How to Build a Knee Wall for a Staircase

Measure the length of the three sides of the space where you're building the knee wall with a tape measure. Measure the angles of the two slanted corners with a protractor. You can purchase a protractor designed for construction use at your local home improvement store.

Cut a bottom plate for the frame from a 2-by-4 board. Cut the bottom plate to match the length of the bottom section of the knee wall, then cut one side of the board at an angle with a miter box, matching the angle you measured in Step 1. Wear safety goggles when sawing the wood. The frame for the knee wall is configured so the 4-inch edge of the 2-by-4 is placed on the floor.

Cut a 2-by-4 board to be the frame's top plate. Cut the board to the required length, then cut the edges to the correct angles, using the miter box. The 4-inch side of the 2-by-4 will be placed against the bottom of the staircase.

Cut the end stud for the frame to the correct height, then cut the top edge of the end stud to the correct angle for the space, using the miter box.

Nail the straight edge of the end stud to the end of the bottom plate that does not have the miter cut. Nail the top plate to the top of the end stud and to the sloped end of the bottom plate to form a triangular-shaped frame that fits inside the space underneath the staircase.

Measure and cut studs to fit inside the frame. Cut the top edge of the studs with the miter box, and use enough studs so they're spaced no more than 16 inches apart.

Place the studs inside the frame, then nail them to the top and bottom plates.

Slide the assembled frame into position underneath the staircase, and nail the bottom plate to the floor, the end stud to the wall, and the top plate to the staircase.

Cut sheets of 1/2-inch drywall to fit over the framing. If the frame is small enough, you may be able to use a single sheet of drywall.

Place the drywall into position over the framing, then attach it to the framing with drywall screws, using one screw every 8 inches.

Apply joint compound over the heads of the drywall screws, smoothing it with the putty knife. If you used more than one sheet of drywall, apply joint compound over the joints between different sheets, and place a strip of drywall tape over the joint. Press the tape into the drywall with the putty knife. Allow the joint compound to dry overnight.

Sand the joint compound smooth with fine-grit sandpaper and wipe the dist off with a dry rag. If you had to apply drywall tape and joint compound to seams between different sheets, apply another layer, allow it to dry overnight, and sand it smooth again.

Apply a coat of primer to the knee wall, allow it to dry, then paint the drywall with two coats of paint. Allow the first coat of paint to dry before applying the second coat.

Nail trim to the base of the knee wall that matches the trim in the rest of the room.