Handrail extensions are required for all commercial stairs. Handrails should return to a wall, guardrail or walking surface, or should be continuous to the handrail of an adjacent stair flight or ramp run. If handrails are not continuous, they should extend a minimum of 12 inches beyond the top riser, and a minimum of 12 inches plus the depth of one tread beyond the bottom riser. At the top, the handrail extension should be parallel to the ground. At the bottom, the extension should continue to slope for a distance of the depth of one tread from the bottom riser; the remainder of the extension should be horizontal.
Exceptions include handrails within dwelling units that are not required to be accessible, and aisle handrails in Group A occupancies.
Clear space between handrails and wall surfaces are required to be a minimum of 1.5 inches. Circular handrails should have an outside diameter of at least 1.25 inches, and no greater than 2 inches. Non-circular handrails should have a perimeter dimension of at least 4 inches, and no greater than 6.25 inches, with a maximum cross-section dimension of 2.25 inches.
Also keep in mind that guardrails are required along stairways more than 30 inches above grade, and should be a minimum of 42 inches high.