Clarifying the Difference Between Fireblock and Firestop¹

Until recently, most of the United States used the term "firestopping" interchangeably with "fireblocking" or "draftstopping" when describing two different construction objectives. However, it is important to understand the significant difference between a "Fireblock" and a "Firestop".

The practice of protecting penetrations that pass through a fire-rated assembly from one compartment to another was, and still is, referred to in the construction industry as "Firestopping". From the mid 1980's on, protecting through-penetrations (firestopping) has evolved into a performance-oriented discipline, which was reflected in the building codes through the adoption of test method ASTM E-814, the "Test Method for Fire Tests of Through-Penetration Fire Stops".

On the other hand, protecting against the possible spread of fire within the cavities or concealed draft openings in wood frame construction has been addressed in the codes by subdividing large concealed spaces and smaller spaces inside the stud walls, at soffits and drop ceilings and at the top and bottom of stair stringers, etc. with "fireblocking" and "draftstopping". Unfortunately, confusion has existed due to vague code language, and to the misuse of the term "firestop" to describe different construction practices. Firestopping and fireblocking are still essentially the same in some people's minds. But they are clearly different. Fortunately, changes were made in the building codes to help clarify the intent and meaning and to distinguish one practice from another.

"Fireblocking" is now defined as generic materials, such as 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. Fireblocking is used to subdivide or block off the stud cavity inside a wall, in a soffit over cabinets, and between stair stringers at the top and bottom of a run.

It is important to recognize that there is currently no specific performance test for fireblocks. Historically, the term "noncombustible" has been used. Reason would dictate, however, that in combustible construction it is not logical to require noncombustible fireblocking materials on items that do not transfer heat, such as plastic DWV plumbing pipe that penetrates a wood top plate drilled to provide a tight fit. Consequently, the current International Building Code (IBC) and International Residential Code (IRC) both have eliminated the "noncombustible" requirements pertaining to fireblocks and are revised to read "approved material to resist the free passage of flame and the products of combustion". The authority having jurisdiction may determine that the narrowest interpretation of the word "noncombustible" (as in accordance with ASTM E-136) may not be necessary at every location.

The manufacturer has worked closely with the International Code Council (ICC) and third party independent fire testing labs in order to evaluate and approve the use of Handi-Foam One-Component Polyurethane Foam for specific fireblock applications. Only those foam manufacturers that carry an ICC-ES evaluation report assuring that the product has been evaluated by the International Code Council should be considered as a suitable fireblocking material. This product has that evaluation.

1 Source: V.J. Lovell, "An Overview of Firestopping and Fireblocking: What's the Difference?", 2001.

This information is provided as a service, and is not necessarily meant to reflect any recommendation, guideline or position of The Association for Better Insulation. Each individual user must determine product suitability for any particular purpose.

Firestops and ASTM E-814 (UL 1479)......................... ..

Polyurethane foam is an organic plastic polymer. Therefore, it is combustible and will burn in the presence of sufficient heat, ignition, etc. With the addition of flame retardants, PU foams can be formulated to pass flame spread tests (i.e. ASTM E-84) which measure their resistance to combustion when exposed to an open flame. However, polyurethane foam is not intended to be used by itself as a fire stop material, according to current accepted U.S. model building codes, such as ICC, NFPA, etc., which specify that through-penetration firestop materials be tested according to ASTM E-814 (UL 1479). In order to pass firestop testing as the sole material being tested (no composite structures), a material must essentially be non-combustible, which is clearly not the case for PU foams.

ASTM E-814 (UL 1479) is a large scale fire test which evaluates a complete 'through-penetration' assembly for it's ability to withstand exposure to flame, heat and a subsequent water hose stream (to simulate a real-world fire hose situation). Each tested firestop assembly will specify the type of floor or wall that is penetrated (e.g. concrete, steel, framing, etc.), as well as the penetrating item (e.g. metal conduit, plastic pipe, electrical tubing, etc.) and also the fill material (e.g. foam, mineral wool, E 136 fireblock, etc.). Each tested system is assigned an "F Rating" (an hourly rating indicating how long the assembly will withstand the passage of flame, along with a successful hose stream test), a "T Rating" (an hourly rating indicating how long the assembly will prevent a pre-determined temperature rise on the back side of the assembly, along with a successful hose stream test), and sometimes an "L Rating" (air leakage) and a "W Rating" (water leakage). The hourly ratings apply only to the complete system. The individual components are not assigned ratings and are not intended to be interchanged between systems. Additionally, the substitution or elimination of components required in a system should not be made unless specifically permitted.

One-component foam (OCF) that has been tested to ASTM E-814 (UL 1479) requires the additional use of an inorganic material, such as mineral wool, in order to achieve any of the above hourly ratings. Any use of these products in a through-penetration firestop must be done according to an approved system assembly, and with the approval of the Authority Having Jurisdiction (AHJ—in other words, the local building official).

This information is provided as a service, and is not necessarily meant to reflect any recommendation, guideline or position of The Association for Better Insulation. Each individual user must determine product suitability for any particular purpose.

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