How to Level a Floor Joist

Floor joists tend to sag over time, especially when they are forced to carry heavy loads like pianos or china cabinets. Although a sagging floor joist does not necessarily bring any cause for concern in the safety of the floor, it does cause the rest of the floor to shake when people walk over it. By adding a little extra support under the sagging floor joist, the floor firms up and the items on the floor stay level. If you have a serious sag of several floor joists, you need to lift them slowly over a period of time so that the plaster and paint on the connecting walls do not crack with a quick change.

Carpenter’s level
Pencil
4- by 4-inch beam
Rafter ties
2 jack posts

Instructions

- 1
  Locate the lowest point of the floor joists under the floor by using a 4-foot long carpenter’s level in the basement. Turn it from side to side as you hold it against the floor joists. Mark the joist or joists that need lifting with a pencil.
- 2
  Attach a 4- by 4-inch wide beam across the sagging floor joists, using rafter ties screwed in place to hold up the beam. The beam should hang perpendicular to the floor joists.
- 3
  Situate two floor jack posts under the beams, lining them up with the floor joists above. The trick with successful floor jacking is distributing the weight evenly across a broad area. Place the base of the posts on a solid concrete surface or a stone footing.
- 4
  Jack the posts up until they are snug beneath the beam. Slowly turn the raising bar one rotation on each of the jack posts. Check the floor with a level and raise the jack one rotation every day until the floors are level.

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