# Reason for 2015 IBC 505.2.1 Mezzanine Area rule?



## Martin Brice (Feb 22, 2020)

Hi, I was hoping somebody could enlighten me about the reason why the IBC (2015) 505.2.1 *forces a designer to enlarge the building* until the unenclosed areas of the room enclosing the mezzanine amount to three times the mezzanine area:

505.1 General. Mezzanines shall comply with Section 505.2. ...

505.2 Mezzanines. A mezzanine or mezzanines in compliance with Section 505.2 shall be considered a portion of the story below.  Such mezzanines shall not contribute to either the building area or number of stories as regulated by Section 503.1.  The area of the mezzanine shall be including in determining the fire area.  The clear height above and below the mezzanine floor construction shall be not less than 7 feet.

505.2.1 Area limitation.  The aggregate area of a mezzanine or mezzanines within a room shall be not greater than one-third of the floor area of that room or space in which they are located.  The enclosed portion of a room shall not be included in a determination of the floor area of the room in which the mezzanine is located...

505.2.3 Openness.  A mezzanine shall be open and unobstructed to the room in which such mezzanine is located except for walls not more than 42 inches in height, columns and posts.

Exceptions:

3. Mezzanines or portions thereof are not required to be open to the room in which the mezzanines are located, provided that the aggregate floor area of the enclosed space is not greater than 10 percent of the mezzanine area.​
So: by 505.1, all mezzanines must be "in compliance with Section 505.2".  Section 505.2.1 seems to imply that in order to have a 1000sqft mezzanine, you need to build at least a 3000sqft building, and probably much larger if any part of the ground floor (e.g. the area under the mezzanine) is enclosed.  It also seems to imply you can't have enclosed rooms taking up more than 10% of the mezzanine.

*Is this for structural/seismic reasons?  If so why is there no waiver for stamped engineered designs?  Is there some other safety justification?*

The only thing I can think of is that the maximum mezzanine area rule is to prevent developers from exploiting 505.2 wherein the mezzanine doesn't count as a story and doesn't contribute to the area (except for fire area) of the story below.  But then why forbid a large mezzanine even in situations where these area waivers aren't needed for compliance with any other aspect of the code?  In other words: if a design violates 505.2.1 but otherwise is completely 100% code-compliant when either (a) treating the mezzanine as a separate story or (b) including the mezzanine floor area in the area of the story below -- *in that case, why not allow the building to be built?*  Likewise for 505.2.3; I can see why the code doesn't want developers using mezzanine rooms to get "free floor area", but why not allow rooms on the mezzanine for buildings that aren't pushing any of the area limits?

The only way this makes sense is if a developer has the option to declare that they want an obviously-mezzanine structure to be treated as a story.  The IBC definition of story doesn't forbid this, but it sounds so counterintuitive I can't believe it's actually intentional.  *Is it the code's intent that developers get to choose if a mezzanine is treated as a mezzanine or a story?*  Is there something written somewhere to validate this?

Thanks,


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## cda (Feb 22, 2020)

Welcome


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## cda (Feb 22, 2020)

You know it is Saturday

Give it a few days for great answers


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## cda (Feb 22, 2020)

Adds area without adding a story and requirements of one???


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## RLGA (Feb 23, 2020)

If an elevated floor area is considered a story--and complies with all the requirements for a story--then it is not a mezzanine and is not limited to the area restrictions for mezzanines or any other requirement for mezzanines.


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## Mark K (Feb 23, 2020)

This requirement was not  driven  by seismic considerations.


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## TheCommish (Feb 24, 2020)

My be you should look at the mezzine as a gift, design the building first, the you are give an option to have a small mezzine area  in it. The next option is to have a 2nd story and work the design that way


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## Paul Sweet (Feb 24, 2020)

I think the 1/3 of the area open to the mezzaine restriction is so a fire on the mezzanine would be readily noticeable from the floor below, and vice versa.  At one time it was 1/3 of the story.


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## Martin Brice (Feb 25, 2020)

RLGA said:


> If an elevated floor area is considered a story--and complies with all the requirements for a story--then it is not a mezzanine and is not limited to the area restrictions for mezzanines or any other requirement for mezzanines.



Thanks RLGA, your explanation is the only way this makes sense.  Unfortunately the code doesn't say this.  All it says is that a Mezzanine is "an intermediate level or levels between the floor and ceiling of any story" where a story is "the portion of a building included between the upper surface of a floor and the upper surface of the floor or roof next above".

Obviously I want my horizontal surface to be a "floor", the space below it to be the "first story" and the space above it to be the "second story".  What I'm afraid of is the code official who says "it looks like a mezzanine, walks like a mezzanine, and quacks like a mezzanine, so it's a mezzanine, and it's 40% of the unenclosed area, so NO PERMITS FOR YOU!"

Is there some precedent or official clarification I can point them to?

It doesn't help that this second story (which is smaller than the story below it) is labeled "mezzanine" on the engineer-stamped drawings.  The building in question is a pre-engineered structural steel "red iron" building.

I get the impression that this whole "mezzanine" business is meant to deal with people who add intermediate levels to buildings that already exist.  I'm definitely not interested in doing that -- if it isn't included in the original engineering I don't want to mess with it.  Unfortunately the companies who sell these buildings (and guarantee IBC 2015 for my jurisdiction's wind+seismic) insist on calling the second floor a "mezzanine" even when it's an integral part of the building, made of the same material as the rest of the building, and constructed along with the rest of the building.


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## Martin Brice (Feb 25, 2020)

TheCommish said:


> The next option is to have a 2nd story and work the design that way



That's exactly what I want.  But if the code official decides to stick to the "letter of the code" they're likely to call it a mezzanine.



Paul Sweet said:


> I think the 1/3 of the area open to the mezzaine restriction is so a fire on the mezzanine would be readily noticeable from the floor below, and vice versa.  At one time it was 1/3 of the story.



Interesting.  But why does this requirement apply to a mezzanine but not apply to a second story?


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## Martin Brice (Feb 25, 2020)

Nevermind!  I solved it.  Leaving this message here for posterity, in case anybody else comes across this.

The IBC2015 and IRC2015 definitions of "mezzanine" are slightly different!  Both begin with the text "an intermediate level or levels between the floor and ceiling of any story".

The IBC2015 definition continues "... and in accordance with Section 505."  Section 505 includes the area restrictions.  So if a floor does not meet the 33% area requirement it isn't in accordance with Section 505 and therefore isn't a mezzanine.  The only other thing it could conceivably be is a story, which makes sense.

I think the IRC definition is really confusing.  The IBC definition should be used in the IRC as well.

My project is being permitted under the IRC (residential accessory building) using engineer-stamped IBC 2015 drawings.  Fortunately R301.1.3 allows IRC projects to use IBC-engineered designs: "engineered design in accordance with the International Building Code is permitted for buildings and structures, and parts thereof, included in the scope of this code".

Thanks again everybody.  Hopefully the next person to run into this issue won't have to spend as much time researching it as I did.


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## RLGA (Feb 25, 2020)

The definition states that a mezzanine is an "intermediate level or levels _between _the floor and ceiling of any story..."

If the level is at the floor level of the second story, then it is _not between_ the floor and ceiling of the first story.


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## ADAguy (Feb 27, 2020)

Also consider that if it were not open to the floor below it would then be a an interveening floor, no?


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## Rick18071 (Feb 28, 2020)

This was another mezzanine problem that was solved by adding an opening to a second room from the mezzanine which made it less than 1/3 of both rooms.

https://www.thebuildingcodeforum.co...smaller-room-in-a-small-building.21540/page-2


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