Mezzanine Area Limitation

Mezzanines are common features that can be incorporated into building design to provide additional floor area and open space at an intermediate elevation between two stories. There are a number of provisions that outline criteria to regulate and restrict how mezzanines are constructed. These provisions limit the overall hazard of mezzanines, as well as impact the means of egress, fire protection system coverage, accessibility, structural nature, openness, and the allowable area of the mezzanine.

The size of a mezzanine will dictate if an additional space is classified as a “mezzanine” or as a “story” from a code perspective. The detailing of the area evaluation required for mezzanines can raise frequent questions, with several common ones addressed below.

The first step in determining the classification of a mezzanine is to evaluate the area of the space being considered. This process consists of finding the ratio of the area of the mezzanine in relation to the area of the room or space in which the mezzanine is located. In determining these two areas, the IBC provides the following guidelines:

  • The area of the mezzanine includes all area at the respective elevation. Enclosed rooms, means of egress, and other building features at the mezzanine level are to be included in determining the total mezzanine area.
  • The area of the room or space in which the mezzanine is located does not include any enclosed spaces at the floor in which the mezzanine is located.
  • The area of the mezzanine is not permitted to be included in the area of the room or space in which the mezzanine is located.

Note that spaces not otherwise included in determining the total building area (i.e. exterior courts, roof decks without horizontal projection of the roof, etc.) are not included in determining the area of either the mezzanine, or the floor or space in which the mezzanine is located.

Once the areas outlined above are determined, the aggregate area of a mezzanine or mezzanines within a room or space is not permitted to be greater than one of the following (IBC §505.2.1):

  • One-third the floor area of the room or space in which they are located;
  • One-half the floor area of the room or space in which they are located, provided the building is of Type I or II construction, equipped with a code-compliant automatic sprinkler system throughout, and provided with an approved emergency voice/ alarm communication system; or
  • Two-thirds the floor area of the room or space in which they are located, provided the building is of Type I or II construction and houses special industrial occupancies in accordance with IBC §503.1.1.

The area evaluation of mezzanines varies on a case by case basis, but the process of determining the area of the mezzanine and the area of the room or space in which the mezzanine is located remains consistent for all arrangements.