How to Install a Screw Jack to Level Your Floor - dummies

How to Install a Screw Jack to Level Your Floor

By James Carey, Morris Carey

If your home is built on expansive soil and, thus, subject to regular movement, a screw jack can be used in lieu of solid wood posts between the concrete piers in the crawlspace and the girders that support the floor joists.

A screw jack is a metal support post that can be adjusted to level the floor. It consists of two heavy steel pipes, one inside the other. The inside pipe is threaded and adjusted up and down by turning a large wing nut. The screw jack is attached with nails to the underside of the girder and to the wood block atop a concrete pier.


Screw jacks can generally be found at local hardware stores and home centers. Here’s how to install a screw jack:

  1. Use a hydraulic jack and a short post to shore up the floor during this process.

  2. Use a hammer, a nail puller, and a sledgehammer to remove the existing underpinning wood post and nails.

  3. Center the screw jack below the girder and on top of the wood block on the concrete pier.

  4. Adjust the screw jack so that the top and bottom plates are flush to the wood surfaces above and below.

  5. Drive 16-penny nails through the holes in the plates and into the wood framing.

  6. Lower the hydraulic jack to transfer the floor load to the new screw jack.

  7. Adjust the screw jack up or down to achieve a level surface.

In some cases, when radically adjusting a floor, don’t be surprised if windows crack and doors stick. On the other hand, don’t be surprised if a few of those once-sticking doors and windows now operate just fine. It’s amazing what a little trek under the house can do!