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ABA Accessibility Standard for GSA Facilities Pocket Guide

504.5 Nosings.

The radius of curvature at the leading edge of the tread shall be ½ inch (13 mm) maximum. Nosings that project beyond risers shall have the underside of the leading edge curved or beveled. Risers shall be permitted to slope under the tread at an angle of 30 degrees maximum from vertical. The permitted projection of the nosing shall extend 1½ inches (38 mm) maximum over the tread below.

Figure (a) shows vertical risers where the radius of curvature of the leading edge of each tread is ½ inch (13 mm) maximum.

 

Figure (b) shows angled risers.  Risers can slope at an angle of 30 degrees maximum from the vertical. 

 

Figures (c) and (d) show curved and beveled nosings, respectively.  The maximum projection of the nosing is 1½ inches (38 mm) beyond the rear of the tread below.

 

Figures (c) and (d) show curved and beveled nosings, respectively.  The maximum projection of the nosing is 1½ inches (38 mm) beyond the rear of the tread below.

Figure 504.5 Stair Nosings

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