Martin Brice
GREENHORN
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:
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,
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.
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.
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,