Head-of-wall firestopping systems are tested to ASTM Standards and listed by accredited third-party laboratories such as Underwriters Laboratories, Omega Point Laboratories and Intertek. All of the information needed to properly select and install the firestopping system is provided in the third-party listing. The following paragraphs provide information about proper selection of head-of-wall firestopping listings and installation of fire resistive joint systems with some common misconceptions.

Ratings game

Typically, the listing header contains the listing number, the fire resistance rating, the maximum joint size and its movement capability provided as a percentage of the joint size. The movement percentage for compression and extension indicates the amount of movement an installed assembly can accommodate. For example, a 1-inch installed joint protected with a listing capable of 25-percent movement in compression and extension is capable of a 1/4 inch of movement up and down at the specified fire resistance rating. Movement outside this range would compromise the materials in the joint and negate the fire rating.

The architectural specifications always require a gap at the top of wall to accommodate anticipated floor or roof deflections. This gap is intended for all walls, both rated and non rated. Design professionals often misconceive that all listings are capable of a 100-percent movement. A common mistake is made when a 1/2-inch joint is installed for all rated and non-rated walls to meet the specification when the listing used is only capable of a fraction of that joint size. It is extremely important that the actual movement capability of the installed system is equal to or better than the required joint movement capability provided by the design professional and/or structural engineer.

The wall and floor/roof construction allowed by a system is specified in the head-of-wall firestopping listing. The minimum requirements in this section of the listings should match the field conditions. The following require special attention:

• Ensure that the fire protection material on the floor/roof assembly or beam/joist (if applicable) in the field condition is listed in the system. Currently, head-of-wall firestopping systems at Underwriters Laboratories are available for only cementitious fire resistive materials. There are no head-of-wall firestop listings allowing the use of mineral fiber fireproofing.

• Ensure the actual wall assembly in the field condition is accommodated by the system. Shaft walls that are installed from one side of the wall and incorporate a gypsum liner or core board are different than standard steel stud walls and should be specifically listed in the system.

Standard procedure

A condition that is prevalent in most buildings is a rated wall assembly that meets a non-rated roof assembly. Finding a third party listed system for this condition is unfortunately not possible. The reason is that ASTM E 1966 "Standard Test Method for Fire-Resistive Joint Systems," the test method used by the third party laboratories, mandates that the wall and floor or roof assembly used in the test have an hourly fire resistance rating. Therefore, it is simply not possible to run a test in accordance with ASTM E 1966 with an unrated roof assembly and obtain a third party listed head-of-wall firestopping system. In these conditions, firestop systems are installed to provide a smoke seal at the joint.

Installation of the firestopping materials into the head-of-wall joint is provided in the system. If mineral wool is a component of the system, ensure the type of mineral wool and the density installed are listed in the system. Secondly, ensure the mineral wool is compressed into the joint as indicated by the system.

For example, 33-percent compression of the mineral wool would require placing a 3-inch-tall piece of mineral wool into a 2-inch-tall space. If an elastomeric coating or sealant is a component of the system, ensure the coating or sealant is applied to the required wet thickness without voids or thin spots and overlaps the adjacent assemblies as specified in the listing. Improper application of the coating or sealant may compromise the integrity of the installation and permit the passage of smoke through the opening.

Head-of-wall firestopping system selection and installation can be made simple if the tested listing is understood and utilized as a guide for proper installation. If there are specific questions about a third party laboratory listed head-of-wall firestopping system, the third party laboratory or manufacturer of the firestopping materials listed in the listing should be contacted for clarification. Proper installation of firestopping systems the first time can reduce long-term applicator expense and maintains a high level of life safety for building occupants.

More information about the International Firestop Council is available at www.firestop.org.