How to Add a Load Bearing Wall Due to a Sag in the Floor

Decide where you need a load-bearing wall. If you are replacing a missing wall, look at the beam or joists to see where a wall was removed. In most wood frame construction, a load-bearing wall should be installed directly underneath a load bearing wall on the story above or directly underneath a main supporting beam.

Nail a two-by-four strip to the joists or supporting beam to the length required for your wall. Using longer nails, nail a second two-by-four strip beneath the first one, staggering any joints. Starting at one end of your wall, drop a plumb line from one side of this double plate to the floor and mark the spot where the bob touches. Repeat at the middle of your wall and at the other end. Snap a chalk line to connect the marks. Lay a two-by-four along the chalk line as the floor plate.

Secure a piece of 4-by-6-inch bolster beam to the ceiling joists or support beam with hanger plates. Place this bolster beam next to the ceiling plate. Place another piece of 4-by-6 beam on the floor next to the floor plate. Put a steel plate on the bottom beam and put the hydraulic jack on it. Put the steel column on the jack and another steel plate on top of the column. Raise the sagging floor until it is level as part of a long-term process. Raise the floor bit by bit, working 1/8 inch per day. Use long bolster beams and multiple jacks and columns if necessary.

Measure the distance between the floor and ceiling plates. Cut two-by-four studs to the length required and fit them between the floor and ceiling plates. Install the studs 16 inches apart with the wider sides at right angles to the floor and ceiling plates. Toenail them in place. Remove the jack and bolster beams.

Frame openings in your load bearing wall by installing two-by-four doubled studs at each side of the opening. Cut the second stud short to provide a shelf for the header over the opening. Install a doubled two-by-four header at the top of the opening. Set the header with the wide sides vertical. Install short two-by-four studding between the header and ceiling plate. Nail pieces into place. Cut out the floor plate in the opening.

Install 4-by-8-foot sheets of ½-inch chipboard or plywood sheathing on your wall for added strength. Nail the sheets to the studs. Cut the sheets as needed to fill in odd spaces. Nail the pieces in place. Paint the sheathing. If desired, you can finish the wall with drywall and then paint.