How to Cut a Skirtboard for Stairs

Extend a tape measure between the first floor and second floor to determine the vertical distance. Divide this measurement by the riser or step height, which is typically between 7 and 8 inches for residential stairs.

Multiply the measurement by the depth of the tread to determine the stairway “run.” Stair treads are 11 to 13 inches wide, and include the nosing or overhang. Multiply the number of treads by 15 inches to calculate each skirtboard’s length.

Place the 1-by-10-inch skirtboard stock flat across two sawhorses. This board will serve as the template for the other stair skirtboard. Determine one end of the stock as the base.

Set the framing square on the edge from which you will cut notches for the tread and risers. Adjust the square so its shorter arm lines up against the edge of the board set for the desired riser’s height. Trace along the edge of the square with pencil.

Adjust the longer arm of the square to match the desired depth of the stair. Trace along the edge of the square with pencil.

Form a 90-degree angle from the topmost tread line where it joins the outer edge of the skirtboard. This line serves as the cutline for the first riser. Also mark the riser line at the desired riser’s height, minus the thickness of the desired tread material. The point at which both lines intersect forms the cut that falls flush on the floor at the top of the stairs.

Repeat the previous step, placing the tread mark at the edge of each previous riser mark, until you mark the correct number of treads and risers on the skirtboard.

Measure from the edge of the top tread line to the tread depth, minus 1 inch, and make a 90-degree angle at the tread line to form the top end cut.

Cut along the lines on the skirtboard to the corner where the back of each tread meets the end of the riser using a circular saw. Use a handsaw to form the cuts along the inner corners.