Your handrails need to be on both sides of the stair and can’t project more than 4.5″ into the stair width on each side. 37. The Ontario Building Code | Stair Width 9.8.2.1. International Building Code for Stair treads and risers. Open risers are not permitted. 42˝ Min. It important to note that the ADA will require you to go one tread depth plus 12″ past the bottom riser so it generally overrides the IBC. See Section 1009.3 for accessible means of egress stairways. Exceptions: Stairways serving an occupant load of less than 50 shall have a width of not less than 36 inches. The minimum width for stairways shall not be less than 36 inches clear. In order to determine this the code refers us to Section 1005.1, but before we look at this section the code does say that the minimum width shall not be less than 44 inches. As for rectangular stair treads the depth should not be less than 11 inches when measured horizontally between the vertical plane of the foremost projection of the adjacent tread and at a right angle to the tread’s nosing. If the stairway serves a floor with an occupant load of less than 50, the minimum clear width is reduced to 36″.Â, Example: calculating multi-story stair width, Example: calculating single-story stair width. 1005.3.1 Stairways  The capacity, in inches, of means of egress stairways shall be calculated by multiplying the occupant load served by such stairways by a means of egress capacity factor of 0.3 inch per occupant. Exception 1 in Section 1005.3.1 allows for a reduction in size when a building is equipped with an automatic fire sprinkler system and an emergency voice/alarm communication system, except for when serving an occupancy group H and I-2. The International Residential Code (IRC) and the International Building Code (IBC) provides the staircase railings codes and guidelines in the United States. The minimum recommended stair width is between 34" and 36" across. Keep in mind, the minimum clear width is typically 44″, but it is sometimes reduced to 36″ for low-capacity floors. Reference the IBC codes below to check your work. Handrailings will protrude into and may reduce the nominal the stairwell width. 1:48. Exceptions: For other than Group H and I-2 occupancies, the capacity, in inches, of means of egress stairways shall be calculated by multiplying the occupant load served by such stairways by a means of egress capacity factor of 0.2 inch per occupant in buildings equipped throughout with an automatic sprinkler system installed in accordance with Section 903.3.1.1 or 903.3.1.2 and an emergency voice/alarm communication system in accordance with Section 907.5.2.2. Inconsistencies or variations in risers or treads could interfere with the rhythm of the individual using the stairs. Handrailings reduce the nominal stairwell width. Edges shall have a minimum radius of 0.01 inch (0.25 mm). A prime example is the standard stair width. 1005.5 Distribution of Minimum Width and Required Capacity Where more than one exit, or access to more than one exit, is required, the means of egress shall be configured such that the loss of any one exit, or access to one exit, shall not reduce the available capacity or width to less than 50 percent of the required capacity or width. On any given flight of stairs, all steps shall have uniform riser heights and uniform tread widths. The diameter of the staircase determines the width of the stair treads, the minimum dimension of which is specified by the IRC. Calculating the IBC stair width can be complicated because it is determined by the building’s occupant load, so we have put together this simplified version of the IBC codes. In order to access a 12-foot-high platform, an IBC stair would need 21 steps (7-inch rise, 11-inch tread), making the entire horizontal run of the stairs 19.25 feet. Minimum width for stairways is determined by using a factor of 0.3 inch per occupant for non-sprinklered buildings or a factor of 0.2 inch per occupant for buildings equip with sprinklers and alarms, but shall at no point be less than 44 inches. Exception 1 in Section 1011.2 allows for a width of not less than 36 inches when a stairway is serving an occupant load of less than 50. There’s an exception to that. IF there is a compliant sprinkler system installed throughout the building, multiply the occupant loads by 0.2, not 0.3. PHOTO 1. Stair Width (1) Except as provided in Sentence (2), required exit stairs and public stairs serving buildings of residential occupancy shall have a width, measured between wall faces or guards, of not less than 900 mm. Factor per Section 1005.3.1 is 0.3 inch per occupant. If the distance between floor levels exceed 12 feet, the flight of stairs would require a level landing somewhere in-between to break up the flight of stairs. Take the largest width that you calculate, and use it for the entire stairway system. The width must continue up to the minimum headroom of 80 inches above the tread or landing surface. 311.7.4.2 – Minimum Tread Depth is 10” (max .
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