Stairways | CRC § R311.7
Stairways are often overlooked, but the codes governing their construction are crucial for ensuring safety and accessibility.
Let's first unpack some of the terminology:
- Stairways: A series of steps, or flight of stairs, connecting different levels in a building. It is defined in the CRC as "One or more flights of stairs, either interior or exterior, with the necessary landings and connecting platforms to form a continuous and uninterrupted passage from one level to another."
- Clear Width: The actual width of the stairway that is available for use, free of obstructions.
- Headroom: The vertical space above the stairway, measured from the steps to the ceiling above. Adequate headroom is important to prevent people from hitting their heads while using the stairs.
- Vertical Rise: The total vertical height that a flight of stairs ascends, from one floor level to another.
- Risers: The vertical components of a staircase that elevate each step above the previous one. It is defined in the CRC as "The vertical component of a step or stair."
- Treads: The horizontal parts of a staircase that you step on. The CBC defines it as "The horizontal part of a step."
- Nosing: The part of the tread that overhangs the riser below. The CRC defines it as "The leading edge of treads of stairs and of landings at the top of stairway flights."
- Footcandle (Lux): A measurement unit for the amount of light (illumination) on a surface. One footcandle is equivalent to one lumen per square foot, or approximately 11 lux.
These codes cover a variety of topics, from the minimum required width and maximum allowed riser height of stairways, to the specifications for tread depth and nosing projection, and even to the requirements for both interior and exterior illumination of the stairways for safety.
Stairways are required to comply with California Residential Code R311.7, except stairways not within or serving a building, porch or deck, stairways leading to uninhabitable attics, and stairways leading to crawl spaces.
Stairways shall be not less than 36 inches (914 mm) in clear width at all points above the permitted handrail height and below the required headroom height. The clear width of stairways at and below the handrail height, including treads and landings, shall be not less than 31 ½ inches (787 mm) where a handrail is installed on one side and 27 inches (698 mm) where handrails are installed on both sides.
The headroom in stairways shall be not less than 6 feet 8 inches (2032 mm) measured vertically from the sloped line adjoining the tread nosing or from the floor surface of the landing or platform on that portion of the stairway.
A flight of stairs shall not have a vertical rise greater than 12 feet 7 inches (3835 mm) between floor levels or landings.
The riser height shall be not more than 7 ¾ inches (196 mm). The riser height shall be measured vertically between leading edges of the adjacent treads. The greatest riser height within any flight of stairs shall not exceed the smallest by more than 4 3/8 inch (9.5 mm). Risers shall be vertical or sloped from the underside of the nosing of the tread above at an angle not more than 30 degrees (0.51 rad) from the vertical. At open risers, openings located more than 30 inches (762 mm), as measured vertically, to the floor or grade below shall not permit the passage of a 4-inch-diameter (102 mm) sphere.
- The opening between adjacent treads is not limited on spiral stairways.
- The riser height of spiral stairways shall be in accordance with Section R318.104.22.168.
The tread depth shall be not less than 10 inches (254 mm). The tread depth shall be measured horizontally between the vertical planes of the foremost projection of adjacent treads and at a right angle to the tread's leading edge. The greatest tread depth within any flight of stairs shall not exceed the smallest by more than 3/8 inch (9.5 mm).
Nosings at treads, landings and floors of stairways shall have a radius of curvature at the nosing not greater than 9/16 inch (14 mm) or a bevel not greater than 1/2 inch (12.7 mm). A nosing projection not less than 3/4 inch (19 mm) and not more than 11/4 inches (32 mm) shall be provided on stairways. The greatest nosing projection shall not exceed the smallest nosing projection by more than 3/8 inch (9.5 mm) within a stairway.
Interior stairways shall be provided with an artificial light source to illuminate the landings and treads. The light source shall be capable of illuminating treads and landings to levels of not less than 1 footcandle (11 lux) as measured at the center of treads and landings. There shall be a wall switch at each floor level to control the light source where the stairway has six or more risers.
- A switch is not required where remote, central or automatic control of lighting is provided.
Exterior stairways shall be provided with an artificial light source located at the top landing of the stairway. Exterior stairways providing access to a basement from the outdoor grade level shall be provided with an artificial light source located at the bottom landing of the stairway.