What do you call a heavy timber leading from one floor up to the next that forms the stair steps?

The term used to describe the heavy timber that runs along the sides of a staircase and supports the stair steps is known as a stringer. Stringers are essential components in stair construction, as they provide the necessary structural support for both the treads (the horizontal parts where you step) and the risers (the vertical components that connect the treads). The stringer is typically not only a structural element but also a defining aspect of the staircase's design, affecting both its stability and aesthetics.

In contrast, the riser refers specifically to the vertical portion of the stair between each tread, while the joist is a horizontal beam used to support floors or ceilings. The cripple is a framing member that is shorter than a standard stud, often used to support other components. Understanding these definitions highlights the stringer's critical role in stair construction and reinforces correct terminology in carpentry.