Hypothetical question: an entire floor of small assembly spaces, what occupancy?

[Tim Mailloux]

This is a hypothetical question that an architect in my office threw at me the other day and I didn’t know how to answer. This hypothetical project would be located in CT, 2015 IBC with state amendments.


The 2015 IBC section 303.1.2 states that small assembly type spaces (say conference rooms) with less than 50 occupants or smaller than 750SF can be classified as group B or the same as the primary occupancy which those spaces serve. Say you have a 2 story 20,000 SF office building, the entire 10,000 SF 2nd floor is clearly a B occupancy containing nothing but workstations and offices. But the entire 10,000 SF first floor consists of small 749 SF conference rooms and some circulation. By a strict reading of 2015 IBC section 303.1.2 all of those small 749 SF conference rooms can be classified as a B occupancy and the entire floor is also a B occupancy. But that just doesn’t feel right to me and I feel like that floor should be an A3 occupancy.

 

[RLGA]

Group B

 

[cda]

This is a hypothetical question that an architect in my office threw at me the other day and I didn’t know how to answer. This hypothetical project would be located in CT, 2015 IBC with state amendments.


The 2015 IBC section 303.1.2 states that small assembly type spaces (say conference rooms) with less than 50 occupants or smaller than 750SF can be classified as group B or the same as the primary occupancy which those spaces serve. Say you have a 2 story 20,000 SF office building, the entire 10,000 SF 2nd floor is clearly a B occupancy containing nothing but workstations and offices. But the entire 10,000 SF first floor consists of small 749 SF conference rooms and some circulation. By a strict reading of 2015 IBC section 303.1.2 all of those small 749 SF conference rooms can be classified as a B occupancy and the entire floor is also a B occupancy. But that just doesn’t feel right to me and I feel like that floor should be an A3 occupancy.

Agree B

303 does not say cumulative

 

[JBI]

I must agree also... B Occupancy spaces per 303.1.2(2).

As a practical matter, it will not likely 'act' like an A Occupancy during an emergency.

 

[Builder Bob]

Keep in mind, that egress still has to be designed for the intended purpose of the room not the occupancy classification of the building. In other words, you may be hard pressed to sell that concept to be @ 100 gross if every room has table and chairs and looks like a conference room which is at 15 net.

 

[Sifu]

What Bob said. Very often I have submissions that propose a conference room as a B under 303.1.2, which I agree with, but then they go on to calculate the space at 100 gross. My understanding is that the classification in instances like this is important for separation, but has nothing to do with occupant load, which is based on use. If we didn't have that code section, you could end up with fire barriers between conference rooms and office spaces (if using a IBC 508.4-separated strategy), within a suite. The OP situation could be a B occupancy, but with an occupant load that would likely overwhelm the MOE design, probably hitting the 3 exit mark. I am guessing the proposed question was along these lines.

 

[Builder Bob]

1001.1 General ---------------

 

[Tim Mailloux]

Keep in mind, that egress still has to be designed for the intended purpose of the room not the occupancy classification of the building. In other words, you may be hard pressed to sell that concept to be @ 100 gross if every room has table and chairs and looks like a conference room which is at 15 net.

I completely agree that all these conference rooms would have an 1/15SF occupant load and the floor would have a very high occupant load and also require a lot of plumbing fixture. The hypothetical question was purely about occupancy. Take the 2 story building in my hypothetical question and change it to a 2B, 4 story building with the ground floor contain nothing but small 749sf conference rooms and 3 stories above contain B office space. If the ground floor was an A3, than that building could only be 3 stories high.

 

[Tim Mailloux]

I must agree also... B Occupancy spaces per 303.1.2(2).

As a practical matter, it will not likely 'act' like an A Occupancy during an emergency.

Yet if we change all those 749SF conference rooms to 800sf conference rooms (or even 751sf) they become an A3 occupancy. The floor occupant load would probably stay roughly the same and the space would function exactly the same as with the smaller 749sf conference rooms, but it would not be an assembly occupancy.

 

[RLGA]

...Take the 2 story building in my hypothetical question and change it to a 2B, 4 story building with the ground floor contain nothing but small 749sf conference rooms and 3 stories above contain B office space. If the ground floor was an A3, than that building could only be 3 stories high.

Not if the separated occupancies method was used and the horizontal separation between the 1st and 2nd stories was a 1-hour horizontal assembly supported by 1-hour construction.

 

[Sifu]

I didn't want to open the effect on the height and area can of worms............but yes it can have that effect. Sounds like I mis-read the intent of the question, you seem to have it under control.

 

[Yikes]

I've done many "multipurpose" buildings like this, some with moveable walls between the spaces.
We would post 2 occupant loads for every space. One when closed (with classroom exit loads), another when opened where it forms an A occupancy. we calc'd exiting via both methods, and structural for the highest load.

But if, per you example, the walls were all fixed, then yes it's all B occupancy.