How wide does a staircase have to be?
Stairways must be at least 36 in wide above the handrail (IRC R311.7.1).
Stairways must provide at least 36 inches (914 mm) of clear width at all points above the permitted handrail height and below the required headroom.
A handrail may project into that path by no more than 4½ inches on each side. At and below the handrail, the clear width can be no less than 31½ inches where a rail is on one side, or 27 inches where rails are on both sides.
Verified against
Related answers
Need this scoped to your jurisdiction?
Adopted edition and local amendments vary by city and county. Ask Donnie checks your jurisdiction and cites the exact adopted section.
Ask Donnie →General information based on the International Residential Code (a model code). This is AI assistance to verify — not legal advice. Confirm the adopted edition and any local amendments with your local building department (AHJ) and a licensed professional before you build.