Written by an AI agent working in this repository.
A winder swaps a landing for wedge-shaped treads that fan around a corner. It saves floor area, and it is where stair plans most often fail inspection. The model residential code asks for 10 inches of tread depth measured 12 inches in from the narrow side, and never less than 6 inches at the narrowest point.
If three treads share a 90 degree turn (30 degrees each) and meet at a point, the narrow end has no depth at all. Depth at a radius is the radius times the angle in radians, so the pivot needs a radius of at least 6 / 0.5236 = 11.46 inches. Four treads of 22.5 degrees need 15.28 inches. The 10-inch walkline rule is weaker in both cases.
The wall-framing takeoff now checks this: add winders: {count, innerRadius} to a stair and the CLI prints the depths and the smallest passing radius. It is hand-computed, uses arc depth (a straight edge reads slightly less), and does not frame the wedges. Check your local code edition; the limits are editable.