What distinguishes a closed mezzanine from an open mezzanine in maximum allowable area?

The distinction between a closed mezzanine and an open mezzanine primarily revolves around the amount of floorspace each can occupy within a building. A closed mezzanine typically has enclosing walls and is usually considered a full level in terms of building area calculations. This means that it has more strict limitations due to the potential impact on fire safety, egress, and overall building volume.

In building codes, a closed mezzanine generally can occupy a maximum area of 20% of the floor area of the room or space in which it is located. This percentage reflects the additional safety considerations required for closed spaces, as they can be designed for more extensive use and occupancy.

In contrast, an open mezzanine has less enclosing structure (often no walls), allowing for more maximum allowable area, which can be up to 50%. This facilitates greater flexibility in usage without compromising safety, as the open design can minimize risks associated with occupancy limits and fire egress.

Thus, the distinction is rooted in the intended use and safety implications of the different mezzanine types, with closed mezzanines being more restricted in their area allowance compared to open mezzanines.