ITEM 4.9.2 | TREADS AND RISERS

On any given flight of stairs, all steps shall have uniform riser heights and uniform tread widths. Stair treads shall be no less than 11 in (280 mm) wide, measured from riser to riser (see Fig. 18(a)).

Open risers are not permitted.

(a) Flush Riser	(b) Angled Nosing	(c) Rounded Nosing
Fig. 18 Usable Tread Width and Examples of Acceptable Nosings