The 3 categories of fire-resistant assemblies, and what you should know about each.

If you work in architecture, engineering or construction, you’ve likely heard or used the term “fire wall” to denote a fire resistance-rated wall assembly. You, or a project team member, may also have been asked to use a more specific term than ‘fire wall’. Here’s why.

The International Building Code (IBC) breaks out fire resistance-rated wall assemblies into three categories – 1) fire partitions, 2) fire barriers and 3) fire walls. Eirene Knott, our Director of Code Services and a Certified Fire Marshal as well as a Master Code Professional, regularly works with our project studios to implement all three of these assemblies, and helped us further define the differences between each. Here is a quick guide to the three categories of fire resistance-rated wall assemblies, and when to use and denote each.

Fire Partitions

Fire partitions are the least restrictive of the three assemblies, and have a minimum fire-resistance rating of 1 hour. Partitions are most-commonly used between mall tenants, or separate dwelling or sleeping units, as well as in elevator lobbies or corridors.

What else you should know: 

+ The rating for fire partitions can be reduced when used to separate dwelling or sleeping units in Type IIB, IIIB, or VB construction if an automatic sprinkler system complying with NFPA 13 is provided throughout the building.
+ The reduction can also apply when code allows for a corridor wall to be a 30-minute assembly.
+ Fire partitions must extend from the top of the floor below, to the underside of the floor or roof sheathing …
+ OR, to the underside of the fire resistance-rated floor/ceiling, or roof/ceiling assembly above.
+ Openings, penetrations, joints and duct/air openings must be protected.

 

 

 

Fire Barriers

The IBC defines fire barriers as a “fire resistance-rated wall assembly of materials designed to restrict the spread of fire in which continuity is maintained.” Fire barriers include walls and horizontal assemblies, and vary in their rating between 1 and 4 hours. They typically separate occupancy classifications, atriums, exit stairways, shafts and fire areas.

What else you should know:

+ Fire barriers must extend from the top of the floor/ceiling assembly below, to the underside of the floor or roof sheathing, slab or deck above.
+ Barriers must be continuous through concealed locations, like the space above a suspended ceiling.
+ Any construction supporting a barrier must be protected to the same rating as the barrier.
+ Openings, penetrations, joints and duct/air openings must be protected.

 

 

 

 

 

Fire Walls

Fire walls are the most restrictive fire resistance-rated assembly, and create separate buildings for determining allowable area. Unlike partitions or barriers, fire walls must be vertical, and have a 2-hour minimum/4-hour maximum rating.

What else you should know:

+ Fire walls must provide for structural collapse on either side of the wall, without the wall collapsing.
+ Except when in building using Type V construction, walls must be made of non-combustible materials.
+ For vertical continuity, walls should extend from the foundation, to a point at least 30 inches above the roofs on both sides of the wall.
+ A wall must also extend horizontally to avoid potential fire spread from one building to the other around the wall.
+ The IBC does have exceptions for both horizontal and vertical wall continuity – be sure to check the code and verify the required continuity of your proposed wall.
+ Openings, penetrations and joints must be protected.