When designing stairs with a platform or a landing in the middle, a common mistake is to build a landing at an arbitrary level first, then to design and build the upper and lower stairs. lower. In ninety-five percent of cases, the upper and lower stairs have a significantly different geometry. By first analyzing your staircase and then building your platform at the right level, you will get corresponding flights.
First, let me say that building stairs is one of the most complicated aspects of carpentry. ), then NE RUSH. Precipitation usually results in poor results and wasted wood.
In summary, here are the steps (no pun intended) …
DESIGN A PHANTOM SET OF STAIRS FOR ALL THE RISING (IGNORING THE PLATFORM)  CALCULATE ONE RISE PER STAGE WHO MEETS THE LOCAL CODE (eg 7 1/8)
BUILDING A PLATFORM AT ONE OF THE LEVELS OF STEP (eg 21 3/8)
DESIGNING THE UPPER FLIGHT, USING THE SAME Rise Per Step AS THE PHANTOM STAIRCASE
DESIGN THE LOWER FLIGHT, USING THE SAME UPWARD STEP AND RUN BY STEP AS THE UPPER STAIRCASE
NOW YOU HAVE TWO FLIGHTS WITH CORRESPONDING GEOMETRY, MAKING A COMPOUND STAIRCASE
In more detail …
More importantly, you want the increase by step for both flights to be the same . Your local building code probably requires it, and even without considering the code, the stairs will look better if Rise per Step, Run Per Step and all other numbers are the same for both flights.
Have a Rise for Not Equal on Both Flights, first design a set of ghost stairs using your Total Overall Rise as if you were doing a long staircase instead of breaking it in half. (You do not really need to worry about the overall performance at this point.) Take your overall increase and divide it by your maximum local building code per step (7-1 / 2 inches is a common value.) This tells you the number of steps you will need. Since you can not have a fractional step, round this number to get an integer, then divide your Global Increase by that new number to get your Increment calculated by Not.
Here is an example:
84.5 Overall increase
7.5 Building Code Maximum rise per step
divide 84.5 by 7.5 = 11.27
11.27 is the ideal number of steps
round off to 12 steps
divide now 84.5 by 12
7.04 this is your calculated Rise Per Step
You can now build a platform or a landing for your compound staircase at a multiple of 7.04 inches, and both upper and lower flights will have the same incremental step. For example, if you build the platform at 21.12 inches (3 x 7.04), there would be three steps from the bottom. If you build it at 35.20 inches, it will be five paces from the bottom
Now, since the upper flight usually has space constraints, and the lower flight usually does not, design d & # 39; 39, first your higher flight. Use the same process for the overall elevation upper and you should end up with the same increase by step (7.04). Calculate your run by step and be sure to include a little overhang for the steps. (I've developed a stair calculator for this at: http://www.Shalla.Net .) Now, use these same elevation by step, step by step, size of the tread, and overhang the tread to design your lower flight. Your upper and lower flights will now have the corresponding geometry.