How to Cap a Knee Wall on Stairs

Measure the length of the top surface of the knee wall using a tape measure. Add 2 inches to this measurement to determine the length for your knee wall cap. A simple way to think of the knee wall cap is that it covers over the top surface of the knee wall. The extra 2 inches will allow the cap to overhang past the front edge of the knee wall to make it more decorative.

Lay the hardwood board on the table of a radial arm saw. Measure the length you determined for the knee wall cap across the length of the board with a tape measure and mark it onto the board with a pencil. Pull the trigger on the saw and guide it down through the board in an even motion just fast enough to allow the blade to cut through the wood. Raise the saw back up to the start position and release the trigger to complete the cut.

Place the cut knee wall cap board on a work surface. Rout around the top side and front edges of the board using a router equipped with a decorative edge bit. Rout in a counterclockwise motion.

Sand the routed edges with a fine-grit sanding pad in the same direction as the wood grain to achieve a smooth surface.

Lay the board flat on the top surface of the knee wall with the routed edges facing up and the front edge facing the front of the staircase knee wall. Center the board so that the sides overhang past the knee wall an equal amount on each side.

Hammer finish nails every 4 to 6 inches through the top of the board into the top surface of the knee wall. Center a nail set over each nail head and tap the top of it with a hammer to set each nail 1/16-inch below the surface of the wood.

Fill the nail holes with wood putty using a putty knife. Allow the putty to dry 24 hours and sand it flush with the surface of the wood using a fine-grit sanding pad.

Brush on two even coats of wood finish using a paintbrush. Allow the first coat to dry at least four hours. Wait 24 hours before touching the final coat.