- 1). Use the tape measure to determine the vertical distance between the surface of the first floor and the surface of the second floor. This measurement will be used to determine the number of steps needed in the stairway.
- 2). Divide the above measurement by a number that gives you a step height, or riser, between 7 inches and 8 inches each. (Note: The comfortable standard step riser is approximately 7-1/2 inches for residential stairs.)
- 3). Multiply this number by the step tread width to determine the run of the stairway. Stair treads are typically 10 inches to 11 inches wide, including overhang or nosing.
- 4). Place one of the 2 x 12 boards on sawhorses for layout. This board will be the first stair "stringer" and, once cut, becomes the template for marking the remaining two 2 x 12 boards.
- 5). Beginning at the base or bottom end of the 2 x 12 board, place the framing square on the edge where the tread and riser notches will be cut.
- 6). Adjust the framing square so that the smaller arm aligns the riser measurement determined in Step 2 with the edge of the board. Align the wider arm of the framing square with the tread width determined in Step 3. Be sure to begin the first tread line as a distance from the end of the 2 x 12 board to allow for the first riser height to be cut or approximately 10 inches.
- 7). With the square held firmly in place, scribe a pencil line along the edge of the framing square at both angles. Please note that all markings must be done from the same edge (inside or outside) of the framing square on which the riser and tread measurements are set.
- 8). Mark a 90-degree angle from the board edge of the first tread line to mark the cut line of the first riser.
- 9). Measure and mark the first riser line at the riser height minus the thickness of your tread material. (This cut is parallel to the first tread and will set on the floor at the beginning of the stair.)
Repeat Step 6, placing the tread measurement at the edge end of the previous riser mark. This step is repeated until the correct number of treads and risers established in Step 2 have been marked on the board.
The top end cut is determined by marking a 90-degree angle to the tread line, measured from the front edge of the step line to the depth of the tread minus the nose overhang and thickness of the riser material. Example: For a 1-inch tread nose overhang and ¾-inch riser boards, the cut would be the tread width minus 1 ¾ inches.
Cut the 2 x 12 board on the pencil marked lines with a circular saw. Use a handsaw to finish cutting at the inside corners.
After verifying the fit, use the finished stringer as a template to cut the remaining two 2 x 12 boards. Stringers are installed with one on each side of the stairwell opening and one positioned at the center.