4.9.1* Minimum Number. Stairs required to be accessible by 4.1 shall comply with 4.9.
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. Open risers are not permitted.
Each stair tread is 11 inches (280 mm) deep minimum with a sloped riser. The nosing shall project no more than 1-1/2 inches (38 mm).
4.9.3 Nosings. The undersides of nosings shall not be abrupt. The radius of curvature at the leading edge of the tread shall be no greater than 1/2 in (13 mm). Risers shall be sloped or the underside of the nosing shall have an angle not less than 60 degrees from the horizontal. Nosings shall project no more than 1-1/2 in (38 mm).
Figure 18(a) Flush Riser. Each stair tread is 11 inches (280 mm) deep minimum with a sloped riser. The nosing shall project no more than 1-1/2 inches (38 mm).
Figure 18(b) Angled Nosing. An angled nosing may be used with a 60 degree angle measured from horizontal. The nosing shall project no more than 1-1/2 inches (38 mm).
Figure 18(c) Rounded Nosing. A rounded nosing may be used with a 60 degree angle measured from horizontal. The nosing shall project no more than 1-1/2 inches (38 mm).
4.9.4 Handrails. Stairways shall have handrails at both sides of all stairs. Handrails shall comply with 4.26 and shall have the following features:
(1) Handrails shall be continuous along both sides of stairs. The inside handrail on switchback or dogleg stairs shall always be continuous
Plan. Handrails that are not continuous must have a horizontal extension at the top and bottom of the run. A minimum 12 inch (305 mm) horizontal extension is required at each top riser (indicated in the figure by the dimension X). A minimum 12 inch (305 mm) horizontal extension plus the width of one tread is required at each bottom riser (indicated by the dimension Y).
Elevation of Center Handrail. Illustrates a continuous handrail without a horizontal extension.
(2) If handrails are not continuous, they shall extend at least 12 in (305 mm) beyond the top riser and at least 12 in (305 mm) plus the width of one tread beyond the bottom riser. At the top, the extension shall be parallel with the floor or ground surface. At the bottom, the handrail shall continue to slope for a distance of the width of one tread from the bottom riser; the remainder of the extension shall be horizontal. Handrail extensions shall comply with 4.4.
Extension at Bottom of Run
Extension at Bottom of Run. Illustrates a horizontal extension at the bottom of a stair. A 12 inch (305 mm) horizontal extension is shown plus the width of one tread. In the drawing this distance is indicated by the dimension Y. The tread width is measured from the front of the nosing to the front of the next nosing of the tread above, measured horizontally. The end of the handrail extension is returned down towards the floor and then to the support post.
Extension at Top of Run
Extension at Top of Run. A 12 inch (305 mm) horizontal extension is shown. The extension starts at the nosing of the top tread and continues for at least 12 inches (305 mm) before the railing turns. This is also indicated as dimension X. The figure illustrates a handrail extension that returns to the support post with a lower horizontal segment less than 27 inches (685 mm)above the floor.
(3) The clear space between handrails and wall shall be 1-1/2 in (38 mm).
(4) Gripping surfaces shall be uninterrupted by newel posts, other construction elements, or obstructions.
(5) Top of handrail gripping surface shall be mounted between 34 in and 38 in (865 mm and 965 mm) above stair nosings.
(6) Ends of handrails shall be either rounded or returned smoothly to floor, wall or post.
(7) Handrails shall not rotate within their fittings.
4.9.5 Detectable Warnings at Stairs. (Reserved).
4.9.6 Outdoor Conditions. Outdoor stairs and their approaches shall be designed so that water will not accumulate on walking surfaces.