Minimum Stair Tread Measurements For Circular Stairs
The minimum stair tread
run for the inside radius of a circular set of stairs can't be smaller
than 6 inches. I did find one building code that requested a 10
inch minimum, instead of 6 inches.
Always double check with your building department. Remember, this
measurement is from stair tread nosing to stair tread nosing, not from
the back of an individual stair tread, to the front of the same stair
2000 International Building Code Book calls out for 11 inch minimum from the 12 inch inside radius, not 10 inches.
The minimum stair tread width for a set of circular stairs is going to follow the minimum stair tread building code, except for the fact that you will be measuring 12 inches from the inside of the circular stairway, to find your reference point, to check the stair tread minimum.
Example: You're going to be building a set of circular stairs for a private residence and when you measure 12 inches from the inside radius of the circular stairway, you have a 9 1/2 inch wide stair tread. This would be acceptable under most building codes, but would not be allowed in some other buildings that would have high occupancies or accessible to the public, where the minimum stair treads depth is 11 inches.
Attention: Don't forget to check with your local building department to verify any building codes on this website. This information could be incorrect or outdated. Building codes are updated regularly and to some building departments have different interpretations for certain building codes.