In a home, stairs are the most useful way of traveling between floors, but only if they remain durable and safe for individuals of all ages and sizes. Local building codes ensure these factors by specifying standards for all construction, including stairs and their parts, such as treads. These codes are based on the International Residential Code, or IRC, maintained by the International Code Council.
The tread is the horizontal part of a stair step where individuals place their feet when climbing stairs. The depth of the tread, also less commonly known as the tread run, must be a minimum of 10 inches. The IRC specifies measuring this depth horizontally from the foremost projections of adjacent treads and at a right angle to the tread’s front edge. Tread depths must be consistent throughout an entire flight of stairs. Only variations of 0.375 inches or less are allowed.
The risers refer to the vertical increase in height between treads. The IRC specifies a maximum riser height of 7.75 inches as measured between leading edges of adjacent treads. As with treads, risers must be uniform across an entire flight of stairs, with variations of under 0.375 inches. A riser may slope from the underside edge of a tread, as long as the angle is less than 30 degrees from the vertical. Risers may be solid, open or have a pattern, as long as the spaces within do not allow a 4-inch-diameter sphere to pass. This prevents small children from pushing their head into those spaces and getting stuck.
Spiral staircases take up to half the room of a standard incline stairway and work for small spaces. They require a minimum depth of 7.5 inches, as measured at a foot from the narrower edge of the tread. The maximum rise must be 9.5 inches. Unless otherwise specified, spiral staircases must follow the standards set for all staircases. For example, spirals must also have uniform depths and riser measurements across the entire flight of steps.
Bulkhead stairways provide access from an outside grade such as a garden to a finished lower level such as a basement. If they meet the following requirements, they are exempt from the standards for tread rise and runs required for other stairs. They must not be the only way to exit the lower space. For example, the home has a separate interior staircase to the basement. The maximum height from the basement level to the adjacent grade must be 8 feet or under. And the opening from the grade level to the stairway must be covered by an enclosure such as hinged doors.
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