Stairs may be taken for granted, but they are complex assemblies that require attention to detail in their construction. They require the correct components put together in the right proportions for the greatest durability and to allow for the safest use. Contractors and installers must meet specific standards for these structures to receive approval from building authorities.
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Local and state building jurisdictions may have only slight variations in their construction standards because all base them on the International Residential Code, which was developed and is maintained by the International Code Council. The council is a nonprofit member organization that was founded in 1994 to combine three sets of building codes common at the time. It streamlined any duplicate information and eliminated conflicts. One national standard ensures that homeowners and contractors who learn about stair construction in one part of the U.S., can use that knowledge and skill in any other part of the country.
The IRC defines a stair as a change in elevation, consisting of one or more risers, and a stairway as one or more flights of stairs, with connecting landings and platforms to provide uninterrupted access from one floor level to another. A flight is a continuous run of treads. Treads are stair steps, or the flat horizontal surfaces of a stair, and risers are the vertical surfaces that connect treads. The edge of a tread or landing that projects over the riser is called a nosing or leading edge. Handrails are the horizontal or sloping rail above stairs that intended for grasping or support.
According to the IRC, the minimum tread depth must be 10 inches as measured horizontally on the flat surface of the step from one riser to the next. These measurements must be uniform throughout an entire flight of steps, varying by no more than 0.375 inches. Nosings, the overhanging portion, must be curved with a radius under 0.56 inches. If the risers are solid, the nosing must project between 0.75 and 1.25 inches, and must be uniform between two stories, with variations of less than 0.375 inches. This applies to nosings on treads and landings. Beveling on noses must be less than 0.5 inches.
Nosings are not needed if the tread depth is 11 inches or greater.Standards may also be modified or ignored on bulkhead enclosure stairways that meet certain conditions. These are structures that connect an outside grade level such as a garden to a lower finished level such as a basement. They must not be the only required exit from a building. They must have a maximum height of 8 feet as measured from the finished lower level to the grade level. And a hinged door or other approved means must cover the opening from the outside grade level to the top of the stairway.