So, you thought you would build a deck or add another level to your house, but now when it comes time to put in the stairs, you aren't quite sure how to do it? This is just the type of question you should ask CarpenterKen. Ken will post the answer on the CarpenterKen website and, if you request it, let you know when the answer has been posted. The first step in stair layout is to determine the overall distance between the lower level and the upper level. It is important to consider everything when you arrive at this dimension.
You will need to know the absolute level of both the upper and lower floors. Consider what the floor covering will be on both levels if this is an interior stairway, and consider what the tread will be on the stairs. Let's look at an example. Say you are building a stairway in a new addition that will go from a ground floor level that will have ceramic tile laid on concrete slab to an upper level that will have hardwood over plywood framing. The stairway will also have hardwood treads. The overall distance from the top of the concrete floor to the top of the rough plywood framing above is 8 feet 10 inches.
If you will be installing tile on the concrete floor that is 1/4 inch thick and hardwood on the upper floor that is 3/4 inch thick, the net difference will be 8' 10-1/2". The maximum rise (step height) is 8 inches, so divide the total distance by 8 to get the minimum number of steps (treads) 8 x 12 + 10.5 = 106.5 inches / 8 = 13.3125 so you will need at least 14 risers and 13 treads.
Divide the total net difference by the number of risers to get: 106.5 / 14 = 7.6 inches per riser or just under 7 5/8 inches. The minimum tread is 9 inches, but a common way to determine what the tread should be is to take 2 times the riser height from 25 and make that the tread size.
In this example, 2 x 7 5/8 = 15 1/4 inches from 25 leaves a recommended tread size of 9 3/4 inches. This is an approximate number, but the rule of 2 times the rise plus the tread equal to 25 will generally provide a stair that is comfortable for most people to climb. Depending on what you will be using for tread material and riser boards, you can now determine exactly what it will take to cut a stair stringer. This will generally be cut from a 2" x 12" and layout can be done with a framing square. Set the square on the edge of the 2" x 12" so that the rise length is on one leg and the tread depth is on the other leg, and then draw along the two faces of the square. Move the square along the 2" x 12" and repeat.
For some drawings that illustrate the technique you can go to the carpenterken website.
Jerry Cahill, publisher and webmaster, supports a carpenter website under the name of carpenterken.com