11B-504.5 Nosings

Note: This document or portion of document references a state or local code that aligns with the 2010 ADA Standards requirements.

11B-504.5 Nosings.

The radius of curvature at the leading edge of the tread shall be ½ inch (12.7 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 1¼ inches (32 mm) maximum over the tread below.

Exception: In existing buildings there is no requirement to retroactively alter existing nosing projections of 1½ inches (38 mm) which were constructed in compliance with the building code in effect at the time of original construction.

Advisory 11B-504.5 Nosings. While Chapter 10 may allow larger radius of curvature at the leading edge (nosing) of the tread, this radius must be no larger than ½ inch to comply with both Chapter 10 and Chapter 11B requirements.

Additionally, because it is possible to catch the top of one’s shoe on the underside of stair nosings, access compliance regulations require the underside of nosings to be free of abrupt changes – a beveled slope or non-square underside. ◼