Winding its way up the building s four.
Concrete spiral staircase plans.
There must be a minimum of 6 feet 6 inches of headroom at each step.
Plan on adding at least 2 inches 5 1 cm to the chosen diameter of your staircase to ensure adequate finger clearance.
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The stair railing balusters must not allow a 4 inch ball to pass through.
The handrail must be 34 to 36 inches above each tread nose.
Each tread must be at least 7 1 2 inches deep at a point 12 inches from its narrow end.