Fireproofing, Firestopping and FIREBLOCKING (Part 4 of 4)

Posted on 1/8/2018 4:17:07 PM By Sharron Halpert

We have all been on a construction project and heard someone talk about fireproofing something when they mean firestop, or firestop when they mean fireblock.  This is the final segment of our four part series, where we look at the difference between Fireproofing, Fire Blocking and Firestop.  We have examined what they do, why they are needed and what materials can be used, so that you may better understand the differences.  Now, it’s time to tackle this last one – FireBlocking

As defined by ASTM C1852, “Fireblocking is the restriction of hidden fire and smoke movement via the inside of a hollow concealed spaces in wood framed walls. Contrast this to firestopping, which is the prevention of fire spread from one side over to the other side of a fire rated wall or floor assembly.  Fireblocking is typically accomplished by the construction of a top plate (usually a 2 by 4) and the vertical wood studs in the wall.  Gaps in the plates or studs that accommodate wiring or piping could allow the free passage of fire and smoke, and should be sealed with an approved material…“When foam materials are used as a fireblock, one should ensure that they are tested in accordance with ASTM E84.  One Component Foam Manufacturers typically test to E84 using three ½” or ¾” beads of foam the length of the cement board where the test samples are placed.  This test only looks at the material and the impact fire has on how fast fire grows on a sample and how much smoke is produced. This is not to be confused with ASTM E814 for firestop through penetrations, which tests the use of the material in a variant of different scenarios.

As discussed in the standard noted above, fire and smoke will travel in the area of least resistance. When it gets into a wall, ceiling or attic; it can spread inside these cavities.  Fireblocking prevents or at least slows the spread of fire.  The areas outside of these rated cavities are required to be protected with fire sprinklers.  If a fire gets inside a gypsum wall with no fireblocking, it can spread unfettered in an area that the fire sprinklers are unable to impact. A fire in NJ lead to changes in the building codes to increase sprinkler coverage in some of these areas and increased awareness of proper fireblocking within the inspection community.

The building codes require fireblocking in walls, horizontally every 10 feet and at floor and ceiling levels; also at soffits, ceilings, attics, as well as at the top and bottom of stair runs. This will help restrain a fire from moving rapidly within the areaor from migrating to other connected concealed spaces. Don’t be confused however, a penetration through a rated assembly will require firestop materials be installed.


If you have been following this blog series, then you already know there are specific test standards for fireproofing, firestop through penetrations and firestop rated joints. Fireblocking is different though. There are no test standards specific for fire blocking (see chart below).  Instead, the code lists acceptable materials and the standard lists alternate tests that can be used to help a building official or an architect approve a foam material for use as a fireblock material as a potential alternate to the items listed in the building code.  There are no prescribed installations depths as there are with fireproofing or firestopping. This places more onus on the architect and jurisdictional inspector who are responsible to approve the materials, as well as the installation.  The building code has listed materials, such as those noted, but it is by no means an all-inclusive list.

One other difference is that firestop is installed in rated assemblies. Fireblocking is required in both rated and non-rated assemblies. This is where it gets confusing because in this article, if the floor shown in the photo is a single-family residence, then the floor is not rated and fire blocking can be used. The article explains the difference between fireblocking and draft stopping. The photo shows an example of what should be a non-rated floor using foam as a fire block.  If these penetrations were through a rated floor, firestop would be required and the material used would not be sufficient, unless there is a listed detail from a third party testing agency like UL, Omega Point and others.

Materials that are often allowed as fireblocking include lumber, structural wood panels, gypsum board, cement fiberboard, or particleboard, batts or blankets of glass or mineral wool installed within concealed spaces to resist, or block, the migration of fire and hot gases for an undetermined period of time. A complete list can be found in the International Building Code, section 718 on Concealed Spaces.In recent years, various manufacturers have developed foam materials that can be used to seal the edges of framing members to help reduce the risk of fire spread. ASTM C1852 details the third party tests that can be conducted to approve a foam based material for such an application. (list provided below)

Let’s take a moment to recap the information presented in the last four blog posts. A few things I hope you remember:

Fireblocking is for slowing fire spread inside assemblies, both rated and non-rated. 

Firestopping is for connecting two rated assemblies such as a gypsum wall to a concrete deck or for allowing penetrations through rated assemblies while still maintaining the fire rating of the assemblies. This can be either the protection of a penetration through a rated assembly or as a means of connecting two rated assemblies with a rated joint.

Fireproofing is intended to help maintain the structural integrity of steel or concrete during a fire.

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ASTM C1620- Standard Specification for Aerosol Polyurethane and Aerosol Latex Foam Sealants

ASTM C1642- Standard Practice for Determining Air Leakage Rates of Aerosol Foam Sealants and Other Construction Joint Fill and Insulation Materials

ASTM C1643- Standard Test Method to Measuring the Post Dispensing Volumetric Expansion of Aerosol Foam Sealants

ASTM E814- Standard Test Method for Fire Tests of Penetration Firestop Systems

ASTM E84- Standard Test Method for Surface Burning Characteristics of Building Materials

UL1715- Standard for Fire Test of Interior Finish Material

UL723- Standard for Test for Surface Burning Characteristics of Building Materials