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Calculating egress stairways and other egress components, sprinkler system

M

MeganMcNC

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Dec 30, 2024
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5
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North Carolina
Working on a plan for a full-floor office tenant (~24k SF). Pretty typical user and with a full floor office space they want/need a larger conference room and break room (larger than 50 occupants). The two rooms are about 1,000 SF each, nothing too huge. The issue I am running into is when I run the occupant load for the floor (A-3 15/SF pp in the two larger assembly areas and B everywhere else 100 SF/pp), the occupant load is exceeding the allowed width of the existing stair (and door) widths per 1005.3.1 and 1005.3.2 in NC Building Code.
However, I think I may be grammatically reading the code incorrectly.
Does the exception mean that if the building has a sprinkler system according to Section 903.3.1.1 alone, then we can use the larger capacity calc?
And then there is another option if it has a sprinkler system according to 903.3.1.2 AND a voice alarm system that is another way to use the larger capacity calc? Basically trying to make sure if the sprinkler system is per 903.3.1.1 (more robust than the other sprinkler system noted) it doesn't have to also have the voice alarm system to use the exception calc.
I feel like there should be a comma somewhere in there to help clarify what part of the sentence the 903.3.1.2 belongs to :)
4 story building, Type IB, sprinklered NFPA 13, Wet, Fire Alarm system.

NC Code reference:
1005.3.1 Stairways. The capacity, in inches, of means of egress stairways shall be calculated by multiplying the occupant load served by such stairways by a means of egress capacity factor of 0.3 inch (7.6 mm) per occupant. Where stairways serve more than one story, only the occupant load of each story considered individually shall be used in calculating the required capacity of the stairways serving that story.
Exceptions: 1. For other than Group H and I-2 occupancies, the capacity, in inches, of means of egress stairways shall be calculated by multiplying the occupant load served by such stairways by a means of egress capacity factor of 0.2 inch (5.1 mm) per occupant in buildings equipped throughout with an automatic sprinkler system installed in accordance with Section 903.3.1.1 or 903.3.1.2 and an emergency voice/alarm communication system in accordance with Section 907.5.2.2.
 
Read footnote ‘b’ of Table 1004.1.2. You will find your salvation there.
 
RLGA said:
However, to answer your specific question, the emergency voice/alarm communication system is required with both types of sprinkler systems.
Click to expand...
RLGA said:
Read footnote ‘b’ of Table 1004.1.2. You will find your salvation there.
Click to expand...
We do use this footnote most of the time, but when it references 303.1.2 it specifically says that is for rooms that are less than 750 sf or fewer the 50 occupants. The room in this scenario are neither, so I didn't think they would count for this?
 
Chase it through performance compliance in the IEBC?

Other than that, I don't think I have any legit way of making it work without some bend on the AHJ part....
 
According to UpCodes, North Carolina is still on a 2018 state building code that's based on the 2015 IBC. With the 2021 IBC, the ICC changed the area ratio for Business from 100 s.f. per person to 150 s.f. per person. Can you get a modification to calculate the B occupant load using the 150 s.f./person ratio?
 
Yankee Chronicler said:
According to UpCodes, North Carolina is still on a 2018 state building code that's based on the 2015 IBC. With the 2021 IBC, the ICC changed the area ratio for Business from 100 s.f. per person to 150 s.f. per person. Can you get a modification to calculate the B occupant load using the 150 s.f./person ratio?
Click to expand...
Good thinking....offset the A with the B....

Or if you or the AHJ will use the exception for wiggle room:

1004.5​

The number of occupants shall be computed at the rate of one occupant per unit of area as prescribed in Table 1004.5. For areas without fixed seating, the occupant load shall be not less than that number determined by dividing the floor area under consideration by the occupant load factor assigned to the function of the space as set forth in Table 1004.5. Where an intended function is not listed in Table 1004.5, the building official shall establish a function based on a listed function that most nearly resembles the intended function.

Exception: Where approved by the building official, the actual number of occupants for whom each occupied space, floor or building is designed, although less than those determined by calculation, shall be permitted to be used in the determination of the design occupant load.
 
steveray said:
Good thinking....offset the A with the B....

Or if you or the AHJ will use the exception for wiggle room:

1004.5​

The number of occupants shall be computed at the rate of one occupant per unit of area as prescribed in Table 1004.5. For areas without fixed seating, the occupant load shall be not less than that number determined by dividing the floor area under consideration by the occupant load factor assigned to the function of the space as set forth in Table 1004.5. Where an intended function is not listed in Table 1004.5, the building official shall establish a function based on a listed function that most nearly resembles the intended function.

Exception: Where approved by the building official, the actual number of occupants for whom each occupied space, floor or building is designed, although less than those determined by calculation, shall be permitted to be used in the determination of the design occupant load.
Click to expand...
I'
Yankee Chronicler said:
According to UpCodes, North Carolina is still on a 2018 state building code that's based on the 2015 IBC. With the 2021 IBC, the ICC changed the area ratio for Business from 100 s.f. per person to 150 s.f. per person. Can you get a modification to calculate the B occupant load using the 150 s.f./person ratio?
Click to expand...
Our code switches over to the NC 2024 version tomorrow, but they still haven't released it for review. I found a link to the changes, but it looks like they didn't change the Business occupant factor to 150 (though they told us this was a change being made a few months ago at a seminar). I'd be golden if I could do that. I have reached out to AHJ about options and/or what they would approve, just waiting to hear back.
 
steveray said:
Designing to the minimum strikes again......Not you Megan, but whoever did it originally.....Welcome to THE Forum....
Click to expand...
Also, something that has me wondering about my initial question even more is that I found the original building code summary/appendix B for the sister building (basically the same building, built within a year or two, adjacent--around 2007) and in the egress chart, it does show the more generous width factors (.15/.2) for the stair and doors. So still wondering if just the NFPA 13 sprinkler system provides that (without the voice/alarm). I've asked a plan reviewer for clarification. Also, will pop into the office to look at the Commentary for any clarity.
 
CT "fixes" this by saying wet or dry people are the same size, no gimmies:

1005.3.1 Stairways​

The capacity, in inches, of means of egress stairways shall be calculated by multiplying the occupant load served by such stairways by a means of egress capacity factor of 0.3 inch (7.6 mm) per occupant. Where stairways serve more than one story, only the occupant load of each story considered individually shall be used in calculating the required capacity of the stairways serving that story.

I thought about an IEBC proposal to allow +5% or something like that but I imagine it would be a fight I am not willing to have...

At least one of the architects in the audience hates our CT amendment, especially in existing buildings...
 
steveray said:
CT "fixes" this by saying wet or dry people are the same size, no gimmies:

1005.3.1 Stairways​

The capacity, in inches, of means of egress stairways shall be calculated by multiplying the occupant load served by such stairways by a means of egress capacity factor of 0.3 inch (7.6 mm) per occupant. Where stairways serve more than one story, only the occupant load of each story considered individually shall be used in calculating the required capacity of the stairways serving that story.

I thought about an IEBC proposal to allow +5% or something like that but I imagine it would be a fight I am not willing to have...

At least one of the architects in the audience hates our CT amendment, especially in existing buildings...
Click to expand...
Hey, I resemble that remark!

no joke, years ago I asked the CT State Fire Marshall we delete the sprinkler exception for stair capacity....this was his response......"We at the office of the State Fire Marshall do not believe that wet people can get out of a burning building any faster than dry people".....The same guys told me to call him Fire Marshall Bill.
 
MeganMcNC said:
Working on a plan for a full-floor office tenant (~24k SF). Pretty typical user and with a full floor office space they want/need a larger conference room and break room (larger than 50 occupants). The two rooms are about 1,000 SF each, nothing too huge. The issue I am running into is when I run the occupant load for the floor (A-3 15/SF pp in the two larger assembly areas and B everywhere else 100 SF/pp), the occupant load is exceeding the allowed width of the existing stair (and door) widths per 1005.3.1 and 1005.3.2 in NC Building Code.
However, I think I may be grammatically reading the code incorrectly.
Does the exception mean that if the building has a sprinkler system according to Section 903.3.1.1 alone, then we can use the larger capacity calc?
And then there is another option if it has a sprinkler system according to 903.3.1.2 AND a voice alarm system that is another way to use the larger capacity calc? Basically trying to make sure if the sprinkler system is per 903.3.1.1 (more robust than the other sprinkler system noted) it doesn't have to also have the voice alarm system to use the exception calc.
I feel like there should be a comma somewhere in there to help clarify what part of the sentence the 903.3.1.2 belongs to :)
4 story building, Type IB, sprinklered NFPA 13, Wet, Fire Alarm system.

NC Code reference:
1005.3.1 Stairways. The capacity, in inches, of means of egress stairways shall be calculated by multiplying the occupant load served by such stairways by a means of egress capacity factor of 0.3 inch (7.6 mm) per occupant. Where stairways serve more than one story, only the occupant load of each story considered individually shall be used in calculating the required capacity of the stairways serving that story.
Exceptions: 1. For other than Group H and I-2 occupancies, the capacity, in inches, of means of egress stairways shall be calculated by multiplying the occupant load served by such stairways by a means of egress capacity factor of 0.2 inch (5.1 mm) per occupant in buildings equipped throughout with an automatic sprinkler system installed in accordance with Section 903.3.1.1 or 903.3.1.2 and an emergency voice/alarm communication system in accordance with Section 907.5.2.2.
Click to expand...
how close is your stair capacity to your calculated occupant load? and how are you measuring the stair width?
 
Yankee Chronicler said:
According to UpCodes, North Carolina is still on a 2018 state building code that's based on the 2015 IBC. With the 2021 IBC, the ICC changed the area ratio for Business from 100 s.f. per person to 150 s.f. per person. Can you get a modification to calculate the B occupant load using the 150 s.f./person ratio?
Click to expand...
It's worth a conversation with the AHJ to see if they would consider reviewing design based on a more recent building code.
 
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