Understanding Fire Resistance-Rated Joint Systems

Under the 2021 International Building Code (IBC), fire-resistance-rated joint systems are required to be designed and installed in order to protect the intersections of all types of fire-resistance-rated construction.

This means, where fire-rated walls, floors, roofs, etc. intersect, these intersections must be provided an equal degree of fire protection as the assemblies they join. For example, where 1-hour-rated walls and ceilings meet, a 1-hour-rated joint system must be installed. The same goes for 2-hour and 3-hour systems, etc. In the 2021 IBC, the rules for fire-rated joints are found in Chapter 7, “Fire and Smoke Protection Features,” Section 715, “Joints and Voids.” We won’t be talking about voids in this article, but focus on the joint systems instead.

Rules for Fire-Rated Joints

Per Section 715, fire-resistant joint systems are required to be installed in or between fire-resistance-rated walls, floors, and roofs to resist the passage of fire for a time period not less than the required rating of the assemblies they join. This section also requires such joints to be tested according to ASTM E1966 or UL 2079 (which are essentially identical tests). This means the joint systems, similar to the walls and floor/roofs they are a part of, are required to undergo actual fire tests in laboratory conditions to ensure that they can perform as required to protect the building and its occupants.

ASTM E1966 establishes the expected performance of the joint systems during a fire event, and there are five criteria a fire-resistant joint system must meet in order to pass the test. These five conditions of compliance are as follows:

Fire-Resistant Joint System Criteria

Movement Cycling Test

This test ensures that the joint can accommodate thermal and structural movement during a fire event and maintain the integrity of the joint without failure during the prescribed amount of time. Since joints in between systems are some of the first portions of construction to split apart under fire conditions, the importance of ensuring the joint can accommodate this movement is understood.

Fire Endurance Test

This test, just as it sounds, is intended to ensure the joint can protect the building during fire exposure for the prescribed amount of time. Simply put, this means that the joint must be able to withstand and endure the direct effects of fire during the test time without failure.

Integrity Test

This test includes the placement of a cotton pad on the opposite side of the joint, and in order to pass this test, the cotton pad must survive the test without ignition. For example, if a joint splits apart under movement cycling and fire exposure, the likelihood that the cotton pad will ignite is much higher, since the joint split during the test. Therefore, a successful joint test will prohibit the cotton pad from igniting, thus clearly demonstrating that the joint can serve its function of protecting the building against the spread of fire and hot gases.

Load Application Test

This test is for joints protecting assemblies that are load-bearing. Fire-resistance-rated walls and partitions are commonly designated as load-bearing or non-load bearing, and the incorporation of structural loads into fire tests can affect the system and its failure methods, therefore, if a fire-rated joint is intended for load-bearing applications, the test must include the application of a structural load into the test assembly to ensure the joint can perform successfully under loaded conditions.

Hose Stream Test

This test determines how the joint will perform in an active firefighting environment. During active fire fighting operations, the amount of water and its velocity as it’s sprayed from the fire hose can damage construction materials. The joint must be able to accommodate spray from a fire hose without failure. The way this is stated in the test method is that “the fire-resistive joint system shall have withstood the hose stream test without developing any opening that permits a projection of water from the stream beyond the unexposed surface” of the joint.

Special Conditions for Dynamic Movement

If all applicable tests are passed, the joint will be assigned a UL test number and be recognized as meeting building code requirements in this regard. However, please keep in mind that while the UL does provide head/sill details in their wall tests, if a rated joint system is required with dynamic movement (like a slip head track at interior partition heads), in most cases the UL requires the head/sill details to match the joint specifications, overriding the head/sill specifications in the wall description. This is because the wall tests are focused on the wall assembly, and not specifically on the joints of the wall, so when special conditions are required for the joint (dynamic movement), the joint assembly prevails as the applicable detail.

In Conclusion

As an architect or building designer, keep in mind these important facts: (1), the fire-resistant joint systems are unique and separate systems, distinct from the rated wall/floor/roof assemblies they are protecting; (2) where the conditions described in Section 715 exist, a tested joint system is required to be specified (for example, you can’t just generically specify 1-hour rated fire caulking, it must be a tested assembly); and (3) UL details may specify when a specific joint system is necessary over the general head/sill details in any given tested assembly. Spending some time studying this section of the code, along with the UL designations, will help you better understand how to design these critical life safety systems.