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Mezzanine Area Limitation (IBC 2015 505.2.1)

fungineer

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Feb 12, 2021
Messages
34
Location
Milwaukee, WI
I have a question regarding 505.2.1 (within IBC 2015).

This section states: The aggregate area of a mezzanine or mezzanines with a a room shall be not greater than one-thirds of the floor area of the room or space in which they are located. The enclosed portion of a room shall not e included in a determination of the floor area of the room in which the mezzanine is located. In the determining the allolwable mezzanine area, the area of the mezzanine shall not be included in the floor area of the room.

Specifically, I have 2 questions.
I've used images from he Canadian building code appendix (as the IBC didn't have images in the commentary) for reference.
https://ibb.co/7JZjVQf

For the first, If my overall floor area is 1000 sq ft (for example only), and my mezzanine is 100 sq ft, does the first part of this definition state that the open area of the room is 900 (because 1000-100 = 900)? If the area under the mezzanine had walls up to the mezzanine, does the 900 sq foot number change?

Second question. If In in my 1000 sq foot room containing a 100 sq ft mezzanine I want to build an enclosed office on the 1st floor, with a dust cap above, does my overall floor area shrink by the enclosed space? Does the answer matter if the walls to this enclosed space is full height or not (see second image)?
 
I should revise the first question, looking at the commentary:

1000 sq foot space.
-The area of the room is 1000 because although the fire area is 1100, you don't include the 100. You would then deduct 100 sq feet if the area under the mezzanine were enclosed, correct?
 
The way I understand it is that the the mezzanine area can't exceed 1/3 of the area of the room it opens into. You don't add or subtract the mezzanine area from the room area.

505.2.1 says "... The area of the mezzanine shall be included in determining the fire area. ..." I suspect that some people tried to push the envelope to say this also allowed you to add the mezzanine area to the room area before taking 1/3 of the total.
 
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