To use a screw jack, first employ a hydraulic jack and a post to lift the floor. Remove the wood post and nails from the underside of the floor, place the screw jack on top of a wood block on a concrete pier, just below the girder, and crank the jack so the top and bottom are touching the surfaces above and below. Use 16 penny nails to attach the jack's plates to the wooden framing. Remove the hydraulic jack.
Once the hydraulic jack is cleared, use the screw jack to move the floor up and down until the surface is level. This could be a slight or major adjustment. With major adjustments, windows may crack and doors may begin to stick. Conversely, previously malfunctioning doors and windows may begin to work thanks to the adjustment.
Screw jacks are support posts used to level floors that have become uneven due to the movement of the soil underneath the house. They are installed by entering the crawlspace under the residence and replacing wooden posts with its metal frame.
Screw jacks are made of two telescoping, heavy steel pipes. The pipe on the inside is fitted with threads and moves the top late up and down with the turn of a wingnut.