A mezzanine (or in French, an entresol) is, strictly speaking, an intermediate floor in a building which is partly open to the double-height ceilinged floor below, or which does not extend over the whole floorspace of the building. However, the term is often used loosely for the floor above the ground floor, especially where a very high original ground floor has been split horizontally into two floors.
Mezzanines may serve a wide variety of functions. Industrial mezzanines, such as those used in warehouses, may be temporary or semi-permanent structures.
In French architecture entresol also means a room created by partitioning that does not go up all the way to the ceiling; these were historically common in France, for example in the apartments for the nobility at the Palace of Versailles.
A mezzanine is an intermediate floor (or floors) in a building which is open to the floor below. It is placed halfway up the wall on a floor which has a ceiling at least twice as high as a floor with minimum height. A mezzanine does not count as one of the floors in a building, and generally does not count in determining maximum floorspace. The International Building Code permits a mezzanine to have as much as one-third of the floor space of the floor below. Local building codes may vary somewhat from this standard. A space may have more than one mezzanine, as long as the sum total of floor space of all the mezzanines is not greater than one-third the floor space of the complete floor below.
Mezzanines help to make a high-ceilinged space feel more personal and less vast, and can create additional floor space. Mezzanines, however, may have lower-than-normal ceilings due to their location. The term "mezzanine" does not imply a function, as mezzanines can be used for a wide array of purposes.
In industrial settings, mezzanines may be installed (rather than built as part of the structure) in high-ceilinged spaces such as warehouses. These semi-permanent structures are usually free-standing, can be dismantled and relocated, and are sold commercially. Industrial mezzanine structures can be supported by structural steel columns and elements, or by racks or shelves. Depending on the span and the run of the mezzanine, different materials may be used for the mezzanine's deck. Some industrial mezzanines may also include enclosed, paneled office space on their upper levels.
Industrial mezzanines are typically not constructed of wood, although advancements in the engineering of composite lumber in the late 1990s and early 21st century greatly increased the viability of wood-based products as a mezzanine flooring solution. While mezzanines made out of wood are traditionally considered only as a solution for storage and not for material handling purposes, composite lumber panels are a commonly used for elevated platforms or in LEED certified warehouses due to the presence of recycled contents in the compost and a decreased dependency on the amount of structural steel required to raise the platform.
An architect is sometimes hired to help determine whether the floor of the building can support a mezzanine (and how heavy the mezzanine may be), and to design the appropriate mezzanine.