60" diameter spiral staircase exterior deck face application. Spiral stairs in most cases serve as a secondary access. When purchasing a spiral staircase that is required to be code compliant, most codes will be the same across the United States. Minimum diameter 60", baluster spacing less than 4" apart, and spiral stair rail height between 34" and 38".
30 Degree steps meet the 7 1/2" dimension, 12" from the center column and headroom 6' 6" minimum between the spiral stair landing and any spiral staircase step. All requirements listed above are the same anywhere in the United States.
Some inspectors enforce the spacing between the spiral staircase step (risers) to be less than 4" apart. Before ordering your spiral stair check with your local building department and or inspectors. Doing this will resolve any problems on the front end that will be tenfold on the back end.