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Room occupant load calculations: round up or down?

Tim Mailloux said:
we typically have under 20sf of casework in a classroom, i thin the average is about 16sf.
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The folks I work for almost never do any classroom larger than 950. Fact is, regardless of code requirements per sq ft, state requirements of teacher to student ratios have the numbers much lower. It's actually better to design smaller classrooms and add other SGI or learning support rooms with the "leftover" sq ft available. When designing those larger classrooms if the building design makes them more of a narrow rectangle than a square the separation distance of the 2nd exit becomes a problem and add to that door swing,panic hardware,and lighted exit signs and it's way not worth the bang for the buck so to speak.
 
If it is a code requirement to assign an occupant load to each private office, what does 150 gross (as compared to net) mean?
 
I wonder if some plan reviewers are lazy and just want to add up the number of occupants listed for each space that an egress element serves instead of adding up the area served and dividing by the SF per occupant.

BTW, if an occupancy is based on gross area shouldn't you be required to list the number of occupants for each corridor, restroom, closet, etc?
 
Paul Sweet said:
I wonder if some plan reviewers are lazy and just want to add up the number of occupants listed for each space that an egress element serves instead of adding up the area served and dividing by the SF per occupant.
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FIFY.....I wonder if some designers are lazy and just don't want to show how their egress element serves each space as a system in accordance with 107.2.3

We all have different perspectives, but we can discuss and come to some agreement.....Typically.....Unless the designer insists on being wrong anyway.....
 
JPohling said:
For you round down folks what is your occupant load for a private office less than 150 SF? zero? No
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I understand everyone logic for rounding up, I have always done it that way because thats what everyone has done. But IMO that not what the actual code text says.
......The number of occupants shall be computed at the rate of one occupant per unit of area as prescribed in Table 1004.5.....

The code language is clear that we are dealing with whole occupants and whole units of area when determining occupant loads. Until you reach an whole unit of area (that ever that is based on the room or space), an occupant doesn't get assigned to that space.

Other than the old stand by "that's what we have always done" and using the actual code text, convince me I am wrong.
 
Although I’ve typically rounded up, I don’t see what’s wrong with using fractional occupant loads for an individual room when they’re going to be added into a total. There are many cases where the occupant load factor doesn’t actually predict the number of occupants. Take apartments as an example. A floor of a typical 4-story apartment building with maybe 75 apartments on a floor have could have an occupant load of something like 350-400 and have maybe 100-125 residents.
 
Tim Mailloux said:
small office spaces that are supposed to lumped together in one large gross calculation, not many small individual calculations.
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Are we talking net or gross? ......And depending on how you read 107.2.3.....And for the record I would support the fractional summing from Jay Smith in post #57

Office/ lump/ gross might be a bad example....
Shops and other vocational room areas
[td]
50 net​
[/td]​
Lets say you have a 7X7 machine room in a voc space....Is that 1 or none? I agree that the singular net areas are so small the likelyhood of a "less than" is far less than the amount of times you would round up but.....

[A] 107.2.3 Means of Egress​


The construction documents shall show in sufficient detail the location, construction, size and character of all portions of the means of egress including the path of the exit discharge to the public way in compliance with the provisions of this code. In other than occupancies in Groups R-2, R-3, and I-1, the construction documents shall designate the number of occupants to be accommodated on every floor, and in all rooms and spaces.

And to be fair, I have rarely seen a designer spec the capacity/ people accommodated of a corridor on a plan....Even less so add the people as required by gross....Even more complicated in mixed use.....
 
Jay Smith said:
If it is a code requirement to assign an occupant load to each private office, what does 150 gross (as compared to net) mean?
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There is a definitions chapter that defines those terms...

Paul Sweet said:
I wonder if some plan reviewers are lazy and just want to add up the number of occupants listed for each space that an egress element serves instead of adding up the area served and dividing by the SF per occupant.

BTW, if an occupancy is based on gross area shouldn't you be required to list the number of occupants for each corridor, restroom, closet, etc?
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Yes?

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You know what, I'm going to design a 1,000,000 SF office building stuff full of 60 SF offices. It will be great, because I can round each office DOWN to 0, it will have an occupancy of 0!

The building won't even need an entrance or exit!
 
Penguin87 said:
There is a definitions chapter that defines those terms...
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Yes, but the usage in this thread doesn’t match my understanding of those definitions. I understood gross to be calculated like this image. I’ve never seen this approach rejected.
 

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Jay Smith said:
Yes, but the usage in this thread doesn’t match my understanding of those definitions. I understood gross to be calculated like this image. I’ve never seen this approach rejected.
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my understanding of gross occupant load calculations for egress is the same, and is consistent with the code commentary and code illustrated books.
 
As one of your token Canucks, I delved into this from the north-of-the-border perspective. Nothing I could find in the Codes, or in the guides, state what to do with occupant load; however, the NFPA has a fact sheet that directs folks to calculate occupant by rounding up.
 
Jay Smith said:
Yes, but the usage in this thread doesn’t match my understanding of those definitions. I understood gross to be calculated like this image. I’ve never seen this approach rejected.
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My plans have been rejected on multiple occasions when I've tried that method. At least in the jurisitication I work, the definition of "space" is interoperated as a definable space, such as a room (California added a definition for the word "space" in their codes, but I don't see how their definition conflicts with IBC). A room is a space by definition, therefore each room, gross or net, should be calculated independently, rounded up, then added. For gross load factors, measure to the center of the wall so that the thickness is accounted for. That's how a few Building Officials in my area have explained it to me at least.

I've can often get plans approved using the method you show in that diagram when there's a 3rd party plan review, but when it's in-house at the jurisdiction, they rarely get approved.
 
JPohling said:
For you round down folks what is your occupant load for a private office less than 150 SF? zero? No
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I don't assign occupant loads to individual offices as they are part of a larger gross occupant load calculation encompassing the whole business area which includes corridors, toilet rooms, stairs & mechanical shafts. This approach is consistent with both the IBC code commentary and IBC Code Illustrated books.
 
[BE] FLOOR AREA, GROSS. The floor area within the inside perimeter of the exterior walls of the building under consideration, exclusive of vent shafts and courts, without deduction for corridors, stairways, ramps, closets, the thickness of interior walls, columns or other features. The floor area of a building, or portion thereof, not provided with surrounding exterior walls shall be the usable area under the horizontal projection of the roof or floor above. The gross floor area shall not include shafts with no openings or interior courts.

Round up for the total OL means of egress sizing

[BE] FLOOR AREA, NET. The actual occupied area not including unoccupied accessory areas such as corridors, stairways, ramps, toilet rooms, mechanical rooms and closets.

Add all occupiable space numbers including fractions then round up for the total OL number.

The larger of the two numbers is the one you should use for means of egress sizing. You do not round up each individual room.
99% of the time the gross floor area will be the larger number.
 
And what happens when you have classrooms on one side of a corridor (20net) and offices (150 gross) on the other? How much of the corridor goes with the gross?

We need to figure out how to be reasonable.....
 
steveray said:
And what happens when you have classrooms on one side of a corridor (20net) and offices (150 gross) on the other? How much of the corridor goes with the gross?

We need to figure out how to be reasonable.....
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in that case I would assign the corridor as part of the Net classroom occupancy. Any corridors or passages with in the admin area would be included in the Admin areas gross calculation. Also and conference rooms or waiting areas in the admin area would get broken out as separate 1 per 15 or 1 per 7 assembly calculations. I have never had an AHJ (local, state or 3rd party) in CT or MA question that approach.
 
Tim Mailloux said:
in the same vein, if you have 120 individual rooms with net occupant load calculations, and each one of those 120 room calculations gets rounded up you have added 120 people to the building.
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The building/floor occupant load should never be based on a room-by-room calculation. The entire area of each different load factor should be calculated for the floor. The room occupant loads are just to make sure the requirements for that room are met.
 
dbartley said:
The building/floor occupant load should never be based on a room-by-room calculation. The entire area of each different load factor should be calculated for the floor. The room occupant loads are just to make sure the requirements for that room are met.
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yes and no

take a classroom wing in a school, each of those classrooms are individual NET calculations with each calculation getting rounded up. Large office space in simplistic terms is one large gross calculation.
 
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