9/16/2020 FIRE SEPARATION REQUIREMENTS IN THE IBC - John P. Stoppi Jr., PE, FPE.
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FIRE SEPARATION REQUIREMENTS IN THE IBC
APRIL 21, 2019
One of the more confusing aspects of the IBC (The International Code Council, 2014) and
one of the most common questions poised to a building engineer or architect is “When
are f ire separations required?” There is no simple answer to this question, because
sometimes f ire separation is a design alternative to sprinklering the entire building or
portions thereof. See my earlier article “WHEN ARE FIRE SPRINKLERS REQUIRED FOR
NEW CONSTRUCTION?” for when sprinklers are required in buildings. This article uses the
2015 IBC as its basis, as that is the most common model code year for which commercial
buildings are currently being built.
Four concepts must be introduced in order to understand f ire separations. These
concepts are: Privacy - Terms
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1. Building Area
2. Construction Type
3. Fire Area
4. Mixed building use and occupancy
5. Incidental use separation
The building area is the area between exterior walls, excluding courts and vent shafts.
When building area is mentioned in the IBC, it normally refers to the area of the largest
story, which is typically the f irst floor. Per Section B505.2, the area of mezzanines are not
included in determination of building area, but are included in the determination of f ire
area. Equipment platforms, per Section B505.3 are not used in determining the building
area or the f ire area.
The f ire area is the combined area of the floor in between f ire walls, f ire barriers, exterior
walls or horizontal (f ire barrier) assemblies within a building. Note that, in this def inition,
multiple stories can be included in the calculation for f ire area if each floor/ceiling
assemblies separating each story are not rated horizontal assemblies (f ire barriers). Also
note that f ire partitions do not count in bounding f ire areas. The f igures below, excerpted
f rom Figures 202.6(1) and 202.8(3) of the 2012 IBC Commentary (The International Code
Council, 2011), show f ire areas bounded by walls and ones bounded and unbounded by
horizontal assemblies (rated and non rated).
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Fire area appears in the building code mostly in Chapter 9 where it is used as a threshold
for requiring either f ire separation or f ire sprinkler systems. For example, Section 903.2.9,
states that one threshold of sprinklering the entire building is when such a building
contains a Group S-1 f ire area of greater than 12,000 square feet. In this case, the entire
building would have to be sprinklered, or f ire barriers would have to be constructed to
limit each Group S-1 f ire area to 12,000 square feet or less. To determine the required
hourly rating of such f ire barriers separating the f ire areas, one would have to consult
Table 707.3.10. For separating Group S-1 f ire areas f rom Group S-1 f ire areas, a 3 hour rated
f ire barrier is required.
A building’s Use and Occupancy Classif ication is the category in the IBC that is assigned to
each building, or portion thereof, that reflects unique hazards, sanitation, egress, and
other code related parameters associated with that category. For example, off ice
buildings fall into the Group B occupancy category, and have to meet the IBC
requirements specif ic to that occupancy. Many buildings have more than one occupancy
type on a floor or multiple floors. This is another aspect of building design that sometimes
requires f ire separations, and is again a design option, as it is possible to design the
building without separating the occupancies. Table 508.4 presents a matrix in which f ire
separations are presented between two different occupancies. This table is reproduced
below:
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In order to use this table, select the f irst occupancy f rom the f irst column, and select the
second occupancy f rom one of the columns to see the separation requirement. For
example, a Group A occupancy would be required to be separated f rom a Group S-2
occupancy by a 1 hour f ire barrier if both occupancies were not sprinklered. If a building
contains two different occupancy and use group, and one use has an area of 10% or less, it
is considered an accessory occupancy to the main occupancy, and no f ire separation is
required.
Within Table 509, there is a list of incidental building uses that require separation and/or
sprinkler systems. For example, an equipment room with a gas furnace input rating of
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500,000 btuh would require a 1 hour f ire barrier separation. Every building design should
check Table 509 to see if any incidental separation is required.
Returning to the concepts of building area and building use and occupancy, the IBC limits
the size of buildings based on yet another variable, construction type. Building
construction types are def ined in Chapter 6 of the IBC and are listed as Types IA, IB, IIA, IIB,
IIIA, IIIB, IV, VA, and VB, which are listed in decreasing order of f ire and life safety (i.e., Type
IA is the safest, and most expensive, construction type). The allowable floor area of a
building is based on occupancy and use type, construction type, sprinklering, and what
borders the building perimeter. Considering only construction type and occupancy and
use type, Table 506.2 lists the allowable areas. Within the “See Footnotes” column is a
parameter listed as “NS.” This would be the row to consult for a given construction type to
determine the building’s allowable area. For a Group A-3 building of Type IIIB
construction, the allowable area is 9,500 square feet. The top of Table 506.2 is shown
below with the correct area circled.
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If a building designer desires to have a larger building without upgrading the construction
type and without installing sprinklers throughout the building, they would be required to
use f ire walls to separate the building into, building code wise, two separate buildings.
Note that “f ire walls” is a specif ic type of rated wall different f rom f ire barriers, f ire walls
(loosely spoken without regard to the actual def inition), and f ire partitions. Fire walls
require an independent foundation such that collapse of the building on either side of the
f ire wall does not cause collapse of the other building or the f ire wall itself. Fire walls
generally require parapets, which are basically extensions of the wall above the roof line.
For our Group A-3 building, which could be a church or gymnasium, the required f ire wall
would have to have an hourly f ire resistance rating of 3 hours per Table 706.5. With a
single f ire wall, the building area could double to 19,000 square feet. While this sounds
advantageous, there are limitations in how f ire walls can be penetrated with doors and Privacy - Terms
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other openings, and the building designer would effectively be prohibited for having an
overall building with a totally open floor plan.
This article covered the f ive basic reasons within the IBC for when f ire separations with f ire
barriers or f ire walls is required. There are other instances where f ire resistance rated
construction is required within the IBC. Some of these instances are for special cases (e.g.,
atrium separation f rom the rest of the building), but others can be generalized as:
1. Fire barriers for horizontal exits
2. Fire partitions for corridors
3. Fire barriers for shafts
4. Smoke barriers for smoke control systems
5. Smoke partitions for smoke control systems
6. Smoke tight construction for incidental use separation
This article did not cover the actual construction requirements of the f ire resistant rated
construction itself. These requirements can be found within Chapter 7 of the IBC.
Construction requirements are detailed within Chapter 7 and specif ic construction related
to specif ic hourly ratings can be found in Chapter 7. Other than within the IBC, Nationally
Recognized Testing Laboratories (NRTL) publish tested and rated assemblies for designers
to use in their buildings.
Because of the numerous instances where f ire separations and f ire resistance rated
construction is required within buildings, a qualif ied professional should be consulted
regarding these requirements for any building project.
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-John P. Stoppi Jr., PE, FPE, MCP is an architectural and f ire protection engineer as well as
a fully certif ied construction code off icial
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