Fire Walls

A fire wall is a wall that forms a required separation to restrict the spread of fire through a building and extends continuously from the foundation to or through the roof. A fire wall is used to divide a single building into smaller units, each of which may be considered as a separate building when calculating allowable heights and areas under the building code. A fire wall must either meet a noncombustible roof structure at the top or extend through and above the roof by a specified minimum distance, 30 inches (762 mm) in the case of the International Building Code (IBC). In this code, a fire wall must also extend horizontally at least 18 inches (457 mm) beyond the exterior walls of the building unless these exterior walls meet certain fire resistance and combustibility requirements. Except in buildings of Type V construction, a fire wall must be framed with noncombustible materials such as steel studs. A fire wall must also have sufficient structural stability during a building fire to allow collapse of the construction on either side without itself collapsing.

Openings in fire walls are restricted in size and aggregate area and must be closed with fire doors or fire-rated glass. The required fire resistance ratings for fire walls under the International Building Code are defined in Figure 1.7.

Shaft Walls

A shaft wall is used to enclose a multistory opening through a building, such as an elevator shaft or a shaft for ductwork, conduits, or pipes. In the International Building Code, a shaft wall connecting four or more floors must have a fire resistance rating of 2 hours or, if connecting fewer floors, a rating of 1 hour. Walls for elevator shafts must be able to withstand the air pressure and suction loads placed on them by the movements of the elevator cars within the shaft, and should be designed to prevent the noise of the elevator machinery from reaching other areas of the building.

Fire Barriers and Fire Partitions

Fire-rated walls are also used to restrict the spread of fire and smoke within a single building. Depending on the type of separation, the International Building Code requires such walls to be constructed as either fire barriers or fire partitions. Unlike fire walls, these wall types do not necessarily extend from foundation to roof. A fire barrier must extend vertically from the top of one floor slab to the underside of the next. Requirements for a fire partition are even less stringent. In some cases, a fire partition may terminate at the underside of a suspended ceiling. Fire barriers are used to protect exit stair enclosures, to separate different occupancies, and to limit the extent of fire areas (areas bounded by fire-resistant construction, the size and location within the building of which are related to automatic sprinkler requirements). Fire partitions are used to enclose corridors and to separate tenant spaces in mall buildings or dwelling units in hotels, dormitories, and other multidwelling unit buildings.

Openings in fire barriers and fire partitions are restricted in size and must be closed with fire doors or fire-rated glass. Required fire resistance ratings for the various types of fire barriers and partitions according to the International Building Code are listed in Figures 22.6 and 22.7.

The structural elements that support fire barriers and fire partitions must have a fire resistance rating at least as great as that of the wall being supported. For example, in a building of Type IIB construction, the structure is normally permitted to be unprotected. However, columns, bearing walls, and portions of the floor structure that support a 1-hour rated corridor wall must themselves also be protected with at least a 1-hour fire resistance rating.

Smoke Barriers and Smoke Partitions

In certain institutional occupancies such as hospitals and prisons, where occupants are unable to leave the building in case of fire, special partitions called smoke barriers are required. This type of wall divides floors of buildings in such a way that occupants may take refuge in case of fire by moving to the side of the smoke barrier that is away from the fire without having to exit the building. A smoke barrier is a 1-hour rated partition that is continuous from one side of the building to the other and from the top of a floor slab to the bottom of the slab on the floor above. It must be sealed at all edges. Penetrations for air ducts must be protected with dampers that close automatically if smoke is detected in the air. Other penetrations, such as those for pipes and conduits, must be sealed airtight. Doors through smoke barriers are necessary to allow movement of people in case of fire. They must be close fitting, without grilles or louvers, and must close automatically.

A smoke partition is a wall constructed—like a smoke barrier—to resist the passage of smoke, but without any fire resistance rating. For example, when walls for corridors and elevator lobbies need not be fire-rated, they are constructed as smoke partitions.

Other Nonbearing Partitions

Many of the partitions in a building neither bear a structural load nor are required as fire separation walls. These may be made of any material that meets the combustibility provisions of the building code for the selected type of construction, as explained in the next section.