Stairs are used in a wide variety of commercial buildings. They provide access to different floors and can be installed both inside and outside the building. Although there are many different designs and materials, there are basic regulations that must be followed when constructing stairs. These regulations include stair treads, handrails, landings, and more. The International Building Code (IBC) regulates commercial stair construction.
Stairways shall have handrails on both sides of the staircase. Handrails shall extend horizontally twelve inches past the top riser. In ADA-compliant buildings, the handrails must extend a further 12 inches beyond the bottom riser.
Stair treads must be 11 inches in depth. Treads must be beveled or have a partial non-slip surface. Treads may be angled back at a slight return, but beveling must not exceed 0.5 inch (12.7 mm).
Landings must be at least 48 inches deep and may be more than one-half the width of the stairway. In addition, the leading edge of the walking surface of the landing must be at least four inches wide. Additionally, the leading edge of the tread at the nonuniform height risers must be equipped with a distinctive marking stripe. This stripe must be slip resistant, and it must be visible in the descent.
Guards at the end of an aisle, gallery, or balcony shall be balusters that are at least eight inches in diameter. Openings for guards must not allow spheres that are four inches in diameter or more.
Alternate tread devices are commonly attached to the center rail in an alternating fashion. These devices limit the occupants of the stairs to five people. Alternate tread devices cannot exceed a total area of 250 square feet. The front portion of the stair tread will extend over the riser, and the leading edge of the tread will meet the riser at an angle of up to 90 degrees.
The American with Disabilities Act (ADA) requires uniform stair tread widths and heights. For private stairways serving less than ten occupants, the maximum riser height is eight inches. There must be a handrail extending at least 12 inches past the bottom riser in the stairway.
Stairs and ramps must be fire-resistant. Doors that open onto a landing must not project more than seven inches into the landing. Exit stairways must be protected by an enclosure that is at least two hours fire-resistant.
Winders cannot be used in the required stairways unless they are attached to the dwelling unit. When a winder is mounted on a post, it must be at least eleven inches deep when a tread is a quarter-inch from the narrow edge of the post. It also must not overhang the post more than 102 mm.
Landings are required in class 9a buildings. They must be two meters long and 600mm wide. They must be deep enough to allow the stretcher to be pushed through. Depending on the stair type, landings may be as small as 4 inches in depth.