A third stair stringer should be installed when stairs exceed what width?

A third stair stringer is needed for stairs that exceed a width of 2 feet 6 inches to provide adequate support and safety. When stairways are wider than this, a single stringer on either side may not sufficiently support the tread and riser structure, leading to potential sagging or failure due to insufficient structural integrity.

The International Building Code provides guidelines for stair construction, emphasizing the need for additional support as the width increases. Beyond 2 feet 6 inches, adding a third stringer helps distribute the weight more evenly and enhances the overall stability of the staircase, ensuring safety for users. This requirement is crucial in both residential and commercial construction to maintain compliance with safety standards.