Section 406 Aisle Stairs

Aisle stairs shall consist of a series of treads and risers that extend across the full width of the aisle. Aisle stairs shall be constructed in accordance with the requirements of this section.

Tread depth shall be a minimum of 11 inches (279 mm). The tolerance between adjacent treads shall not exceed 0.188 inch (408 mm).

Treads constructed of more than two elements shall not have a gap of more than 0.25 inch (6.4 mm) between adjacent tread surfaces. Treads constructed of grating shall not permit a sphere of 0.25 inch (6.4 mm) in diameter to pass through.

Riser height shall be not less than 4 inches (102 mm) nor more than 8 inches (203 mm).

Risers shall be of solid construction.

1. Openings in risers are permitted provided the opening does not exceed 0.5 inches (12.7 mm) in height and width.
2. Solid risers are not required in telescopic and folding seating where necessary to maintain opening and closing operational clearances.

Stair treads and risers shall be of uniform size and shape. The tolerance between the largest and smallest riser or between the largest and smallest tread shall not exceed 0.375 inch (9.5 mm) in any flight of stairs.

Treads and risers located in transition areas between adjacent tiered seating elements, parabolic seating configurations or onto or off of tiered seating are not required to be of uniform depth or height where a mid-aisle handrail is provided. The handrail shall meet the requirements of Section 409. Mid-aisle handrails in transition areas shall extend the full length of the transition and a minimum of one tread depth, parallel to the run of the aisle stairs, above and below the uppermost and lowermost riser in the transition. Where extensions of the aisle handrail interfere with adjacent means of egress, the handrail extension shall terminate at the riser.

Where tread or riser nonuniformity exceeds 0.188 inch (4.8 mm), a distinctive marking stripe shall be provided on each tread adjacent to the non uniform tread or riser. The marking shall be provided on each tread at the nosing or leading edge such that the location of each tread is readily apparent when viewed in descent. Such stripe shall be a minimum of 1 inch (25 mm) wide and a maximum of 2 inches (51 mm) wide.