This is coming from an interior closet?
Is the utility closet sealed from the interior? If so, it is the fire stop.
What is the fire spread rating for flex duct? The duct must be metal if you need to seal the opening. Flex won’t cut it.
BUILDING CODE REQUIREMENTS
Marketing Development Manager for Fire Protection Products
Vickie J. Lovell
Building Code Consultant
The 2003 International Building Code (IBC) and 2003 International Residential Code (IRC)*
have established a means by which fire spread can be controlled within void spaces created
within wood framed assemblies: fireblocking.
During a fire, flame and heated products of combustion can spread via paths of least resistance.
Certain assemblies, particularly wood frame assemblies, result in concealed voids or cavities
within walls, ceilings and attics, which not only affect the spread of fire, but also make
suppression more difficult.
Fireblocking involves the use of field-installed building materials to prevent the movement of
undetected flames and gases to other areas through such concealed spaces. Although such
materials are not required to be tested for fire resistance, they are to be installed to slow fire
migration, and to contain a fire until it can be suppressed.
Fireblocks should not be confused with firestops. Firestops are required by the codes when a
higher degree of fire protection is required, particularly when penetrations through fire resistance
rated assemblies are to be protected with a specific assemblage of materials that have been tested
under severe fire conditions for a prescribed period of time. Unlike fireblocks, the purpose of a
firestop is to prevent the spread of fire from one compartment to another through service and
utility openings in floors, ceilings, roofs, and walls.
Fireblocks are required between floors, between a top story and a roof or attic space, in furred
spaces or the cavities between studs in wall assemblies, at connections between horizontal and
vertical spaces created in floor joists or trusses, soffits, drop or cove ceilings, combustible
exterior wall finishes and architectural elements, and at openings for pipes, vents, ducts,
chimneys, and fireplaces.
Fireblocks conform to innumerable configurations, depending on the dimensions and location of
the concealed space. Section 717 of the IBC is a dedicated section that provides the description of
concealed spaces and fireblocking. Section 717.2.1 identifies the materials that are acceptable for
use as fireblocks. Fireblocks can be constructed of materials such as 2 inch nominal lumber,
structural wood panels, gypsum board, cement fiber board for larger fireblock, and batts or
blankets of mineral wool or glass fiber, loose fill insulation, and caulks, sealants, and putties for
smaller fireblocks. Similar text appears in the IRC.
Frequently, and inevitably, pipes, vents, ducts, and similar items penetrate fireblocks. The IBC
requires that the integrity of the fireblock be maintained in 717.2.1. This may be accomplished by
using an sealant, caulk or putty as permitted by 717.2.5. Such materials are required to be
approved for such use, and may be either combustible and noncombustible per the specific code
section and application. The use of a noncombustible sealant would address both conditions
where either combustible or noncombustible are required, but not vice versa. Therefore, a
noncombustible material would serve a broader range of uses than a combustible sealant, caulk or
putty. (Noncombustibility shall be determined by testing to ASTM E 136 per other sections of the
All chimneys and fireplaces are required to be fireblocked by the code. Factory-built chimneys
and fireplaces are required to be fireblocked by the code, but are also required to be tested in
accordance with UL 103 and 127. Those test methods contain specific information pertaining to
fireblocking beyond the code requirements.
As a side bar, the IBC also requires the use of such noncombustible sealants in other locations
that are not related to fireblocks, but serve a similar purpose, such as small metallic membrane
penetrations within certain size restrictions in section 712.3.2, exceptions 1.3 and 2.2 In
penetrations of non-fire resistance rated assemblies, the IBC permits both combustible and
noncombustible sealants to be used to limit the migration of fire and the products of combustion.
The sealants used to protect noncombustible penetrations that connect not more than three stories
in section 7188.8.131.52 are required to be noncombustible. 7184.108.40.206 permits any approved sealant on
any type of penetration provided that the penetration does not connect more than two stories.
In all building codes, the designs and location for fireblocking are required to be indicated on the
construction documents, and are subject to inspection before occupancy in new construction.
- The IRC is a building code for 1 and 2 family dwellings. All other construction, including all other types
of residential housing regardless of construction type, falls under the IBC.
In addition to the requirements of IBC Chapter 717 for fireblocking, the following
are other locations where fireblocks are used in the 2003 International Building
705.7 Noncombustible fireblock required where combustible framing intersects into hollow
spaces of masonry or concrete fire wall.
Shaft requirement may be eliminated for chimneys when fireblocked
708.4 Fireblocking required in fire partitions when not continuous between deck and ceiling
Interior finish (paneling over furring strips)
804.4.1 Subfloor construction
1406.2.4 Combustible exterior wall veneers
Fireplace clearances and fireblock requirements.
Chimney clearance and fireblock requirements.
*The International Mechanical Code (IMC) contains similar requirements for chimneys and fireplaces and
has a number of locations where it prohibits penetrations through fireblocking. However, where
fireblocking is permitted, the IMC refers the to International Building Code for compliance.
In addition to the requirements of the IRC Section R602.8 for fireblocking, the
following are other locations where fireblocks are used in the 2003 International
Residential Code, the International Residential Mechanical Code, and the
International Fuel Gas Code
R502.13 Wood frame construction required to be fireblocked
R602.4 Interior load bearing and non load bearing walls to be fireblocked same as
Chimney clearance and fireblock requiremets
Fireplace clearances and fireblock requirements
M1601.3.3 Duct installations shall be fireblocked
M1801.9 Chimneys and vents shall be fireblocked
G2425.15.4 Chimneys and vents (using fuel gas) shall be fireblocked
Your local code may or may not adopt this code. You need to check if your going to try to enforce it.