Author: Kevin Hyland – Principal Engineer, Fire Resistance and Containment, Built Environment
A wall assembly constructed of steel studs and gypsum board and tested for a fire resistance rating in accordance with UL 263, the Standard for Fire Tests of Building Construction and Materials (ASTM E 119, Standard Test Methods for Fire Tests of Building Construction and Materials), is one method recognized by model codes to achieve compliance with requirements for fire resistance. If the test is successful and establishes an hourly rating, the gypsum board is placed under UL certification and UL Solutions Follow-Up Services and is eligible to bear the UL certification Mark for fire resistance. In some instances, the steel studs may also be included. UL fire-resistance-rated wall assemblies include specifications summarizing the necessary materials and construction methods to achieve the fire rating. You can easily access this information in UL Product iQ®, which is available to use at no cost but requires a simple one-time registration.
These steel stud and gypsum board wall assemblies (designs) can be found in the U400, V400, W400 and newly established U4100 series on Product iQ. This article, and a recent addition to the Walls and Partitions section in the BXUV Guide, clarify the need for certification.
When steel studs must bear the UL certification Mark
A non-load-bearing steel stud wall design, such as BXUV.U465, will often include the steel floor and ceiling runners, or tracks, as Item 1 and the steel studs as Item 2. These items do not have an asterisk (*) on their item labels, signifying that these items do not need to bear the UL certification Mark (i.e., they are considered generic and do not need to be under UL certification). These generic studs and runners must only meet the shape, dimension and thickness criteria specified in the item description. For Design U465, the minimum steel thickness of the generic studs and runners is 25 gauge (ga.). The bare-metal thickness associated with 25 ga. can be found in the table of steel thicknesses in the BXUV Guide.
In the mid-2000s, the steel stud industry began to look for solutions to conserve the amount of steel used in the wall framing while maintaining the fire rating, when needed, for fire-resistance-rated wall assemblies. Some of these solutions involved steel wall studs manufactured with a bare (base) metal thickness thinner than 25 ga. steel. Before rolling into channel form, the base strip steel is altered in various proprietary ways, increasing the strength capacity of the lighter-gauge material. These studs must be evaluated for fire resistance in accordance with UL 263 (ASTM E119) since they are manufactured with steel less than 25 ga. Like the gypsum board, when the test is successful, the steel runners and studs are placed under UL certification and UL Solutions Follow-Up Services and are eligible to bear the UL certification Mark for fire resistance under the Framing Members category (CIKV).
Over time, various proprietary studs and runners (fabricated of thinner base metal) were developed and fire-tested in accordance with UL 263 (ASTM E119). The industry coined the term “EQ” studs, or “equivalency” studs, for these types of studs. Having developed the necessary full-scale fire test data, some of these proprietary studs (and their runners) were added to existing steel stud wall designs as alternates to the generic runners and studs. Since these runners and studs are certified, their item labels (for example, “Item 1A” and “Item 2A”) contain an asterisk, signifying that they must bear the UL certification Mark.
The purpose of the addition to the BXUV Guide is to clarify that when runners and studs are specified generically (i.e., without an asterisk in the item label), they do not need to bear the UL certification Mark. However, they must meet the specified minimum bare metal thickness. The proprietary studs (i.e., EQ studs) do need to bear a UL certification Mark as indicated by the asterisk and therefore need to meet the construction requirements (including bare metal thickness) found in the UL Follow-Up Service procedure.
Below is the addition to the BXUV Guide:
Many non-load bearing steel stud wall designs specify generic steel studs, characterized by minimum dimensions and thickness, and do not bear the UL certification Mark for Fire Resistance. These studs shall meet the minimum bare metal thickness as described in the table, corresponding to the minimum gauge specified for that item.
Fire tests have also been conducted on proprietary studs (commonly called equivalency studs, or “EQ” studs) where the bare metal thickness may be less than as shown in the tables above*. Where permitted, these proprietary studs are listed in the individual design, and are Certified under the Framing Members category (CIKV). These studs shall bear the UL certification Mark for Fire Resistance.