So the walkable portion of the stairway in the condo I inspected today was only 33 1/2 inches between the base boards. I was always under the understanding that this dimension was a 36 inch minimum but am having trouble finding anything to back me up. I will delve into the dreaded C-Book but if someone has anything let me know.
The 36" requirement is not for tread width, but for stairway width wall to wall, measured at and above the handrail height.
Stairways shall not be less than 36 inches (914 mm) in clear width at all points above the permitted handrail height and below the required headroom height. Handrails shall not project more than 4.5 inches (114 mm) on either side of the stairway and the minimum clear width of the stairway at and below the handrail height, including treads and landings, shall not be less than 31.5 inches (787 mm) where a handrail is installed on one side and 27 inches (698 mm) where handrails are provided on both sides.
Thanks man! That’s exactly what I found.