Authors: Mark St. Onge, Lead Field Engineer, UL Solutions
Swati Tyagi, Manager Industry Marketing, UL Solutions
The concern
A current trend at construction sites is fire resistant-rated assemblies being constructed so they connect to unprotected steel members, either at the horizontal head of wall (HW) joint or the vertical joint where the wall connects to a column. Fire resistant-rated walls that connect to the bottom flange of an unprotected structural steel member are one common example. In this instance, a concern would be the inability to install a fire resistance-rated head of wall joint at the top of the wall assembly. A joint system installed between two assemblies with different fire-resistance ratings can only be rated to match the lower of the two. If any component, such as a steel member, is left unprotected, its fire-resistance rating is effectively zero. As a result, the entire joint system would also be rated zero hours, failing to meet model code requirements that mandate the fire-resistance rating be continuous from the floor through to the floor or ceiling above.
Secondary concerns
Another concern with this type of construction is that the joint systems used are often not compliant with UL 2079, the Standard for Tests for Fire Resistance of Building Joint Systems. UL 2079 specifically evaluates joints installed between two fire-resistance-rated assemblies. It does not address conditions where one of the assemblies, such as an unprotected steel member, lacks a fire-resistance rating.
A similar scenario is seen when a rated wall terminates at the underside of a non-rated floor or ceiling assembly. In such cases, UL Solutions testing is conducted with a rated floor assembly to isolate the performance of the joint system from the potential failure of the non-rated floor. These tested systems are published under the product category XHBO – Continuity Head-of-Wall Joints in the UL Product iQ® database, which is free to use but requires a one-time registration.
Model codes
NFPA 101, Life Safety Code®, and NFPA 5000, Building Construction and Code®, do not allow fire resistance-rated joints to be installed between the wall assembly and an unprotected steel beam. These model codes include a reference to NFPA 221, which explicitly prohibits this condition.
NFPA 101 should be a common reference in all construction documents, as it is typically enforced at healthcare occupancies regulated by CMS/Joint Commission.
NFPA 221 section 7.2.4 states, “The fire barrier wall shall be permitted to terminate at an individually protected structural member in the same plane, provided the structural member has a fire resistance rating of not less than that required for the fire barrier wall.”
The International Building Code (IBC) requires continuity of the wall assembly, which extends from the top of the floor/ceiling assembly below to the bottom of the floor above. Unprotected steel members do not comply with this requirement because they would allow the temperature on the unexposed side of the assembly to exceed the maximum temperature allowed by UL 2079 (ASTM E1966).
While the importance of protecting structural steel may seem straightforward, confusion often arises due to an exception in the IBC that allows certain supporting structural steel members to remain unprotected. This exception is frequently used as a cost-saving measure, but it can lead to noncompliance and misinterpretation of fire-resistance requirements, especially when joint systems are involved. As a result, the lack of protection can compromise the structural integrity of the fire-resistance-rated assembly and create challenges in meeting code requirements.
Test standards
To illustrate why unprotected steel members would fail the fire test in UL 2079, it is necessary to understand how the fire testing is performed.
Fire testing for the joint is conducted in compliance with UL 2079. During the fire testing, thermocouples are placed at specified locations on the non-fire side of the test assembly, not directly exposed to the fire. One location of thermocouple placement is at the head of the wall and would be on the back side of the unprotected steel member. The pass/fail criteria for the temperature rise of thermocouples are exceeding 325 degrees Fahrenheit, plus the ambient temperature of the room during the test. The temperature is increased via the gas-powered furnace in accordance with the standard time temperature curve in UL 2079. In the fire test, the temperature of the unprotected steel will rise on the unexposed side, and the heat at the head of the wall location will be significant.
3.1.1 The conduct of fire tests of materials and construction is to be controlled by the standard time-temperature curve shown in Figure 3.1. The points on the curve that determine its character are:
a) 1000 F (538 C) at 5 min
b) 1300 F (704 C) at 10 min
c) 1550 F (843 C) at 30 min
d) 1700 F (927 C) at 1 h
e) 1850 F (1010 C) at 2 h
f) 2000 F (1093 C) at 4 h
g) 2300 F (1260 C) at 8 h or over
Current certifications
The UL product category for certified (listed) head-of-wall fire-resistive joint systems is XHBN. These systems are tested with the structural steel protected, and the listings typically specify the use of spray-applied fire-resistive materials (SFRM) or intumescent fire-resistive materials (IFRM) to achieve the required fire-resistance rating.
A critical aspect of compliance is ensuring that the materials used match those specified in the UL Listing and the manufacturer’s installation instructions. SFRMs can be formulated with various materials and proportions to deliver specific hourly ratings. Therefore, the entire system must be tested as a unit to evaluate essential performance criteria such as sealant bond strength, movement capabilities and fire containment integrity.
Some certifications specify a particular manufacturer’s product, while others allow for generic product types, such as “cementitious fireproofing” or “spray fiber fireproofing,” which permit the use of any product within that category that meets the required rating.
Education and awareness
To ensure proper application and code compliance, it is essential that code authorities, design professionals and contractors understand:
- The model code requirements for fire-resistive construction
- The complexities and limitations of system listings
- The importance of following manufacturer instructions
Ongoing education and training programs are critical to building the competency needed to achieve reliable fire containment and code-compliant construction.
Plan review and field inspections
Firestopping compliance, especially for joint systems, can be challenging during plan review and inspections. Construction documents often include only general references to listed systems without specifying the exact listing required for each application.
To help ensure code compliance:
- Code officials should request that design professionals provide specific listed systems as part of the construction documentation.
- Field inspections should verify that the installed systems match the listed details, including materials, dimensions and installation methods.
Properly constructed, installed and maintained listed assemblies and systems are the foundation of code-compliant, fire-resistive construction. These principles are further detailed in the UL Solutions Firestop and Joint System Application Guide.
For more information, visit The Code Authority or contact UL Solutions at: fire.inspection@UL.com