What is the minimum tread depth for winder stairs measured from the narrower edge?

The minimum tread depth for winder stairs, when measured at the narrower edge, is indeed 10 inches. Winder stairs are different from traditional straight-run stairs as they curve and do not have a constant width. Ensuring that the tread depth is at least 10 inches helps to provide adequate foot support and safety when ascending or descending these stairs. This specified measurement is crucial for maintaining a safe and functional staircase since insufficient tread depth can lead to tripping hazards or difficulty in use.

In building codes, winder steps are typically designed to allow for a minimum tread depth to accommodate the variations in width, ensuring that at least part of the foot can rest securely on the tread as you navigate the turn. This dimension is also influenced by ergonomic considerations, as the 10-inch depth helps achieve a comfortable and stable footing while facilitating safe movement.