Q: Can I use a generic cold-formed steel framing profile in a UL fire resistant design?
A: The quick answer to that question is, maybe. It depends on the UL design certification itself. The individual listing will define if generic profiles can be used. The key to answering the question then becomes understanding the information contained within the individual listing. To start the discussion, UL publishes specific guidelines on acceptable variations from what was originally tested. Using the UL online certification directory as a source, at the top of each listing is a link to find out more information on fire-resistive construction. This link is entitled “See General Information for Fire-resistance ratings – ANSI/UL 263 Certified for United States Design Criteria and Allowable Variances.”
Specific to cold-formed steel framing are some key guidelines. One example of this is that the dimension and thickness of the studs shown in the listing are minimum values. That means the use of steel thickness and stud depths that are greater than what was tested and listed will not negatively impact the overall system performance. Following that same principal, stud spacing listed in a design is the maximum value. If the wall is listed with studs spaced at 24 inches on center, it is acceptable to place the studs at 16 inches on center. However, the installation cannot go the other way. If the wall was listed with framing at 16 inches on center, it is not acceptable to go 24 inches on center. The steel framing members themselves should comply with the appropriate ASTM standard. This means that nonstructural framing must be in compliance with ASTM C645, Standard Specification for Nonstructural Steel Framing Members. If the framing is structural or load-bearing, then it must meet specification ASTM C955.
The next step in understanding fire-resistance design and UL certifications pivots on the concept that a fire-resistive design is based on a system’s performance when subjected to fire-resistive testing. No single product has a fire-resistance rating. The rating applies only to the assembly comprised of the gypsum panels, steel studs, fasteners and joint treatment. Each component within a design plays a key role in obtaining the desired hourly rating. That is why when looking at a UL certification, you start with a drawing depicting each building product required in the system. UL calls each building material a construction element, and therefore each has an associated number. UL Design U411 shows four construction elements numbered as follows: (1) floor and ceiling runner, (2) steel studs, (3) batts and blankets and (4) gypsum board.
This design is for a generic two-hour wall. Item number three is listed as optional, which simply means the insulation is not required for obtaining the fire-resistance rating. What this optional status implies is that the presence of the listed insulation does not detract from the fire performance of the partition.
Item number one, as mentioned, is listed multiple times. These multiple listings are the basis in determining if a generic profile that meets the appropriate ASTM standard is allowed. In some cases, the construction element is called “Floor and Ceiling Runner” while in others it is called out as “Framing Members* – Floor and Ceiling Runner.” The asterisk has significant meaning. At the top and bottom of the individual certification is the following: “*Indicates such products shall bear the UL or cUL Certification Mark for jurisdictions employing the UL or cUL Certification (such as Canada), respectively.”
This quote identifies a proprietary product from an individual manufacturer. For building product manufacturer to receive the UL Certification Mark, they must participate in the UL Follow-up Service. This service requires that UL, on a timely basis, audits the plant where the product is manufactured to assure that what was originally tested is what is being manufactured.
The floor and ceiling runners that do not have the asterisk are defined simply as having a minimum steel thickness of 25 gauge. After that, the certification stipulates that the legs of the runner to be one inch minimum and the depth of the runner to meet the stud size.
Item two is listed as “Steel Studs” with no asterisk. Following the runner specification, the requirements for the stud are a minimum stud depth of 2 1/2 inches with a steel thickness of 25 gauge. The maximum stud spacing for this design is 24 inches on center. Also specified is that the length of the stud shall be three-quarters of an inch less than the assembly height. This is basically the definition of a generic profile. For code compliance, this generic profile should be part of a code compliance certification program such as what is required for membership in the Steel Framing Industry Association. This program can be viewed as analogous to the UL Follow-up Service.
The answer to the original question is if the desired UL certification lists the steel framing construction elements without the asterisk, then the cold-formed steel generic profile is deemed acceptable. However, final approval of this interpretation is up to the authority having jurisdiction over a project in question.
Robert Grupe is AWCI’s director of technical services. Send your questions to [email protected], or call him directly at (703) 538.1611.
