Width and Capacity (IBC 1011.2)
The number of occupants on each floor will determine the required width of the stairs. In short, the width is calculated by multiplying the occupant load served by such stairs by a factor of 0.3 inch per occupant. However, the very minimum width between handrails is 44 inches. You must calculate the IBC stair width for multi-story stairways versus single-story stairways.
Width = 0.3 x floor’s occupant load
Headroom (IBC 1011.3)
Stairways are required to have a headroom clearance of 80 inches from the edge of each stair nosing measured vertically up to the ceiling. The clearance must continue past the last step for at least one stair tread depth.
Riser Height and Tread Depth (IBC 1011.5)
The step height, also known as the riser height, must be no less than 4 inches and no greater than 7 inches. The minimum tread depth is 11 inches. If the stairs have nosings, you measure from the leading edge of the nosing to the edge of the next step’s nosing.
Uniform Dimensions (IBC 1011.5.4)
IBC stairs must have the same riser and tread dimensions throughout the stairway. The difference between the largest and smallest tread depth or riser height cannot be more than 3/8 inch.
Solid Risers (IBC 1011.5.5.3)
Solid risers are required for IBC stairs except for means of egress stairways as long as the opening between treads does not allow a 1/2 inch diameter sphere to pass through.
Landings (IBC 1011.6 & 1009.6.3)
- There must be a floor or landing at the top and bottom of each stairway.
- The width of landings must be as wide as the stairways that they serve.
- Where the stairway has a straight run, the landing does not need to be more than 48 inches deep.
- Doors opening onto a landing cannot reduce the minimum landing width to less than half.
- When the door is fully open, it cannot project more than 7 inches into the minimum dimensions of the landing.
- If a wheelchair space is required for an area of refuge, the wheelchair space cannot be located in the required minimum landing dimensions or door swing.
Stairway Rise (IBC 1011.8)
Every 12 feet of vertical rise, the stairway must have a landing.
Walking Surface (IBC 1011.7.1)
- The slope of the walking surface cannot be greater than 1:48 in any direction.
- You can have walking surfaces with openings, but the openings cannot allow a 1/2-inch diameter sphere pass through.
- If the stairs are outside, the design of the IBC stairs cannot allow water to accumulate on the walking surface.
Guards (IBC 1011.13 & 1015)
Guards are required along all open-sided walking surfaces of the stairway, including landings and stairs. The guard height must be at least 42 inches high, and it is measured vertically from the leading edges of the tread nosings or from the landing surface. Any spacing in the guards must be less than 4 inches. Shown below, the guards are vertical balusters, but guards can also be pieces of glass, wire, etc.