Fire Assemblies Defined
Robert Grupe / May 2018
Q: How are “fire wall,” “fire barrier” and “fire partition” defined??
A: AAccording to the International Building Code, there are subtle but significant differences in those terms. Any discussion on these assemblies must start with the actual definitions as found in chapter seven:
“Fire Barrier: A fire resistance rated vertical or horizontal assembly of materials complying with Section 706 designed to restrict the spread of fire in which openings are protected.
“Fire Partition: A vertical assembly of materials complying with Section 708, designed to restrict the spread of fire in which openings are protected.
“Fire Wall: A fire-resistance rated, smoke tight wall having protected openings, which restricts the spread of and extends continuously from the foundation to or through the roof, with sufficient structural stability under fire conditions to allow collapse of construction on either side without collapse of the wall.”
All three assemblies start with the requirement of a wall, or a horizontal assembly in the case of the fire barrier, that has been tested in accordance with ASTM E-119, Standard Test Methods for Fire Tests of Building Construction and Materials, and achieved a required hourly rating.
All three assemblies must have “protected openings.” This means all openings in the fire-resistive wall must be designed to restrict the possibility of the fire breaching the wall. Examples of openings include doors and penetrating items such as those common with mechanical, electrical and plumbing services.
These openings in all three cases must have been evaluated for fire performance based on the appropriate test standard. Fire barriers are more restrictive than fire partitions because the size of the protective opening is limited. Openings in a fire barrier are limited to being no more than 25 percent of the length of the wall, with a maximum single opening size restricted to 120 square feet.
Continuity of the fire resistance in all three is also important. Fire barriers are to be continuous from the floor-ceiling assembly below to the underside of the floor or roof deck or slab above. That would require that the wall would extend intact through any suspended ceiling assembly and any concealed spaces. The wording for fire partitions is similar to fire barriers except there is an allowance for fire blocking above the ceiling plane. This suggests that it is allowable to terminate a fire partition at the ceiling line if fire blocking is installed in the ceiling plenum; there are notable exceptions on this continuity requirement.
The fire wall is seen as the most “fire safe” of the three types of assemblies. Part of this reasoning is based on the continuity requirement of the wall. The wall must extend from the foundation to or through the roof. Also, there is the structural requirement that states that if the structure on one side of the wall collapses, the fire wall remains intact and protects the structure on the other side.
The type of wall that will be used is also mandated by the code. Fire partitions are used to separate individual dwelling or sleeping units within the same building, to separate individual tenant spaces such as in covered malls, in corridor walls and in elevator lobbies.
Fire barriers are to separate individual shafts and exit passageways. Other applications include horizontal exits or to separate a single occupancy into different “fire areas.”
The fire wall is seen as dividing a large building into two smaller buildings, thus the requirements for the continuity of the fire resistance and the structural independence on either side of the wall. Also, this requirement is used when new construction is tied into an existing structure. It is sometimes used as a “party wall” to separate a building that crosses a lot line. In this case, the one building is divided into two buildings with a fire wall at the lot line.
A fire resistance rated wall selected from GA-600, Fire Resistance Design Manual, will most likely work in all three assemblies. Penetrations are allowed in all three cases, but they must be protected. This means that the same through penetration firestop system will most likely work in all three cases. The exception would be the party wall where no penetrations are allowed. Construction joints, such as head of wall designs or control joints, can be similar.
Continuity would be an area where the contractor must understand the nuances, for the fire wall is not only the vertical continuity; there are requirements for horizontal projections. Another installation challenge is where the fire wall separates a building of two different heights. An example would be a fire wall that separates a two-story structure from one that is three stories. There are certain requirements as to how high the wall must extend above the lower building roof line.
An issue of concern in continuity is prioritization of walls. An example of this is where a two-hour fire-resistive wall intersects a one-hour or non-rated wall. The two-hour wall, because of continuity requirements, must be continuous through that intersection. To do this properly the contractor must pay attention to how this impacts the framing, and how it changes the sequence of installing the gypsum panels.
The differences and local interpretation of fire barriers, fire partitions and fire walls will be exposed by the authority having jurisdiction, and the knowledgeable contractor will foresee issues prior to inspection.
Robert Grupe is AWCI’s director of technical services. Send your questions to firstname.lastname@example.org, or call him directly at (703) 538.1611.