two beams.
Look for low areas.
Remove the old post and measure the distance between the beam and the pier.
Place a piece of tar paper on top of the concrete pier and the new post on top of the paper.
Fasten.
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