Room occupant load calculations: round up or down?

[Tim Mailloux]

The plain text reading of 1004.5 states ‘the number of occupants shall be computed at the rate of one occupant per unit of area as prescribed in Table 1004.5’. There is nothing in that language about partial occupants, partial units of area or rounding up. Until you reach the next whole unit of area per table 1004.5 for the correct function of space, you don’t add an occupant.

 

[Yankee Chronicler]

There is also nothing in there about rounding down. All I can do is pass along how it has been done for the past 50 years.

 

[arwat23]

I would typically group all those offices, exam rooms and supporting corridors, toilets rooms, under one large 1 per 150 gross business area calculation. any conference rooms & waiting area would have individual net calculations using the appropriate assembly occupant load factor. There would only be a hand full of calculations getting rounded up and this would not have much of an impact on Occupant loads.

Our firm use to do that, but in the past few years more and more jurisitication have been demanding that we calculate each room individually, even if it's a gross load factor. Their reasoning is that, other than code allowing for calculating each room individually (code says "spaces" which can be defined in our code as an individual room), realistically, every room could have at least one person in them all at the same time.

Let's say you have ten 100 s.f. offices. 1,000 s.f. total. That's 6 or 7 occupants depending on how you round. So that means three offices don't have anyone in them. Logically, that doesn't make much sense, depending on the project at least.

 

[mtlogcabin]

[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.

All I can do is pass along how it has been done for the past 50 years.

Up or down right or wrong consistency is always a good practice to follow.

 

[SCBO1]

Our firm use to do that, but in the past few years more and more jurisitication have been demanding that we calculate each room individually, even if it's a gross load factor

That change or request could be like when a restaurant has several walled off rooms the code requires the OL posted in each assembly room. A steak house that I have gone to, has four separate dining rooms with each room posted. So when calculating each room you could easily come up with fractions in each room resulting in rounding up or down. Four separate rooms with OL fractions rounded up would add 4 additional patrons to the OL or if rounding down reduce the OL.

 

[Paul Sweet]

Having to show the number of occupants for each space with fewer than 50 occupants doesn't make sense. An office might calculate to a fraction of an occupant, but the 32" clear opening door to that office is adequate for 160 occupants in an unsprinklered building, and 213 in a sprinklered building.

 

[steveray]

Having to show the number of occupants for each space with fewer than 50 occupants doesn't make sense.

Until they are using the same door or corridor and it affects door swing or egress width.....

 

[arwat23]

That change or request could be like when a restaurant has several walled off rooms the code requires the OL posted in each assembly room. A steak house that I have gone to, has four separate dining rooms with each room posted. So when calculating each room you could easily come up with fractions in each room resulting in rounding up or down. Four separate rooms with OL fractions rounded up would add 4 additional patrons to the OL or if rounding down reduce the OL.

Yeah, it caused quite a headache on a recent project. The jurisitication required us to round up every single room regardless of size or load factor type (all were gross load factors, most sharing walls). I did some quick math at the time and it "added" roughly 40 occupants to the building (compared to if we didn't calculate each room individually or didn't need to round up). Almost pushed us over the OL where plumbing (WCs mainly) would've become a bit of pain to design around.

 

[JPohling]

We handle this a bit different. We show every room and space on the egress plan calculated and rounded up. This allows the exiting to be checked for each room specifically. We never total these rounded up occupant load rooms and spaces as you have noted that would lead to a massive increase. We simply add all of the same occupancies together as a lump sum square footage and then round that up. all office sf totaled /150. all conference room sf totaled/15 all storage sf/300 = suite occupant load

 

[Inspector Gadget]

I was taught to round up.

Having to show the number of occupants for each space with fewer than 50 occupants doesn't make sense. An office might calculate to a fraction of an occupant, but the 32" clear opening door to that office is adequate for 160 occupants in an unsprinklered building, and 213 in a sprinklered building.

Up here, occupant load also drives washroom counts. I assume the same for south of the 49th?

 

[walker.t]

In those cases do you round your math up or down?

I was taught to use the more conservative method and round up. Tonight I was surprised to see that the 2018 IBC Illustrated Handbook has a sample calculation where they rounded down:

From 2018 IBC Illustrated Handbook Application Example 1004-2 [partial quote]
[This example considers what to do in a multi-purpose room which could be used as a conference room with table and chairs or with only chairs.]

(1) Conference/seminar use with tables and chairs
1 person per 15 sq ft = 106.67 = 106 occupants

(2) Conference/seminar use with chairs only (auditorium-style seating)
1 person per 7 sq ft for seating = 228.57 = 228
Therefore for egress purposes, a design occupant load of 228 shall be used.

 

[Tim Mailloux]

I was taught to use the more conservative method and round up. Tonight I was surprised to see that the 2018 IBC Illustrated Handbook has a sample calculation where they rounded down:

Using section 303.1.2 Small Assembly spaces for comparison’s sake, the section states that small assembly spaces with less than 50 people or under 750sf shall be classified as group B. Most small assembly spaces get occupant loads calculated at a rate of 1 person per 15sf sf of area. Mathematically speaking this perfectly establishes the 50 people to 750 sf relation ship defined in 303.1.2 as 750 / 15 = 50. Now if rounding up occupant load calculations is the rule of thumb, any small assembly space greater than 735 sf would have an occupant load of 50 due to rounding and would be required to be an A occupancy.

 

[Tim Mailloux]

1004.5 states ‘the number of occupants shall be computed at the rate of one occupant per unit of area as prescribed in Table 1004.5’.

Using the text of the code section as the basis of a mathematical word problem its apparent to me that (1) whole occupant gets assigned to (1) whole unit of area (per table 1004.5), and any remainders in the calculation have not reached the 'unit of area' threshold to require an occupant. This logic would align with the The 2021 IBC Code Illustrated Handbook example of rounding down. This seems to be a case of everyone defaulting to what they have always done.......becuase?..........instead of reading what the code actual says.

 

[princeofpen]

For your 1000 sq ft classrooms just remove casework and you're good. T1004.5 goes by net not gross

 

[Paul Sweet]

Until they are using the same door or corridor and it affects door swing or egress width.....

Use the total area of the offices or other spaces opening into a corridor or having a common exit and divide by the area per occupant.

 

[steveray]

For your 1000 sq ft classrooms just remove casework and you're good. T1004.5 goes by net not gross

Tim and I have spoken about that...

 

[Tim Mailloux]

Use the total area of the offices or other spaces opening into a corridor or having a common exit and divide by the area per occupant.

we typically have under 20sf of casework in a classroom, i thin the average is about 16sf.

 

[Yikes]

As an architect:
1. I show the fractions for each room.
2. I round up for determining each room's own exit components.
3. But where occupants converge, such as in hallways, etc., I first all the (non-rounded) fractional numbers from each room that feed into it, then I do one final rounding. This is helpful when I'm on the edge of triggering other issues, including plumbing fixture counts etc.

Example:

An 1400 SF office use with a business Occupant Load Factor of 150 has a gross occupancy of 9.3 occupants. Round that up to 10. The California plumbing code 422.10 exc. #2 will allow a single unisex restroom to serve 10 occupants.

It also has 16 rooms that are 60 SF each. 60 SF/ 150 SF OLF = 0.4 occupants per room. So each room's door needs to be rounded up for one occupant.
But 16 offices doesn't mean a cumulative occupant load of 16 people from those offices.
Instead, their cumulative occupant load that converges into the common areas could be 16 rooms x 0.4 per room = 6.4 occupants. The final rounding makes it 7 occupants from those rooms.

 

[steveray]

As an architect:
1. I show the fractions for each room.
2. I round up for determining each room's own exit components.
3. But where occupants converge, such as in hallways, etc., I first all the (non-rounded) fractional numbers from each room that feed into it, then I do one final rounding. This is helpful when I'm on the edge of triggering other issues, including plumbing fixture counts etc.

Example:

An 1400 SF office use with a business Occupant Load Factor of 150 has a gross occupancy of 9.3 occupants. Round that up to 10. The California plumbing code 422.10 exc. #2 will allow a single unisex restroom to serve 10 occupants.

It also has 16 rooms that are 60 SF each. 60 SF/ 150 SF OLF = 0.4 occupants per room. So each room's door needs to be rounded up for one occupant.
But 16 offices doesn't mean a cumulative occupant load of 16 people from those offices.
Instead, their cumulative occupant load that converges into the common areas could be 16 rooms x 0.4 per room = 6.4 occupants. The final rounding makes it 7 occupants from those rooms.

And there you go....a reasonable approach.....

 

[Penguin87]

Table 1004.5 says "maximum floor area allowances per occupant"

It seems like many of you are viewing this from the perspective of "occupants per area" vs what the code is stating, which is "area per occupant." There is a huge difference - in that you cannot have fractional people:
Occupant != partial occupant. You logically cannot have a part of a person as an occupant.

Therefore, the table denotes how much square footage per function of space you are allowed per person (see note a.: "floor area in square feet per occupant")

This requires rounding up in all circumstances when calculating occupancy for a space, which is defined as basically any room or enclosed space as part of a building under chapter 2.

Code commentary backs this up as well.

 

[Penguin87]

As an architect:
1. I show the fractions for each room.
2. I round up for determining each room's own exit components.
3. But where occupants converge, such as in hallways, etc., I first all the (non-rounded) fractional numbers from each room that feed into it, then I do one final rounding. This is helpful when I'm on the edge of triggering other issues, including plumbing fixture counts etc.

Example:

An 1400 SF office use with a business Occupant Load Factor of 150 has a gross occupancy of 9.3 occupants. Round that up to 10. The California plumbing code 422.10 exc. #2 will allow a single unisex restroom to serve 10 occupants.

It also has 16 rooms that are 60 SF each. 60 SF/ 150 SF OLF = 0.4 occupants per room. So each room's door needs to be rounded up for one occupant.
But 16 offices doesn't mean a cumulative occupant load of 16 people from those offices.

But doesn't it? 16 offices would typically be filled with 16 actual office workers! You aren't going to have each office filled with 0.4 of a person.

Instead, their cumulative occupant load that converges into the common areas could be 16 rooms x 0.4 per room = 6.4 occupants. The final rounding makes it 7 occupants from those rooms.

Sorry, this does not work although most building officials probably won't care either way, since the width per occupant at an egress door is what, 0.2"?

In any case, the plumbing code occupancy is separate from the life safety code and egress calculations. You can often argue to provide plumbing fixtures for the actual estimated # of employees, instead of calculated egress values. For instance, a 400,000 warehouse with 20 employees as S-1 would otherwise require dozens of plumbing fixtures that will never be used. Most building officials will be receptive to this argument.

On the other hand, in a public facility or assembly space it would be a harder sell to provide fewer fixtures.

 

[Mr. Inspector]

Munchkins may be considered a fraction of an occupant.

 

[steveray]

In any case, the plumbing code occupancy is separate from the life safety code and egress calculations.

Not in ICC land...

 

[Yikes]

But doesn't it? 16 offices would typically be filled with 16 actual office workers! You aren't going to have each office filled with 0.4 of a person.

Think of it the other way: After construction is complete, 1400 SF office space that is 14'x100' with no walls could potentially get furnished by some tenant with (20) 5' desks along each long wall, total of 40 people. But the code has set the OLF at 150, and so the exiting system for the building would still be predicated on 10 people.
Conversely, the 16 rooms in my example might be for something other than offices: files, an IT system, a lounge room, a break room, a specialized computer, copier room, mail room, janitor room, video chat room, coat room, etc. that are going to be used by the same people already counted in the other rooms, so 16 rooms does not necessitate a conclusion there are 16 occupants.
That's why we simplify to 150 gross square feet.

Sorry, this does not work although most building officials probably won't care either way, since the width per occupant at an egress door is what, 0.2"?

In any case, the plumbing code occupancy is separate from the life safety code and egress calculations. You can often argue to provide plumbing fixtures for the actual estimated # of employees, instead of calculated egress values. For instance, a 400,000 warehouse with 20 employees as S-1 would otherwise require dozens of plumbing fixtures that will never be used. Most building officials will be receptive to this argument.

On the other hand, in a public facility or assembly space it would be a harder sell to provide fewer fixtures.

The plumbing code was just one example. In fact, the entire building I described here was a hypothetical example. But I have seen real-world examples involving means of egress, where rounding every individual room upward kicked the occ. load over 49, requiring a second exit where none could be provided due to site constraints. Or going higher than 30 meant a door had to swing outward, into another hallway or space that was not big enough for accessibility clearances, etc.