Most building codes require staircases to maintain consistent tread width.
By default, Chief Architect measures the length and tread width of a stair section along a walk line. The walk line is typically located 12" or 30 cm from the edge of the stair section. On curved stairs, it is measured from the inside edge of the curve.
The walk line distance from the staircase edge can be specified on the Style tab of the Staircase Specification dialog. The walk line feature can also be turned off and tread width measured at the tread center. See "Style Tab".
When the walk line is used on a curved stair section, the number and/or width of treads in a section or subsection changes when the inner edge is moved because the walk line is measured from this inner edge. You should set the stair section width to its final value as early as possible.
There are two ways to keep tread width even throughout a stair section made of multiple subsections.
The first way to maintain tread width is to Lock Tread Width to a specified value on the General tab of the Staircase Specification dialog. See "General Tab".
Once locked, any changes to the length of the stair section are made in full tread increments, maintaining the specified tread width. A stair section consisting of multiple subsections must have the tread width locked so the tread width of each subsection is set to the same value.
Uniform tread width can also be maintained by selecting Ignore Subsection Boundaries on the General tab of the Staircase Specification dialog. This maintains a consistent tread width throughout a stair section without regard to subsection boundaries. The tread width value may change when the stair section is edited, but remains consistent throughout all subsections. See "General Tab".
Because the program is ignoring the boundaries where one stair section merges with another, the treads where a straight section joins a curved section may angle to accomodate the adjustment.
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