Mezzanines and atriums, which one can be used best to utilize a space? While mezzanines are beneficial in that they help utilize double height spaces in increasing floor area and openness to the floor below, they come with some restrictive caveats that aim to protect life safety and wellness. Per 505.2 of the 2018 International Building Code, mezzanines can be at most 1/3 the area of the space that they are located in, with special exceptions allowed in Type I and II industrial buildings. But what do you do when you have, for example a Type III or V multifamily building, in which you would like to provide a “mezzanine” open to a posh, new co-working library space? This is where the atrium designation may come in handy. Normally you would think of atriums in grand, multi-story lobby entrances and that it would come with costly and unaesthetic restrictions regarding smoke control and/or fire barrier for the stories above. When utilizing atriums in smaller scale instance (2 stories tall) both of these restrictions may be avoided per the following exceptions:
Per 2018 IBC 404.6: A fire barrier is not required between the atrium and the adjoining spaces of up to three floors of the atrium provided that such spaces are accounted for in the design of the smoke control system.
Per 2018 IBC 404.5: In other than Group I-2 and Group I-1, Condition 2, smoke control is not required for atriums that connect only two stories.
With these exceptions, you should be able to increase the size of the “mezzanine” to greater than 1/3 the floor area while maintaining the openness visually preferred provided you still maintain the required number of exits from the upper level based on the designed occupancy. For more information about the most current IBC, visit: https://codes.iccsafe.org/content/IBC2018.
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