What is the minimum tread depth for winder treads within the clear width of the stair?

The minimum tread depth for winder treads within the clear width of a stair is defined to ensure user safety and accessibility. Winder treads are those that are narrower on one side and wider on the other, typically found in circular or spiral staircases.

The requirement for a minimum tread depth of 10 inches helps provide an adequate surface area for foot placement, decreasing the risk of slips and falls as individuals navigate the stairs. It is essential to offer enough tread depth to accommodate various foot sizes while also ensuring that users can confidently traverse the turn in the staircase without feeling precarious.

In the context of stair design, the proper tread depth is crucial for compliance with building codes, which aim to enhance safety standards in commercial buildings. The other options fall short of this minimum requirement, which is why they are not acceptable choices for winder treads in this context. Thus, the correct and code-compliant choice is 10 inches.