504.5 Nosings.
The radius of curvature at the leading edge of the tread shall be 1/2 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 1 1/2 inches (38 mm) maximum over the tread below.
(a)
radius of tread edge
(typical for all profiles)
(b)
angled riser
(c)
curved nosing
(d)
beveled nosing
Figure 504.5 Stair Nosings
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