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Net floor area, built in casework and occupant load calcs

T

Tim Mailloux

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Hartford CT
A number of people in my office are under the impression that in room or space that calls for a NET area calculation per Table 1004.1.2 such as classroom and conference rooms, you can deduct the area for built in casework from the area of the room, thus reducing that square footage subject to the occupant load calculation. This doesn’t seem right to me and I wanted the opinions of the experts on this forum.


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


Base on the definition of floor area Net, I would say the area of built in casework would need to be included in the calculations.
 
I would agree, the area of built-in casework would need to be included. But I suppose you could argue that that area is "unoccupied" if you had a sympathetic AHJ. As an architect I wouldn't be comfortable not including the area. If I had a situation close enough that it mattered I would try and make the room just a little smaller.
 
I would count it for means of egress sizing but I would not count it for posting the occupant load. Casework can be removed and you would never be aware of it.
 
Could make the argument either way...

Net area is intended to be only the occupiable area; gross is the entire area (including walls). Based upon this principle, built-in furnishings could be deducted when calculating net area.

However, if the built-ins are removed (most AHJ would not require a permit for this), the architect could be in a bind if this creates an increase in occupant load that has a significant impact (i.e. - change from 49 to 50 occ, etc.). While most occurrences would be insignificant, it could theoretically lead to an issue.
 
mtlogcabin said:
I would count it for means of egress sizing but I would not count it for posting the occupant load. Casework can be removed and you would never be aware of it.
Click to expand...
Walls can be removed and you would never be aware of it.

One cannot assume more than what is shown on the submitted documents.
 
If it is unoccupied or unoccupiable, you don't count it. Kind of like a big built in planter or fountain....I did sleep in my bookcase once, but that is a longer story....
 
This issue came up on a school project my office is designing and the project team was deducting some built in cabinets with counter tops along the exterior wall from the Net area of the classroom. This was being done to get the net area of the classroom below 1,000sf / 50 occupants and do away with the need for two exits and exit separation in these classroom. I reached out to the ICC last week for a code interpretation on this situation and I was told that it was never the ICC’s intention for built-in case work (as I described) from being deducted from the classrooms Net area. I have also reached out to the CT State Building Official for his take on the matter and I am still waiting to hear back.
 
Tim Mailloux said:
This issue came up on a school project my office is designing and the project team was deducting some built in cabinets with counter tops along the exterior wall from the Net area of the classroom. This was being done to get the net area of the classroom below 1,000sf / 50 occupants and do away with the need for two exits and exit separation in these classroom. I reached out to the ICC last week for a code interpretation on this situation and I was told that it was never the ICC’s intention for built-in case work (as I described) from being deducted from the classrooms Net area. I have also reached out to the CT State Building Official for his take on the matter and I am still waiting to hear back.
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Interesting. If the intent was not to allow built-in casework to be excluded, then the definition of net floor area should have been more precise. There is no definition for "occupied area" as used in the net floor area definition, and built-in casework does deny the use of the floor by occupants. So, as it currently stands, an interpretation by a building official could go either way.

The IBC Handbook (endorsed by ICC since it bears its logo) never mentions built-in casework, but only FF&E, as being included in determining net floor area.

Additionally, the IBC Commentary mentions neither but states that it is "typically measured between inside faces of walls within a room," which means there are situations where it is not measured to the inside faces of walls, but it never explains what those situations may be--casework would be the most common in my opinion.
 
From Building Codes Illustrated, 4th edition, based on the 2012 IBC
"It is expected that the interpretation of these terms [net and gross] will be that net refers to the actual area where occupants may stand, ..........."
I understand this is not a code book or code reference, merely an informed opinion, but it makes sense to not include an area that a human can't occupy. However, if an opinion or interpretation has been provided by ICC clarifying this issue I would have to consider revising my own opinion. Did they provide a written response? Usually they respond via email to me, however a few times I have had them call me directly to discuss the question and only after some clarification and a specific request for the results in writing does that happen. If they did give you a written opinion could you share it with me/us?
 
I thought that the main reason the code allows 50 SF per person for labs vs. 20 for classrooms is because of all the built-in tables, counters, equipment, etc.

The definition of net floor area is to contrast it with gross floor area, which includes unoccupied spaces, walls, shafts, etc.
 
Paul Sweet said:
I thought that the main reason the code allows 50 SF per person for labs vs. 20 for classrooms is because of all the built-in tables, counters, equipment, etc.

The definition of net floor area is to contrast it with gross floor area, which includes unoccupied spaces, walls, shafts, etc.
Click to expand...
Actually, 50 sf is for "Shops and other vocational room areas," which may include some labs; however, many shops and vocational areas consist of spaces with large pieces of (somewhat) moveable equipment which is to be included in the net floor area (at least per the IBC Handbook).
 
If it is possible to reference the IMC for this questionable design practice not exactly covered in the IBC, IMC has a definition: NET OCCUPIABLE FLOOR AREA. The floor area of an occupiable space defined by the inside surfaces of its walls but excluding shafts, column enclosures and other permanently enclosed, inaccessible and unoccupiable areas. Obstructions in the space such as furnishings, display or storage racks and other obstructions, whether temporary or permanent, shall not be deducted from the space area.
 
Call it a closet with a counter on top of it...Problem solved!...As far as things being changed around without permit, we already have code for that....

[A] 105.2 Work exempt from permit. Exemptions from
permit requirements of this code shall not be deemed to grant
authorization for any work to be done in any manner in violation
of the provisions of this code or any other laws or ordinances
 
Tenants in commercial buildings love this question as it directly effects rental square footage.
As usual, "it depends" on the AHJ.
 
ADAguy said:
Tenants in commercial buildings love this question as it directly effects rental square footage.
As usual, "it depends" on the AHJ.
Click to expand...
ADA guy, the amount of cabinetry within a suite will not affect the Rentable Square Footage for a space as calculated per BOMA
 
This is interesting but I would not subtract the build-in cabinets from the occupiable space. Most of the the time built-in cabinets are just screwed onto the walls like kitchen cabinets or lab tables would have just a few screws into the the floor. When this room is re-finished in a few years the first thing that goes are these built-in cabinets.
 
As to "space occupied", cabinets are typically "fixed" in place (as in siesmicly attached) unlike furniture and people.
Usually people cannot occupy the same space as cabinets, except for Murphy beds.
 
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