Canada's Institute for Research in Construction (IRC) and a group of industry partners have just completed the sec-ond phase of a compre-hensive collaborative project that will pro-vide major benefits to both parties and to the construction industry as a whole.
The first phase of the project, completed in 1998, led to a better understanding of the fire and acoustical performance of traditional building systems used in residential construction. Specifically, fire-resistance ratings (FRR) and noise-control ratings for 177 generic floor assemblies were added in 2002 to the National Building Code (NBC) Part 9, Appendix A. This increased number of assemblies has led to greater choice and the potential for better performance at reduced cost to designers, builders and consumers.
However, most of the new entries in the expanded table in the NBC give updated information about the acoustical performance of the assemblies but not about their fire performance. To address this defi-ciency, Phase 2 of the project was launched, with the intent of "filling in the blanks" by providing the tech-nical information necessary to deter-mine the FRRs for these assemblies as well as some others.
In this second phase, fire researchers sought to confirm some of the findings of Phase 1-those concerning support conditions, and the type of insulating material used and its method of installation-and the way they affect fire-resistance ratings. When all four edges of the gypsum board were supported and the screws set back from the edges, and when sprayed-on cellulose was used, the FRRs improved dramati-cally. Both findings are related to the issue of keeping the insulating material in place longer.
In addition, fire researchers confirmed that:
- Type X gypsum board plays a key role in the fire resistance of the floor assembly, as it is the first line of defense in protecting the framing and sub-floor. To improve the fire resistance of floor assem-blies, attention should be focused on the spacing of either the framing or the resilient channels where the gypsum board is attached, as well as on the num-ber of gypsum board layers in the floor. (The closer the spacing, the more screws used to support the gypsum board; hence the better the fire resistance.)
- A second layer of gypsum board added to a floor assembly with only one layer of Type X gypsum board provides more fire resis-tance than the addition of a sec-ond layer of sub-floor.
- Concrete topping added above the sub-floor slightly increases the fire resistance.
- An increase in live load decreases the fire resistance.
- Floor assemblies with either rock -fiber or cellulose fiber insulating material provided more fire resis-tance than those with glass fiber insulating material.
Acoustics Portion of ProjectWith respect to the acoustics portion of Phase 2 of the project, the goals were to examine areas in which information was lacking, and to obtain reliable sound ratings for spe-cific floors that had already obtained adequate fire-resistance ratings.
Acoustics researchers also set out to resolve some of the inconsis-tencies in results from Phase 1. In particular, it was not clear whether the different types of insulating (sound-absorbing) material-rock, cellulose and glass fiber-gave con-sistently different sound transmis-sion ratings (sound transmission class, STC, and impact insulation class, IIC) in otherwise identical floor systems. Also, the few results available with 12.7-mm-thick gyp-sum board had somewhat higher STC ratings than expected. While the first phase of the project was extensive, not all material variations were systematically investigated.
In this second phase, measure-ments of airborne and impact sound transmission (STC and IIC) were made through approximately 60 floor assemblies. The analysis of the combined data (from both phases of the project) led to a better under-standing of the factors that influence sound insulation, showing that:
- In practice, the thickness of Type X gypsum board used in the ceiling does not affect the STC or IIC ratings significantly.
- The type of insulating material sometimes changed the STC or IIC and other times did not; the conclusion being that it is not an important factor for determining these ratings.
Program for Estimating Assembly RatingsAn important additional outcome of Phase 2 is a program for estimating sound transmission class, impact insulation class, and some related ISO ratings, which was developed for floors with resilient metal chan-nels and insulating material. The presence of both of these elements was clearly shown to be essential for achieving high STC ratings, with minimum-weight assemblies.
The program is based on mathe-matical expressions fitted to the data from both phases of the project to predict expected values for the NRC laboratory facility. From various menus, users can select sub-floor materials, framing and ceiling details, resilient channel disposi-tion, and the thickness and type of sound-absorbing material for com-mon floor assemblies. A similar analysis was done for previous IRC projects that studied sound trans-mission through gypsum board walls. As a result, the program also includes algorithms for estimating sound transmission through this type of wall.
The beta version of the program is now available on the Web at this link.
Next StepsThe findings from this multidiscipli-nary project are being compiled and an ad hoc committee of project part-ners is preparing a submission for changes to the NBC. This code change request will be considered by the appropriate standing commit-tees after the publication of the 2005 NBC, for possible inclusion in the next edition.
For more information about the fire portion of this project, contact Dr. Mohamed Sultan at (613) 993-9771, fax (613) 954-0483, or e-mail firstname.lastname@example.org; for more information about the acoustics portion, contact Dr. Alf Warnock at (613) 993-9370, fax (613) 954-0483, or e-mail email@example.com.
Project PartnersCanada Mortgage and Housing Corp., Canadian Steel Construction Council, Canadian Wood Council, Cellulose Insulation Manufacturers Association of Canada, Cellulose Insulation Manufacturers Association (U.S.), Forintek Canada Corp., Gypsum Association (U.S.), Gypsum Manufacturers of Canada, Ontario Ministry of Municipal Affairs and Housing, Owens-Corning Canada, Roxul Inc., Truss Plate Institute of Canada, and Truss Plate Institute (U.S.).
This article was reprinted from Construction Innovation, March 2005, an industry publication from the IRC.