In the A/E design community, the term "open stair" is frequently used to describe a stair that is not enclosed with walls, partitions or barriers. While "open stair" is not a term used in the International Building Code, it generally aligns with a stairway (which is a defined term in the IBC) not used for egress purposes or an exit access stairway (also a defined term). The terms "communicating stair" and "convenience stair" are also used in the same line of discussion, though depending on the situation, these could be referring to communicating spaces or convenience openings, both types of vertical openings defined in NFPA 101.
In this post, we'll review the IBC requirements for open stairs and describe several code paths that can be used to provide open stairs in your design. I will use the term "open stair" throughout the post, but remember, since this is not a defined term, any formal documentation on drawings, plans etc. should use the proper nomenclature identified in this overview. This post will be limited to stairs within a building and will not address exterior stairways.
Open Stairs - 2018 IBC Code Paths
Stairway Connecting Levels within a Story
The first and most simple type of open stair connects one or more levels within a single story. This stair could be provided to access a raised floor area or a mezzanine, or to access areas on a story that are at different elevations due to a sloping site.
If the open stair is not used as part of the means of egress, the IBC would view it as simply a "stairway." If it is on the path of egress, it then becomes an exit access stairway. In either case, since this type of stair does not connect multiple stories, there is no code requirement to enclose the stairway or provide a rated separation (IBC 1019.2).
One other important point for this type of open stair is the requirement for accessible means of egress (IBC 1009). An exit access stair connecting levels on the same story is not permitted to be part of an accessible means of egress, unless the stair is providing the means of egress from a mezzanine (IBC 1009.3.1). If you are not sure how to address required vs. accessible means of egress requirements, check out this post for more details.
Stairway Connecting Two Stories
If your open stair does connect two stories, a few additional requirements are triggered. First, IBC 712.1.9 gives a number of requirements for vertical two-story openings. These include:
If your open stair is part of the means of egress (exit access stairway), IBC 1019.3 gives similar requirements. Note that open stairs connecting two stories are not permitted in Group I-2 and I-3 occupancies.
Stairway Connecting Three or More Stories
If your open stair connects three or more stories, the most common approach is to use a draft curtain and closely spaced sprinklers per IBC 1019.3.4. Use of this provision requires the following:
In Group B and M occupancies, there is no limit to the number of stories that can be connected with this approach. In all other occupancies, this is limited to four connected stories, except Groups I-2 and I-3, where it is not permitted at all.
Open Stairs in Group R Occupancies
In Group R-1, R-2 and R-3 occupancies, open stairs up to four stories are permitted if they are contained within a single dwelling unit, sleeping unit or live/work unit.
Open stairs are also permitted in Group R-3 congregate living facilities and Group R-4 occupancies.
Open Stairs within an Atrium
If located within an atrium, open stairs are permitted with no limit to the number of stories connected. Keep in mind that atriums have a host of additional requirements in the code, such as smoke control and rated separation from other building spaces. Open stairs in an atrium are permitted to serve as exit access stairways, though the travel distance when using such stairs is limited to 200 feet (IBC 404.9.3).
There are a few other situations where the code allows open stairs without any rated enclosure or separation:
There are many cases where the IBC allows open stairs. When open stairs are used as part of the means of egress for a building, they are considered "exit access stairways." Otherwise, they would fall under the "stairway" definition in the code. If your project is required to comply with NFPA 101, be sure to check out Chapter 8, which has more stringent requirements for vertical openings than the IBC.