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Key Takeaway: The IRC and IBC both provide a variety of requirements for stairways and staircases, including minimum width, minimum and maximum riser/tread dimensions, minimum headroom height and maximum total rise. A stairway is a key part of the means of egress for any multi-story building or structure. Also known as a stair or staircase, stairways provide a path for occupants to traverse from one level to another within a building or space. In this post, we’ll review some of the key requirements for stairways from both the International Residential Code (IRC) and the The International Building Code (IBC). All references are to the 2021 editions of these codes.  An interior open stairway. What is a Stairway?There are two key definitions here that are important to understand: Stair and Stairway. Both the IRC and IBC defines these terms as follows: Stair: “A change in elevation, consisting of one or more risers.” Stairway: “One or more flights of stairs, either exterior or interior, with the necessary landings and platforms connecting them, to form a continuous and uninterrupted passage from one level to another.” So a stair is simply the change in elevation that is created by one or more risers, while a stairway includes both the stairs and the required landing and platforms. Note that the term “staircase” is frequently used when referring to a stairway, but neither code actually uses this term. If you are working on a project that contains an unenclosed stairway (also known as an open stairway), be sure to check out this post on additional requirements. Minimum Width for IRC Stairways (R311.7)For projects falling under the IRC, the minimum stair width is 36 inches. The minimum width must be provided at all points above the permitted handrail height and below the required headroom height (meaning walls or other protruding objects cannot decrease this minimum width). Any provided handrails cannot protrude more than 4.5 inches into the minimum width. So if a handrail is provided on one side, the minimum clear width is 31.5 inches and if a handrail is provided on both sides, the minimum clear width is 27 inches. Note that the following stairways are not required to meet the minimum width requirements:
 Stair width and handrail requirements from the 2021 IRC. Minimum Width for IBC Stairways (1011.2)For projects falling under the IBC, there are two width requirements that apply: minimum width and required capacity. Generally, the minimum stair width is 44 inches, unless the stairway serves an occupant load of less than 50, in which case the minimum width is 36 inches. Note that if the stairway is serving as an accessible means of egress, the minimum width between handrails is 48 inches, unless the building is fully sprinkler-protected or the stairway is provided with an area of refuge. Check out this article for more information on the required means of egress vs. accessible means of egress. Note that the following stairways are not required to meet the minimum width requirements:
The second width requirement is the required egress capacity of the stairway (IBC 1005.3.1). The required capacity is determined by multiplying the occupant load using the stairway by a capacity factor of 0.3 inches per occupant. In other than Group H and Group I-2 occupancies, this factor is reduced to 0.2 inches per occupant when the building is fully sprinkler-protected and equipped with a voice fire alarm system. There are also reductions available for open-air or smoke-protected assembly seating spaces. Note that for multi-story buildings, only the occupant load of each individual story is considered when calculating the required capacity for each stair, not the cumulative occupant load using the stair. Similar to the IRC, the IBC allows handrails to project a maximum of 4.5 inches into the required width. So for a stair with handrails on each side that has a minimum required width of 44 inches, the minimum width between handrails would be 35 inches. Handrail HeightIn both the IRC and IBC, handrails are required to be located a minimum of 34 inches and a maximum of 38 inches above the stair. Specifically, this dimension is measured vertically from the stair tread nosing. Note that when handrails are transitioning between flights or at the start of a stairway, the fitting and bendings are permitted to exceed the maximum height.  Stair width and handrail requirements from the 2021 IBC. Stair Treads and Risers (R311.7.5)For projects falling under the IRC, the minimum tread depth is 10 inches, plus a required nosing of at least ¾ inch. If a tread of at least 11 inches is provided, there is no required nosing. The maximum permitted nosing is 1.25 inches. In any stairway, the tread depth and nosing depth have a maximum permitted variation of ⅜ inch. Note that under the IRC, the tread depth is 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 maximum riser height is 7.75 inches, with a similar maximum permitted variation of ⅜ inch in any single stairway. Risers must be vertical or have a maximum slope of 30 degrees from vertical.  Stair dimensional requirements from the 2021 IRC. Stair Treads and Risers (1011.5.2)For projects falling under the IBC, the minimum tread depth is 11 inches. There is no requirement to provide a nosing, but the maximum nosing projection is 1.25 inches. Note that under the IBC, the tread depth is measured horizontally between the vertical planes of the foremost projection of adjacent treads and at a right angle to the tread's nosing. The IBC requires stairs to have a minimum riser height of 4 inches and a maximum height of 7 inches. Note that the following stairways are not required to meet the minimum riser/tread requirements:
 Stair dimensional requirements from the 2021 IBC. Headroom RequirementsBoth the IRC and IBC have similar requirements for headroom clearance. In both codes, the minimum headroom clearance is 80 inches, measured vertically from a line connected to the edge of each nosing. Both codes have exceptions for spiral stairways and where the nosings of treads at the side of a flight extend under the edge of a floor opening through which the stair passes (limited to Group R-2 dwelling units and Group R-3 in the IBC). Vertical Stairway RiseUnder the IRC, a single flight of stairs can have a maximum vertical rise of 12 feet 7 inches between floor levels or landings (R311.7.3). Under the IBC,the maximum rise is 12 feet (1011.8). SummaryThe requirements for stairways depend on whether your project falls under the IRC or IBC.
For IRC Stairways: Minimum Width = 36” Maximum Handrail Projection = 4.5” each side Minimum Tread Depth = 10” Minimum Nosing = ¾” or provide 11” tread Maximum Nosing = 1.25” Maximum Riser Height = 7.75” Minimum Headroom = 6’-8” Maximum Stairway Rise = 12’-7” For IBC Stairways: Minimum Width = 44” or 36” for smaller occupant loads. See also required capacity requirements. Maximum Handrail Projection = 4.5” each side Minimum Tread Depth = 11” Minimum Nosing = Not Required Maximum Nosing = 1.25” Minimum Riser Height = 4” Maximum Riser Height = 7” Minimum Headroom = 6’-8” Maximum Stairway Rise = 12’
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Key Takeaway: Egress windows are required in all sleeping rooms for projects falling under the IRC and in many sleeping rooms for projects falling under the IBC. When required, the openings must meet specific egress window sizing requirements, and when provided below grade, must open into an area well. If you are working on a residential design or construction project, an important design consideration is the requirement for egress windows. While most people in the design community understand what you are referring to with this term, “egress windows” is not actually defined in the code. The International Building Code (IBC) and International Residential Code (IRC) both refer instead to Emergency Escape and Rescue Openings (EEROs). In this article, we’ll refer to egress windows and EEROs interchangeably, but remember that the code only defines EEROs. A window can be used to meet the EERO requirements, but doors and other openings are also an option. All references are to the 2021 IBC and IRC.  A basement emergency escape and rescue opening (egress window). What is an Egress Window?Egress Windows, or as the code calls them, EEROs, are defined in the IBC as “an operable exterior window, door or other similar device that provides for a means of escape and access for rescue in the event of an emergency. Essentially, an egress window or EERO is a way for a building occupant to escape in the event of an emergency or for a first responder or other personnel to access a building for the purposes of rescue. A fire is the obvious emergency that comes to mind, but the openings could be used for any emergency situation. When are Egress Windows Required?If you are working on a residential project in the United States, your building likely falls under one of two codes: the International Building Code or the International Residential Code. While the adoption of these codes varies by State and local jurisdiction, generally the IBC applies to apartments and larger residential facilities while the IRC applies to one and two family dwellings and townhouses. Many jurisdictions amend these codes, so be sure to check the applicable code enforced by your local authority having jurisdiction. IBC RequirementsIf your project falls under the IBC, emergency escape and rescue openings are required in the following occupancies (IBC 1031.2):
If you meet either of these conditions, then the IBC requires you to provide emergency escape and rescue openings in any basement or sleeping room below the fourth story above grade plane. There are numerous exceptions where EEROs would not be required:
IRC RequirementsIf your project falls under the IRC, Emergency Escape and Rescue Openings are required in basements, habitable attics and every sleeping room. If the basement contains more than one sleeping room, an EERO is required in each sleeping room (IRC 310.1). There are numerous exceptions where EEROs would not be required:
Egress Window Sizing RequirementsBoth the IBC and IRC have the same dimensional sizing requirements for EEROs:
 Dimensional requirements for emergency escape and rescue openings. These dimensions are required to be a result of the normal operation of the window or door - you cannot break or alter the window/door in order to achieve the required dimensions. Basement Egress WindowsArea wells are required to be a minimum of 9 square feet in area with a minimum dimension of 36 inches in both length and width. The area well must also be of sufficient size to allow the EERO to fully open. If the area well has a depth of more than 44”, a ladder or steps are required. The egress window or door opening into the area well cannot obstruct the ladder or steps when fully open.  Dimensional requirements for area wells. If you choose to provide a ladder for the area well, the ladder must have an inside width of at least 12 inches, must project at least 3 inches from the area well wall and the ladder rungs must be spaced no more than 18 inches apart for the entire height of the area well. If you choose to prove steps for the area well, the steps must have a minimum width of 12 inches, a minimum tread depth of 5 inches and a maximum riser height of 18 inches for the entire height of the area well. Finally, area wells are required to be connected to the buildings foundation drainage system unless the building is located on well-drained soil or sand-gravel mixture soils as defined by IBC 1803.5.1 and IRC 405.1 Bars, Grilles, Covers and Screens over Egress Windows When bars, grilles, covers, screens or other similar devices are placed over EEROs or area wells, these devices cannot reduce the minimum required dimensions described above. Additionally, the bar, grilles, cover or screen must be releasable or removable from the inside without a key or tool and cannot require a greater force than what is required to open the EERO itself. SummaryEgress windows, which the code refers to as “Emergency Escape and Rescue Openings” (EEROs) are required in all sleeping rooms for projects falling under the IRC and in many sleeping rooms for projects falling under the IBC.
When required, EEROs must meet the following size requirements:
If the EERO is below grade level, a minimum 36” x 36” area well is required. If the area well is more than 44” deep, a ladder or steps are required. |
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