How to Level the Center of a House Using Jacks

Locate the sagging portion of the floor by stretching a taut string across a room from the edge of the floor at one wall across to the opposite wall. You can see where the floor sags the most where the string loses contact with the floor.

Locate the sagging area under the house in the basement or crawlspace. Remove or replace anything in the way of the floor joists under the sagging area of the floor.

Lift a 4-by-6-inch beam perpendicularly across 6 or more floor joists, depending on the size of your house. Hold the beam in place with two or three rafter ties and a few wood screws.

Place a 1/4-inch steel plate at least 12 inches square under a hydraulic jack situated under the low part of the sagging floor.

Measure the distance between the top of the jack and the 4-by-6-inch beam on the ceiling. Cut a 4-by-4-inch beam to match the measurement. Place on top of the jack and under the ceiling beam. Pump the jack until the 4-by-4 is snug in place.

Insert another supportive lally column spaced evenly apart on the ceiling beam. Tighten into place.

Raise the jack 1/8-inch per week until the floor above is level. Raise the jack just once more by 1/8-inch and Insert a permanent lally column next to it. Slowly lower the jack by 1/8-inch per week until the floor rests firmly on the permanent column. Remove the jack.