While working in the early phases of a project, a mechanical engineer recently asked for an estimate of the required stair pressurization system fan capacity. On this particular project, I am planning to do a CONTAM analysis, but won't start that portion until later in the Design Development phase.
Since I wanted to give the mechanical engineer an estimate for sizing purposes, I put together a quick calculator to estimate the fan size. Check it out at the link below!
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.
In the past few months, I've had several clients ask me questions regarding grade plane calculations - most often related to determining whether a particular story counts as a story above grade plane or as a basement. Here is quick rundown of how to do the calculation and the implications.
Average Grade Plane
Chapter 2 of the IBC defines Grade Plane (often referred to synonymously as Average Grade Plane) as:
A reference plane representing the average of finished ground level adjoining the building at exterior walls.
So if you have a completely flat site, the elevation where the finished ground level adjoins the building exterior walls is your grade plane. If your site is sloped, you need to take several elevations where the finished ground level adjoins the building and average them to determine the grade plane.
The most common question I receive on this: how many elevation points do you need to account for this in average?
First, the IBC does not give any specific requirements or instructions to answer this question. Your local jurisdiction could potentially have some guidance on how they want to see the calculation performed, but in my experience, most do not.
Typically, I advise clients to base the number of elevation points on the slope of the site. If you have a relatively flat site, a small number of elevation points will give you an accurate grade plane elevation. You may only need one elevation point per face of the building. On the other hand, if you have an irregular, highly-sloped site, you will need many elevation points. I once worked on a building that was built into the side of a steep hill - there we measured the elevation every 10 feet in some areas. If in doubt, the greater number of elevation points in your calculation will result in a more accurate measurement.
In the simple example above, the grade plane measurement is just the average of the elevations at the end of each wall segment (e.g. for the east wall, (280+270)/2 = 275'). However, with a more severe grade, particularly where the slope is irregular, you will need to take additional measurements, as shown in the example below.
Another common question: What if my site slopes perpendicular to the exterior walls?
The Implication - Determining a Story Above Grade Plane
Why does the grade plane calculation matter? On my projects, this always comes up when a client is trying to determine whether a particular story is actually a story above grade plane or a basement.
Chapter 2 of the IBC defines "Story Above Grade Plane" as:
Any story having its finished floor surface entirely above grade plane, or in which the finished surface of the floor next above is:
This definition has caused some confusion in the past, so here is a step by step breakdown:
There are numerous code requirements that differ between a story and a basement, but the most common one is complying with the allowable number of stories based on occupancy and construction type. I had a project this year where the floor surface of the level above was 5 feet, 10 inches above the grade plane elevation, just barely passing as a basement. 2+ inches more and the building would haven been one story taller, resulting in requirements for a more robust construction type, higher shaft ratings and substantial additional cost.
If your situation is that close, I suggest including a plan in the permit package that clearly shows the grade elevations around the building and shows your grade plane calculation. This makes it easy for plan reviewers to follow your logic and hopefully agree with your approach (remember, there are no specific IBC instructions or requirements for how to do the calculation).
What do you Think?
Have you had a project that required a detailed grade plane calculation? Have you every had a plan reviewer or code official disagree with your calculation? Let me know in the comment box!
Delayed egress doors are one of the most commonly-used features in design situations where some level of access control is needed on the path of egress. Under normal conditions, delayed-egress doors are a deterrent to building occupants, limiting access through the door unless necessary for an emergency. During an emergency, the delay function will deactivate (whether upon loss of power, or sprinkler/fire alarm activation), effectively making the door a normal egress door.
Similar to the other cheatsheets I have put together, this one is motivated by numerous architect requests for clarification as to when a delayed egress door can be provided.
After a few weeks of troubleshooting, I'm proud to share a new calculator for separated, mixed occupancy buildings! You enter in the construction type, sprinkler details, occupancies and proposed areas and the calculator will kick out the allowable height area and number of stories for each occupancy. Plus, it calculates the mixed occupancy ratios and tells you the required separations between occupancies!
I'm excited to launch a new plumbing fixture count tool that really speeds up the process of determining the required number of plumbing fixtures per IBC Chapter 29 and the IPC. Take a look here and let me know what you think!
I've also made an update to the 2015 IBC Allowable Height, Area and Stories calculator. With this update, you can now manually enter the building frontage and the calculations will update accordingly. You can check out that update here:
Over the summer, I was interviewed on the Fire Code Tech podcast. The conversation ranged from performance-based design, the UMD FPE program, trends in the industry and advice for you professionals entering the FPE/Code market. If you haven't listened, check it out!
It's been a full summer here on my end, at least in one sense. While the pandemic has forced vacation cancellations and generally fewer social gatherings, work has been full steam ahead for the past few months. I've also been working on a weekly basis to help PE Roadmap clients as they study for the Fire Protection PE exam this fall. As we get towards the last remaining months before the October exam, I am looking forward to some more regular posts on the blog, which I anticipate to be a mixture of life safety tools, cheat sheets and code questions.
On another front, I've also had some recent conversations with Joe Meyer over at MeyerFire regarding our Code Calls initiative. While we are still soliciting feedback from Indiana AHJs regarding their local requirements, we are also looking for some ways to further jump start our progress. One of these is putting together a database that provides a link to State/City/County/Municipality local amendments, as well as the link to that jurisdiction's website where you can find contact information. Similar to the main Code Calls database, we are starting in Indiana and hoping to branch out from there. More on that in the coming months.
Code Question - Openings in Stairs From Normally Occupied Spaces
On a recent project, an architect I am working with received a comment stating that openings in stairways are only permitted from normally occupied spaces. I have come across this requirement before, which originates from IBC 1023.4.
While I am quite familiar with this requirement, the fact that it was brought up in this particular situation was shocking. That's because the floor in question, a basement, was designed with two exit stairs and an enclosed corridor running the length of the building and connecting the stairs. I've sketched up a simplified version of the layout below. The plan review comments indicated that the openings into the stairs were from not-normally occupied spaces and did not comply with IBC 1023.4.
If either of the stairs opened up directly into the mechanical, electrical or storage rooms, this comment would make sense to me. However, the openings into both stairs are from the corridor, which I have always considered normally occupied space. In fact, the IBC actually requires rated corridors to continue to an exit (IBC 1020.6). While the corridors in this design are not currently rated, if the code requires corridors continuity to an exit in certain situations, how could a corridor be considered not-normally occupied here?
Upon a followup conversation with the plan reviewer, the local jurisdiction has taken the position that because all of the rooms (mechanical, electrical and storage) on the floor are considered not-normally occupied, the corridor serving those rooms should be treated the same. The reviewer also cited concern that corridor could be used for storage and result in potential fire spread into the stair.
When I brought up potential solutions, it seems that rating the corridor (or providing a rated stair vestibule) would satisfy the jurisdictions concerns.
What Do You Think?
I would love to hear your thoughts on this situation. Should this corridor be considered not normally occupied? Does this design meet the intent of IBC 1023.4? Let me know in the comments section!
In recent weeks, many states have seen a sharp increase in the number of new cases of COVID-19. According to the Johns Hopkins University Coronavirus Resource Center, Arizona, Texas and Florida are seeing record numbers of new cases in the last two weeks. Many other states are seeing rising trends as well.
At the end of March, I wrote a post about the impact the COVID-19 pandemic may have on occupant load factors. Nearly four months later, I believe it's clear that the pandemic has changed the way we work and gather as a society, at least for the foreseeable future.
In response to the pandemic, nearly every state has placed restrictions on gathering and assembly spaces, typically requiring them to operate at no more than 50% of their original capacity. This 50% reduction has included airlines, restaurants, public transit systems, and casinos, just to name a few.
As I've thought more about social distancing and occupant load factors in the last few weeks, I've been considering if this percent reduction actually makes sense.
First, lets review how building or space capacities are typically determined...
For the purposes of egress, occupant load factors found in IBC Chapter 10 (and also NFPA 101 Chapter 7) are used to determine the minimum number of occupants that need to be considered when sizing the means of egress. A denser occupant load factor results in more people per unit area and a greater egress width.
But the occupant load factors found in IBC Table 1004.5 are used to determine the minimum occupant load that needs to be accommodated by the means of egress. The IBC specifically allows the occupant load to be increased beyond the number established by Table 1004.5, so long as there is sufficient egress capacity and the load does not exceed 1 occupant per 7 square feet (IBC 1004.5.1). The posting of the occupant load that you see near the main exit from restaurants, entertainment venues and other assembly occupancies is often reflective of an increased occupant load beyond Table 1004.5.
So when a State or County Government orders restaurants to operate at 50% capacity, does this automatically result in the minimum six feet of social distancing recommended by the CDC?
It all depends on how the 100% capacity number was determined. If the restaurant's (or other business's) occupant load was originally based on a denser load factor, such as 1:15 for tables and chairs seating, even a 50% reduction in capacity is unlikely to result in social distancing. It's even more unlikely if that 100% capacity was based on an increased occupant load, beyond what IBC Table 1004.5 requires.
Instead of starting with a percent reduction in capacity, it may be more effective to use occupant load factors to determine a maximum capacity for a building or space during pandemic social distancing conditions. Using the CDC guidelines, 6 feet of distance between people results in 1 person for 36 square feet (or perhaps 1 person per ~28 square feet using a 3 foot radius measurement).
Assuming occupants can be evenly distributed through the space (a potentially big assumption), this method would allow for social distancing, regardless of the posted occupant load or exit capacity of a space.
State and Local Goverments requiring a 50% reduction in capacity is a step in the right direction if the goal is to promote social distancing in public spaces. But it might not be enough.
Instead of cutting the original capacity of a space in half, it may be more effective to apply a 1:36 or 1:28 occupant load factor to the area in question and consider this the maximum permitted occupant load for that space.
What do you think? Has the 50% reduction in capacity been effective in achieving social distancing in your area? What other ways could governments help to promote social distancing?