Laying out stair stringers can be intimidating for the first-time builder. Stringers are the backbone of your staircase. As such, they must be marked and cut accurately or the runners and risers on your stairs may not be evenly spaced. Local codes vary on the requirements for maximum rise and run (height and tread size) for individual steps. Consult your local building codes office before you begin this project.
Measure the height of the stairs. Use your tape measure to determine the distance between the finished surfaces of the upper and lower floors.
Divide the distance between the floors by the height of your risers. In most areas, the code calls for risers to be between 7 and 8 inches. For a height of 9 feet, or 108 inches, 15 steps are usually used. Dividing the total height (108) by the number of steps (15) results in an even rise of 7.2 inches for each step.
Multiply the width of your runners (the part of the stair you stand on) by one less than the number of risers. The top step will be the upper floor attached to the staircase. Code in most areas calls for the runner to be between 10 and 12 inches. Using the example in Step 2 with an 11-inch runner: 14 multiplied by 11 equals 154 inches. This is the amount of horizontal space you'll need for your staircase.
Stand on the top floor. Hold the plumb bob line against the edge of the floor and lower the bob until it contacts the lower floor. Mark this spot with a pencil.
Measure the horizontal distance of your staircase from the mark on the floor to the end of the planned staircase.
Attach a mason's line to the edge of the top floor. Attach the other end of the line to the bottom floor on the mark for the end of your staircase.
Calculate the angles at the top and bottom of the stairs, using the mason's line and a bevel gauge. Transfer both angles to the top and bottom of your stringers. Mark both angles with a pencil. These will be your cut marks.
Cut both ends of the stringer--2-by-12-inch or 2-by-14-inch lumber--with a circular saw.
Lay out the rise and run of each step with a framing square. Mark each step clearly with a pencil.
Cut out the marked steps, using a circular saw. Do not cut past the intersection of your pencil marks with a circular saw. This will weaken your stringers. Use a hand saw to complete the cuts.
Transfer the pattern to your remaining stringers, using your completed stringer as a template..
Choose your stringer material carefully. Knots adversely affect strength. Warped material will make it difficult to build an even stairway.