Stairway Code Requirements - An Overview1/25/2023 18 Comments 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.
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: 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:
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 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 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.
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. 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: For IBC Stairways: Need assistance on your specific project? Add Campbell Code Consulting to your team. They are a full-service code consulting and fire protection engineering firm that can help you navigate complex code challenges. 18 Comments Chris Campbell 2/5/2023 02:57:00 pm Hi Aaron, These images are intended to be a snapshopt of the middle of the stairway...the bottom of the stairs, including the handrail returns, are not shown. Reply David Goodman 2/17/2023 10:15:15 am For IBC if the stairs are only required to be 36", is that the space between the handrails or the width of the tread? Also, what if the job is only replacing out of code handrails, no other modifications to the stair tower. The current stairs wouldn't meet todays codes, the handrails are very low and have 20+ inch gaps between rails. They just want to install new handrails at the tight height and with a less than 4' opening Reply david wise 5/16/2023 04:58:28 pm I believe the head height dimension is shown incorrectly on both drawings. It should measure to the top of the riser and not to the bottom of the riser. Reply Margo 9/12/2023 08:55:03 am Nice explanation with clear pictures. What about where one side of the stairway is halfway open is a railing or blocking of the stairway and open space required? Thank you for the website and discussions. Reply Joe Didonato 9/17/2023 02:23:34 pm 2015 IRC Code I can not find specific exemptions in the 2015 IRC that address these exceptions. Regards, Reply Joe Didonato 11/9/2023 10:56:26 am With no specific reference in the code to the design of a Bulkhead or Dog House stair to the basem*nt from the exterior, am I too assume that their is no requirements to these stirs? Reply 10/2/2023 11:33:09 pm Wow, I never thought about this subject in the way you presented it. Your unique take adds a new dimension to the conversation, and I'm excited to delve deeper into this topic now regarding stairway code requirements. Thanks for sharing. Reply Dan 11/9/2023 09:55:37 am For a steel pan stair, is the 44" width between the stringers or the stairway itself? Reply Luke 11/22/2023 12:01:18 pm Minimum width requirements would be the "stairway itself" think of it as the minimum tread width rather than minimum stairway width. If your stringers have a 44" space between the inside faces but you provide treads that are only 40" wide you would be non-compliant with code. Reply Margi Prueitt 12/7/2023 10:47:09 pm Is there any requirement or standard practice for marking the edge of a step in in a contrasting color or material? A stairwell in a building I use frequently has all gray rubber-type steps where the solid color causes the edges of the steps to "disappear". I believe this is a safety issue but the facility seems unconcerned. Reply 1/24/2024 09:32:32 am This breakdown of stairway regulations under the IRC and IBC is valuable. The explanation of minimum widths, handrail specifications, and exceptions provides a clear guide for those working on multi-story building projects. Reply John Hastings 2/26/2024 12:44:30 pm I am so a custom to seeing Architectural drawing details using a 11" run with a 1" nosing that it has become the norm for me. Just recently I was reviewing with our Estimator a detail of an 11 inch tread without a nosing and I questioned the design. So today I am working on an industrial stair with an 11" run. So I posed this question to my Boss: Do I increase the tread depth to 12" to cover a nosing when our estimate is based on a quote for 11" tread depth. He asked if was required? Thank you for the information on the requirement for a nosing. John Reply Tread depth includes nosing or no nosing on 11” minimum stair tread depth. I wouldn’t go around adding extra inches but you should consult through proper channels architect, building contractor/ possibly owner. Im no specialist in each individual state or if other states may vary much from the IRC on stairs. If it says 11” no nosing I would question to see if it’s correct then if that’s the intentional design be like okay but if you have to redo the work on a new set of stringers after it’s going to cost more in material and labor to redo it. Reply Bob D 4/19/2024 11:41:15 pm This is really helpful information. Is there anything in the IBC related to tread depth uniformity from step to step? Thanks. Reply Dan G 4/29/2024 04:47:02 pm Where do you find the exceptions to the 36" minimum width in the IRC? I'm not finding those exceptions. Reply | Interested in Sponsoring? CategoriesAll RSS Feed ArchivesDecember 2023 |
Stairway Code Requirements - An Overview (2024)
Table of Contents
Stairway Code Requirements - An Overview
What is a Stairway?
Minimum Width for IRC Stairways (R311.7)
Minimum Width for IBC Stairways (1011.2)
Handrail Height
Stair Treads and Risers (R311.7.5)
Stair Treads and Risers (1011.5.2)
Headroom Requirements
Vertical Stairway Rise
Summary
Categories
Archives
References
References
- https://www.jacksonwoodturners.co.uk/planning-advice/height-staircase-handrail
- https://www.thespruce.com/stair-handrail-and-guard-code-1822015
- https://www.buildingcode.blog/blog/stairwaycoderequirements
- https://homeinspectorsecrets.com/carpentry/stairs/residential-stair-handrail-irc-code/
- https://buildingcodetrainer.com/residential-stair-code/
- https://www.thespruce.com/stair-handrail-and-guard-code-1822015#:N?^T?Z\?L??Z[[??L???[ L??IL???L?\??L?[?L??܉L??[??][ۜ?L????IL?IL?[??Z[ L??L?IL??X\?
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