In projects of Type II, III, IV or V construction, architects are often forced to balance the allowable area limits of lesser construction types and the added cost of higher construction types. A fire wall is an ideal solution, as it allows for the cost savings of a lower construction type while allowing the structure on either side of the fire wall to be considered independently from an allowable area standpoint.
On several recent projects, I have seen plan reviewers treat any door opening in the fire wall as a horizontal exit, even if that was not the design team’s intention. The reviewers then issued review comments regarding compliance with the horizontal exit code requirements. This has led me to the question: is an opening in a fire wall automatically a horizontal exit?
Before I get to my answer, you might be asking: why does this matter?
Horizontal exits come with several code requirements, but in the recent projects I mentioned, the plan reviewers were citing the following:
Per IBC 1026.1, a horizontal exit can provide up to one half of the total number of exits, total exit width and total egress capacity. So if the door in the fire wall is a horizontal exit, then it can not be providing more than half of the required number of exits or required exit width.If you have a single door in the fire wall and then an exit stair on either side, this is no problem. But once you have multiple doors in the fire wall, the horizontal exit can easily exceed one half of the total required exits/width.
Per IBC 1026.4, when a horizontal exit approach is used, a refuge area is required in the space on the other side of the horizontal exit. This refuge area must be large enough to accommodate the original occupant load of the space plus 3 square feet for each occupant entering into the refuge area from the horizontal exit.
Depending on the building arrangement and capacity, providing this refuge area may be a design challenge.
Standpipe Hose Connections
Per IBC 905.4.2, a standpipe hose connection is required on each side of a horizontal exit. An exception does exist if the floor areas adjacent to the horizontal exit are within 130’ of standpipe hose connection with an exit stair.
So if any door in a fire wall is a horizontal exit, each of these code requirements must be met, adding additional cost and design coordination.
Coming back to the original question:
Is an opening in a fire wall automatically a horizontal exit?
I believe the answer is no. A door opening in a fire wall can be a horizontal exit, but it is not required to be a horizonal exit.
My opinion is based on a few factors.
First, let’s look at the definition of fire wall (IBC Chapter 2):
A fire-resistance-rated wall having protected openings, which restricts the spread of fire and extends continuously from the foundation to or through the roof, with sufficient structural stability under fire conditions to allow collapse of construction on either side without collapse of the wall.”
This definition does not mention or describe a horizontal exit at all.
Similarly, we can go to IBC Chapter 5, where the general requirements for building height and area are given. Per IBC 503.1:
For the purposes of determining area limitations, height limitations and type of construction, each portion of a building separated by one or more fire walls complying with Section 706 shall be considered to be a separate building.”
This statement indicates that a fire wall creates separate buildings for the purposes of allowable height/area and construction type, but again, it does not mention or describe a horizontal exit.
Finally, if we return to the horizontal exit section of IBC Chapter 10, we see in Section 1026.2 that a horizontal exit is permitted to be provided as either a fire wall or a fire barrier. No where in this section is a fire wall required; it is just given as one of two options. I have never heard of any AHJ requiring all fire barriers to be a horizontal exit, so why would we apply that logic to fire walls?
Icing on the Cake: An ICC Committee Interpretation
I am not the first person to ask this question, and fortunately, the ICC released a committee interpretation on this same issue a few years ago.
To summarize the committee’s interpretation, fire door openings in a fire wall are not required to be considered as a horizontal exit unless the design of the egress system intends to utilize the provisions of a horizontal exit.
While you would think that the code support described above, plus an ICC committee interpretation would be sufficient to persuade any AHJ, I have still experience pushback on this issue from plan reviewers.
Despite this, I believe the intent of the code is to allow a door in a fire wall to be used as a horizontal exit, but not require it. And if the design intention is not to utilize the horizontal exit provisions, then you do not need to be concerned about the exit capacity restrictions, refuge area requirements and additional standpipe hose connections that I described previously.
Have you encountered a similar issue before? If so, please comment below and let me know.
I work on a variety of multi-family housing projects, including residential apartment buildings and senior living facilities, where each dwelling unit has its own washer and dryer. In the past, I have always seen the dryer exhaust duct routed through a wall and then into the cavity of a floor-ceiling assembly, but on a recent project, the local AHJ questioned the validity of this approach.
Code Requirements for Dryer Vent Installation
This post is a summary of the code requirements and my suggestions for the most straight-forward way to handle the situation. All code references are the 2021 ICC Codes.
Challenge 1: No Dampers Permitted
The first challenge when approaching dryer exhaust ducts is that the International Mechanical Code (IMC) Section 504.2 specifically prohibits the installation of fire dampers or combination fire/smoke dampers.
If your dryer exhaust duct does not penetrate a rated wall or floor assembly, then you likely have no issue. However, since no one wants to look at a dryer exhaust duct running through their apartment, most designers choose to route the duct into the ceiling and then out of the building. This leads us to challenge 2.
Challenge 2: Dampers Required at Floor/Ceiling Penetrations
A duct that penetrates the ceiling of a floor/ceiling assembly and then runs horizontally through the floor cavity and out of the building would be considered a membrane penetration.
IMC Section 607.6.2 requires that duct membrane penetrations of a rated floor/ceiling or roof/ceiling assembly be protected with either a listed ceiling radiation damper or a shaft enclosure (there is a similar requirement in IBC Section 717.6.2).
We already know from our first challenge that a damper is not permitted, so that seemingly leaves a shaft enclosure as the only option. Again, it’s undesirable to building residents or designers to have a shaft enclosure simply to protect a dryer exhaust duct.
Solution: Dryer Vent Installation
Fortunately, a straight-forward solution is found in IBC 722.214.171.124, Exception 2.
The exception here allows for the omission of a damper at the ceiling membrane penetration when the duct is protected in accordance with IBC Section 714.5.2, is located within the cavity of a wall and does not pass through another dwelling unit or tenant space.
Our situation meets the last two requirements, as the duct is first routed into a wall prior to running through the ceiling cavity, where it then is routed horizontally to the exterior, without passing through another dwelling unit. For the first requirement, IBC Section 714.5.2 states that membrane penetrations of horizontal assemblies must comply with 7126.96.36.199 or 7188.8.131.52, which give requirements for through-penetration firestop systems. This section also offers 8 different exceptions.
Before we get into those exceptions, though, it’s important to point out that running the dryer exhaust duct through a wall and into the ceiling cavity presents us with another code question: how do we address the intersection of the wall and rated floor/ceiling assembly?
If the top of the wall is located completely below the ceiling membrane of the rated floor/ceiling or roof/ceiling assembly, there is no issue. However, this arrangement is difficult to construct, particularly in wood construction, as it would require a continuous ceiling running past the top of the wall.
Most of the time, the top of the wall interrupts the ceiling membrane, meaning the ceiling stops on one side of the wall and continues on the other side. This arrangement would itself be considered a membrane penetration of the floor-ceiling or roof-ceiling assembly, even without a dryer duct present. IBC Section 714.5.2 Exception 7 addresses this exact situation:
The ceiling membrane of a maximum 2-hour fire-resistance-rated horizontal assembly is permitted to be interrupted with the double wood top plate of a wall assembly that is sheathed with Type X gypsum wallboard, provided that all penetrating items through the double top plates are protected in accordance with Section 7184.108.40.206 or 7220.127.116.11 and the ceiling membrane is tight to the top plates.”
This exception allows for the wall to interrupt the ceiling membrane as long as it is provided with a double wood top-plate that is tight to the ceiling and sheathed with Type X gypsum board. Note that this section does not require the wall to be rated.
Additionally, the exception requires that the duct be protected in accordance with Section 718.104.22.168 or 722.214.171.124 (the same through penetration firestop sections referenced earlier).
For my specific project, the building is a wood-framed structure, so there was no issue in providing a double top plate for each wall. In buildings of Type I or II construction, this would still be a valid approach as long as the wall itself is not a bearing wall and fire-retardant treated wood is used for the double top plate (IBC Section 603.1, Item 1.1).
The final code section here, IBC Section 7126.96.36.199, requires an approved through penetration firestop system with F and T ratings of at least 1 hour but not less than the rating of the floor itself. Exception 1 of this section eliminates the requirement for the T rating when the penetration is located within the cavity of a wall.
This requirement forces us to find a listed fire-stop assembly that matches out proposed conditions. There are numerous assemblies available, particularly through companies such as Hilti or 3M.
If you are tracking the code path through the mechanical code, the path is shorter, but the end result is the same. IMC Section 607.6.2, Exception 2 allows for the omission of a damper at the ceiling membrane penetration when the duct is protected in accordance with IBC Section 7188.8.131.52, is located within the cavity of a wall and does not pass through another dwelling unit or tenant space. Note the subtle difference in section here compared to IBC Section 7184.108.40.206 Exception 2 – the IMC takes you directly to the through penetration firestop requirement.
See the flow chart below comparing the code path through both the IBC and IMC.
Potential Challenge with Firestop System
On the recent project where this issue came up, every firestop assembly for this configuration that I found stated that the dryer duct could be located within a wall, but when the wall was used, it had to be a minimum 1-hour rated wall. This was a challenge because the proposed configuration for my project involved the dryer exhaust duct running through an interior dwelling unit wall which was not rated.
After a few hours of digging through the UL firestop database, I could not find a single listed firestop system that described a duct running through a non-rated wall and then into a 1-hour floor/ceiling assembly. This was a surprising result, as the IBC clearly does not require the wall to be rated when using Section 714.5.2 Exception 7. I ended up pursuing an Engineering Judgment to address the situation.
Both the IBC and IMC provide code paths to route a dryer exhaust duct through wall, into a rated floor/ceiling or roof/ceiling assembly, and then out of the building. A listed firestop assembly is required to address the penetration of the duct through the ceiling membrane. If you happen to be running your duct through a rated wall, there are numerous firestop assemblies readily available for this configuration. If you are running the duct through a non-rated wall, you will likely need an engineering judgement. If you have found a listed firestop assembly that allows for a non-rated wall in this scenario, please let me know!
After a really nice response on the fire and smoke damper cheatsheet I have created a questionnaire tool that makes the process way easier. You answer a series of yes/no questions and the tool kicks out the damper requirement and code reference! Enter your info below to checkout the tool...
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.
If you are located in any major city, it’s likely that you can take a short walk down the street and find an instance of two adjacent buildings built up next to each other. If you’re out in the suburbs, you have probably seen this situation in the form of a row of townhouses. In the U.S., and other countries that adopt the International Building Code (IBC), these abutting buildings likely fall into one of the following cases:
In either case, the IBC recognizes three distinct approaches for the wall(s) located between the abutting buildings. All references are to the 2015 IBC.
Walls Between Abutting Buildings
Abutting Exterior Walls
In both cases described above, the IBC allows for two abutting exterior walls to separate the two buildings. Since the two buildings have a zero fire separation distance, IBC 602 requires both walls to have a 1-hour fire-resistance rating for most occupancies (the requirement is higher for Groups M, F-1, S-1 and H). Similarly, IBC 705.8 prohibits openings in either of these walls.
Since both structures are considered separate and distinct buildings, structural independence is required. Both exterior walls are prohibited from bearing on each other, and the walls must be supported and braced by their respective buildings. This strategy is common when the two buildings have tenants or occupants who are unrelated to one another. Since openings between the buildings are not permitted, this approach is not practical when doors between buildings are required.
Once common exception is a concrete parking structure that is surrounded on all sides by a residential building. This type of project, often referred to as a “wrapper building” or “Texas Donut," utilizes a newly-added provision in the 2015 IBC 705.3, which allows protected openings between the buildings, as long as the opening in the parking garage building has a 1.5-hour fire resistance rating. The opening in the residential building does not require an opening protective in this case.
Fire walls are required to be structurally independent from the building and must be continuous to the foundation. For two abutting buildings located on the same lot, this means that neither of the buildings can bear on the fire wall, which often results in the construction of three walls: the fire wall plus a separate exterior wall for each building. Floor assemblies can be connected to the fire wall using breakaway clips for continuity purposes, but they cannot be supported by the fire wall.
While the structural requirements for a fire wall are more restrictive than for exterior walls located near a lot line, fire walls are permitted to have protected openings. The openings in fire wall are limited to 156 SF, unless both buildings on either side of the fire wall are fully sprinkler-protected, in which case there is no limit to the area of openings (IBC 706.8). The required fire resistance rating of a fire wall is dependent on the occupancy classifications involved (IBC Table 706.4).
Beginning in the 2015 IBC, code language was added to allow for compliance with NFPA 221 to satisfy the requirements of IBC 706. NFPA 221 contains provisions to allow double fire walls (two rated walls built next to each other) in lieu of one structurally independent fire wall. As shown in NFPA 221 Table 4.5 (copied below), two walls, each with a 2-hour fire resistance rating are deemed equivalent to a single 3-hour fire wall.
This is similar to the abutting exterior wall strategy described previously, but the required wall rating is increased in order to meet the NFPA 221 requirements. Though this approach involves two separate walls, the entire assembly is considered a fire wall by the IBC. The fire wall strategy is best suited when there is a single owner or tenant in both buildings and openings between the two buildings are necessary.
The final option described in the IBC for the wall between two abutting buildings is a party wall. A party wall is described in the IBC as “Any wall located on a lot line between adjacent buildings, which is used or adapted for joint service between the two buildings…” (IBC 706.1.1).
This description indicates that party walls are specific to abutting buildings located on separate lots; a wall between buildings on the same lot would not be considered a party wall. Party walls must meet all of the requirements for fire walls, except that no openings are permitted. Generally, party walls require both owners to agree on how the wall will be used and any future design changes will be handled.
Abutting buildings can be found on the same lot or on two adjacent lots. Architects and engineers can choose between: (1) two abutting exterior walls, (2) a fire wall, or (3) a party wall when designing the wall between the two buildings. How have you approached designs in this situation? Comment and let us know!