The material in the Steel Framing Alliance’s “A Guide to Fire & Acoustic Data for Steel Floor, Wall & Roof Assemblies” was prepared as a reference for fire and sound rated cold-formed steel framing assemblies. The purpose of the guide is to amalgamate fire and sound data for cold-formed steel floor, wall and roof assemblies that are relevant to residential and light commercial construction, thereby making it easier for steel framing professionals to find and specify a fire- and sound-rated assembly saving them time and money. The guide functions as a directory of both generic and proprietary floor, wall and roof assemblies that have been tested or listed by North American agencies.
These agencies include Underwriters Laboratories Inc., Underwriters’ Laboratories of Canada, the Gypsum Association, the National Research Council of Canada, and Factory Mutual Research (FM). An architect, engineer or others in the building industry that need an overview of the available cold-formed steel framing assemblies can simply download the guide from the Steel Framing Alliance Web site at www.steelframing.org. The Web site also provides an online search feature that can be used to quickly find listed assemblies using specific criteria.
As shown by the table of contents, the guide’s layout consists of four main sections that group the floor/ceiling, non-load bearing wall, load bearing wall (structural) and roof/ceiling assemblies. Within each section, for example floor/ceiling assemblies, the assemblies are subdivided further into the different North American testing/listing agencies (i.e., UL, ULC, GA, FA and NRCC) where the assemblies are shown in descending order as per their alphanumeric designator, e.g., UL’s U423 is followed by UL’s U424.
Figure 1 shows a typical page from the guide that provides a brief description of the tested assemblies in the form of a simple AutoCAD drawing and descriptive text. The listed assemblies’ alphanumeric designator appears in the first column, followed by text describing the assembly in the second column. The third column contains the AutoCAD drawing that shows a simple cross-sectional view of the assembly. The assembly’s hourly fire resistance ratings and acoustic data appear below the drawing. This offers a user only a brief description of the tested assembly and users are cautioned in the guide’s disclaimer to review the source documents of the testing agencies for a full description of the assembly. The second column’s descriptive text overviews the assembly’s main components that include the cold-formed steel joist, stud or truss system, fire protective gypsum membrane layer, insulation, resilient channel, and in the case of floors the wood subfloors or steel deck/concrete toppings. In regards to the cold-formed steel stud, joist or truss system if it is proprietary, the guide notes this by showing the word “proprietary” in bold followed by the product producer’s name. Guide users are cautioned in the disclaimer that assemblies constructed with proprietary products may not be available in all geographical areas.
TWO SOUND RATING SYSTEMS
Acoustic data for floors is given by two sound rating systems, Sound Transmission Class and Impact Insulation Class. STC rates the effectiveness of both floors and walls as barriers to airborne sound (i.e., the sound from sources like voices, TV sets, stereos, etc.) and the greater the STC value, the less sound is transmitted through the floor or wall. IIC rates the effectiveness of floors at reducing the transmission of impact sound hence acoustic data for walls only considers STC. IIC is strongly influenced by the finish layers on the floor, i.e., carpet, parquet, etc. As with STC, the greater the IIC value the less sound is transmitted through the floor assembly. Regulatory building code authorities typically consider a STC (or IIC) greater than 50 to be acceptable for a building’s wall and floor assemblies.
The acoustic data below an assembly’s drawing is on occasion missing. Where data exists, the STC or IIC entry has been footnoted to indicate the acoustic testing agency’s acoustic test reports, e.g. RAL-TL69-42 is a test report from Riverbank Acoustical Laboratories and SA910507 is a test report from Shiner & Associates. These test report numbers are provided in the “source” or first column below the fire testing agency’s fire design listing.
Some STC and IIC values appear with an asterisk that denotes an “estimated value as per Warnock (2005),” a footnote on the bottom portion of each page where such a value is given. The September 2006 edition of the guide featured these estimated values and follows up on the Warnock (2005) report prepared for SFA to enhance the guide with more acoustic data. The report also surveyed the existing published acoustic test reports mentioned above and referenced in the source column. The acoustic estimates are based on acoustic modeling software called “SOCRATES – the SOund Classification RATing EStimator.” The software was developed by Dr. Alf Warnock at the Institute for Research in Construction of the National Research Council of Canada. Dr. Warnock developed equations to estimate sound ratings in SOCRATES using multi-variant regression analysis, based on an analysis of the results from several large sets of measurements (174 joist floors, 117 non-load bearing walls, 39 load bearing walls and 48 double stud walls) made at IRC-NRCC.
SOCRATES allows users to perform acoustic estimates for floors and walls after selecting sub-floor materials, framing and gypsum membrane details, resilient channel spacing and type of sound-absorbing insulation material for common floor and wall assemblies. Users can download SOCRATES from NRCC via the following webpage:
Further information on “SOCRATES” is also available via the following Web site:
The data from SOCRATES (estimates provided by NRCC’s Alf Warnock) as well as data from existing acoustic test reports provides designers with additional values to consider, as more and more multi-family and other projects consider acoustic performance essential to a successful project.
LOAD RESTRICTED FACTOR
UL floor and load-bearing wall designs using cold-formed steel joists and studs can now be used for Canadian applications without a load restricted factor. Details regarding restricted load use conditions have been added to the Guide Information Pages BXUVC, Fire Resistance Ratings (Guide No. 40 U18) in the ULC Directory-Fire Resistance and BXUV7, Fire Resistance Ratings-CAN/ULC-S101 Certified for Canada in the CUL Directory. In essence, UL assemblies evaluated with loading computed in accordance with working stress design methods are identified as such and can be used in Canada under load less than specified by the limit states design methods. The percent load reductions for typical assemblies are based upon loading calculated in accordance with the working stress design method as compared to loading calculated in accordance with the limit states design method.
Working with UL and Underwriters’ Laboratories of Canada, SFA and AISI were successful in their efforts to develop a LRF of unity for load-bearing cold-formed steel wall assemblies and floors listed in UL’s directory. SFA and AISI staff were successful in convincing UL and ULC that the ratings for floors supported by cold-formed steel joists, and walls supported by cold-formed steel studs should not have a “Load Restriction Factor” because the associated loads in Canada and the U.S. are based on the same standard: CSA S136-07 or ANSI/AISI S100-07, “North American Specification for the Design of Cold-Formed Steel Structural Members.”
With an LRF of unity the UL rated load-bearing wall assemblies can now be used in Canadian building code jurisdictions. Prior to this development, only assemblies that were ULC rated were readily accepted, and because very few tested assemblies were listed in their directory, cold-formed steel faced a significant barrier to entry into the mid-rise construction segment. With the development of this LRF, about 30 UL fire-rated load-bearing wall assemblies can now be used in the Canadian market. This LRF can only be applied to load-bearing wall assemblies tested with steel braced designs, which account for the majority of UL listed assemblies.
Therefore, for use in Canada, a LRF of 1.0 (no restriction) can now be applied to UL fire rated cold-formed steel, load-bearing wall and floor assemblies. In comparison, a more conservative factor of 0.82 and 0.65 must be applied to wood framed walls and floors respectively.
For more detailed information, please refer to UL’s Web site (www.ul.com) and open “BXUV7.GuideInfo” (on the left column of its homepage, click on “Certifications”, then enter BXUV7 in the “UL Category Code” box and click search, then click on the “link to file” BXUV7.GuideInfo).
The current 7th version of the guide contains 209 fire rated floor, wall and roof assemblies (88 pages) and has grown steadily in content since originally published in August 2003 (41 pages). By working with industry, the latest information available is included in the guide with updated versions on an annual basis. The 6th version in September 2006 involved a substantial increase in content when a decision was made to include a new chapter for roof/ceiling assemblies that were predominantly proprietary truss systems. The move from being a generically based guide to including proprietary pre-fabricated cold-formed steel truss systems for roof/ceilings led to the inclusion of other proprietary floor and wall assemblies in the guide. Figure 2 gives a summary of assemblies now in the guide. The next version of the guide was planned for December 2008 with approximately 30 additional assemblies bringing the total of assemblies to 240. W&C
1 - Warnock, A.C.C., Estimation of Sound Transmission Class and Impact Insulation Class Rating for Steel Framed Assemblies, Report No. B3436.1, Institute for Research in Construction, National Research Council of Canada, Ottawa, Ontario, Canada, December 2005.