Applicable Codes and Standards

The family of codes published by the International Code Council (ICC) includes the building code and fire code which address in detail the requirements for safety and slip resistance in stairs and means of egress as already discussed. It is important to note, however, that while these codes apply in the majority of states in the U.S., some states have adopted either revised editions of these codes or still use their own independent codes. Hence, it is always appropriate to review the prevailing and current code requirements in any given area related to stair and egress design. While this is the appropriate starting point, there are also a number of other applicable standards that come into play and need to be addressed whenever specifying and designing with manufactured treads and nosings:

Handicapped Accessibility
The Americans with Disabilities Act (ADA) sets out specific requirements for barrier-free environments including stairways. Some of this has been codified in American National Standard ICC A117.1 (the Standard) which is appended to most building codes as the prescriptive requirements to achieve such barrier-free environments. Section 504 of this standard specifically addresses stairways indicating more stringent requirements on treads and risers. It states that the vertical risers shall be at least 4 inches and no more than 7 inches tall while the horizontal treads shall be at least 11 inches deep, which is all consistent with the International Building Code requirements for stairs. In Section 504.4 this Standard goes on to state that the surface of a tread must comply with the provisions of a floor surface as described in Section 302. These include being stable, firm, and slip resistant. The Standard and codes do not quantify slip resistance, but the ADA does recommend a coefficient of friction level of .60 or above for walkways and .80 for ramps. It is common for manufactured treads and nosings to achieve coefficient of friction levels on the order of 0.98 – 1.02 or well above the minimum called for. Other requirements in the Standard for floor surfaces include being level within a slope of 1:48 and any openings in the surface must not allow passage of a ½-inch diameter sphere. If these openings are elongated, then they must be perpendicular to the direction of travel. It is worth noting that all these same floor surface requirements also apply to ramps as cited in 405.4 of the Standard.

Cast aluminum treads and nosings Photo courtesy of Nystrom, Inc.

Nosings receive a fair bit of detailed attention in Section 504.5. First the leading edge of the tread shall have a maximum radius of ½ inch where it aligns with the riser below. If the nosing projects past the riser it is first limited to 1-1/2 inches maximum past the riser but it must also have the underside of the nosing curved or beveled. The riser below can be angled back from the nosing provided that angle is no more than 30 degrees and the projection remains within the 1-1/2-inch maximum. In terms of specifying a manufactured nosing, all of these details must be provided for to assure both compliance with the standard and that there is no protruding lip that could be a tripping hazard.

Beyond the functional walking aspects of treads and risers, the Standard adds a visual requirement in Section 504.5.1. It requires that the leading 2 inches of the tread is differentiated with a contrasting color from the rest of the tread. This can be either a dark edge on a light-colored tread (e.g., black nosing on a gray concrete tread) or a light-colored edge on a darker-colored tread (e.g., yellow safety nosing on a black stair tread). Clearly, this is meant to help visually impaired people as well as improve the general safety of everyone.

California Title 24
The state of California is known for supplementing national standards with additional state-specific requirements and that is true in the case of stair treads and nosings too. Specifically Title 24 addresses the visually impaired aspect of nosings with a variation on the Standard A117.1 requirements. It calls for the same 2-inch-wide contrasting color strip but specifies that it must be within an inch of the front of the nose of the stair. Some have interpreted this in different ways, but the stair industry has responded by providing a 3-inch nosing that can have all or any 2-inch part of it treated with a contrasting color.

Occupational Safety and Health Administration (OSHA)
Consistent with this federal agency's mission of protecting workers, they have identified requirements for stairs. Specifically in Section 1910.24f of their standards, it states, “All treads shall be reasonably slip-resistant and the nosings shall be of nonslip finish. Welded bar grating treads without nosings are acceptable providing the leading edge can be readily identified by personnel descending the stairway and provided the tread is serrated or is of definite nonslip design. Rise height and tread width shall be uniform throughout any flight of stairs including any foundation structure used as one or more treads of the stairs.” This language addresses the same concerns as the building codes and the handicapped accessibility requirements for stairs, but without the same level of detail. Therefore, by complying with the previous codes and standards referenced, OSHA compliance would seem to be met as well.

ASTM F1637 Standard Practice for Safe Walking Surfaces
The American Society of Testing Materials produces many standard specifications for many things related to design and construction. In the case of walking surfaces ASTM F1637 is the published standard available. It addresses indoor and outdoor walking surfaces indicating that walkway surfaces shall be slip resistant under expected environmental conditions and use. It goes on to state that when wet conditions are reasonably foreseeable, then an abrasive additive, grooving, texturing, or other appropriate means shall be incorporated to render the surface slip resistant. This would apply to the treads as walking surfaces on exterior stairways and they should be treated accordingly.

Clearly, then, there are numerous sources of requirements and safety standards that can be consulted on stair design and on treads and nosings in particular. It is incumbent upon the architect as designer and specifier to address these as part of the stair design and it is incumbent on the construction contractor and manufacturers of treads and nosings to follow through and provide the safe conditions called for.

These examples of extruded aluminum nosings show a ribbed profile (top) and a full abrasive profile (bottom). Images courtesy of Nystrom, Inc.

Available Tread and Nosing Products

In writing the specifications for treads and nosings, there are numerous points to consider and understand so that the correct products are called for. First is the material used in the manufacturing process. For moderate-duty treads and risers, extruded products are most commonly made from an aluminum alloy referred to as Alloy 6063 / T5. This alloy contains about 97 percent aluminum mixed with small amounts of other metals including chromium, copper, iron, magnesium, manganese, silicon, titanium, and zinc. Each of these added metals provide added characteristics either to enhance the strength and durability of the aluminum or to make it easier to extrude and machine into shape. For heavy-duty stair treads and nosings, either cast aluminum or cast iron can be specified. The common casting aluminum is referred to as Alloy 319 preferred because of its good sand casting characteristics and machining capabilities. It contains fewer added metals in the alloying process, which are limited to tiny amounts of iron, copper, and zinc for strength and durability. In some interior locations an alternative to cast aluminum is high-quality gray cast iron that complies with ASTM A-48-70. Gray iron has unique properties in the distribution of stress, corrosion resistance, unlimited design, abrasion resistance, vibration absorption, and economy. Ductile iron is available but is generally not selected for stairs since it is better suited to other uses and is notably higher in cost. All of these metal options include the ability to specify recycled content since they are very common building materials.

Once the fundamental decision is made about the metal and type of manufacturing process, the next item is the abrasive material that is added. In extruded shapes, this abrasive material is commonly a combination of aluminum oxide and a two-part epoxy which provides a durable slip-resistant surface for walking on. The aluminum is extruded with ribs running along the surface and the abrasive is placed in between. This creates the common ribbed look and is used extensively. An alternative is to specify a full abrasive product, most common for nosings, where the ribs are shorter and the abrasive material covers over the top of them across the width of the product. For cast products, a continuous coating of silicon carbide at least 1/32 inch thick is used.

Left: Concrete stairs show their deteriorated condition before using renovation treads. Right: The stairs—with new renovation treads installed—have been restored to a safe condition. Photos courtesy of Nystrom, Inc.