A third stairway stringer is recommended when the stair width exceeds how many inches?

A third stairway stringer is recommended when the stair width exceeds how many inches?

• A. 30 inches
• B. 28 inches
• C. 32 inches
• D. 34 inches

Answer: (A)

When a stair run gets wider, you need additional support to keep the treads from sagging and to maintain solid handrail and riser alignment. A third stringer adds a central support, distributing the load more evenly across the treads and reducing deflection. That extra support makes the wide run safer and more durable, because the two-stringer setup can’t share the load as effectively once the width crosses the threshold where stiffness becomes a concern. In narrower stairs, two stringers typically suffice, but as the width grows beyond that point, adding a third stringer is the recommended practice.