The Problem with Mezzanines
NFPA 101® has specific requirements for construction of intermediate levels.
NFPA Journal®, January/February 2009
The construction of mezzanines can create problems without the designer or user realizing it. The 2009 edition of NFPA 101®, Life Safety Code®, defines a mezzanine as “an intermediate level between the floor and the ceiling of any room or space.” The size of a mezzanine is quite specific. Section 8.6.9 includes requirements for mezzanines and limits their size to one-third of the open area in which they’re located.
This is an important criterion. If the area of the mezzanine is greater than one-third of the open area, it is not a mezzanine but a floor. When the space becomes a floor, several additional code requirements may be triggered. Floors generally require two separate and remote exits, and the Life Safety Code has specific requirements for separating floors and limiting openings between them, as required in Section 8.6, Vertical Openings. In addition, adding another story to the building can change the type of construction required as noted in Section 1.6, Minimum Construction Requirements, of each occupancy chapter.
The pitfalls facing designers may seem tricky. A designer who merely expands the area of an existing mezzanine may not realize he’s crossed a line in terms of space and is now violating a code requirement.
A more common problem occurs when the designer encloses the area beneath the mezzanine with a solid wall. This reduces the area onto which the mezzanine opens, and the area of the mezzanine may now exceed the allowable one-third of space onto which it opens. Fixing these pitfalls can be simple. For example, using chain-link fencing to enclose the space under the mezzanine solves the need for division without violating the open space requirement.
Another problem occurs when designers enclose the mezzanine. This may be done to minimize noise and dust or for security purposes, but it ignores Section 18.104.22.168, which requires two separate means of egress, one of which must be an exit directly from the mezzanine level if the occupant loading of the enclosed space exceeds 10 people.
The construction of a mezzanine can significantly increase the common path of travel distance in the room. Without the mezzanine, the common path of travel is measured from the most remote occupiable point to a point of choice to reach two separate and remote exits. Often, that point is the door to the room, as when the occupant steps into the corridor and has the choice of going right or left to reach separate exits. When a mezzanine is added, however, the most remote point in the room often becomes the back corner of the mezzanine. The distance across the mezzanine, down the mezzanine stairs, and across the room to the corridor door can exceed the permitted common path of travel.
Sprinkler protection below a mezzanine can also be an issue. Designers often use open-grated flooring because they think sprinkler protection below the mezzanine is not needed, since the sprinkler water can penetrate the open grating. The 2007 edition of NFPA 13, Installation of Sprinkler Systems, states in Section 22.214.171.124.1 that “sprinklers shall be installed under fixed obstructions over 4 feet (1.2 meters) wide such as ducts, decks, open-grate flooring, cutting tables, and overhead doors.” Any obstruction wider than 4 feet (1.2 meters) requires sprinklers under the obstruction, including open-grated mezzanines. This requirement has been in NFPA 13 for some time.
The construction of mezzanines can often provide additional needed space, but remember: the details of the mezzanine construction must be observed to ensure code compliance.
Chip Carson, P.E., is president of Carson Associates, Inc., a fire engineering and code consultancy. He is a former member of NFPA’s Board of Directors.