Research from the Institute for Research in Construction found certain types of gypsum board — depending upon how much is used, how it’s attached and the characteristics of the material it’s attached to — can improve fire resistance.
Specifically, the research found:
o Type X gypsum board plays a key role in the fire resistance of floor assemblies, as it is the first line of defense in protecting framing and subfloors. To improve the fire resistance of floor assemblies, 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 number 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.
o A second layer of gypsum board added to a floor assembly with only one layer of Type X gypsum board provides more fire resistance than the addition of a second layer of sub-floor.
o Concrete topping added above the subfloor slightly increases fire resistance.
o An increase in live load decreases fire resistance.
o Floor assemblies with either rock-fiber or cellulose-fiber insulating material provides more fire resistance than those with glass-fiber insulating material.
The research is part of the institute’s and a group of industry partners’ efforts to complete the second phase of a comprehensive collaborative project that will provide 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.
In this second phase, fire researchers sought to confirm some of the findings of the first phase of research. It sought to find out the way support conditions as well as the type of insulating material used and its method of installation 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, fire resistance ratings improved dramatically. Both findings are related to the issue of keeping the insulating material in place longer.
In the second phase, acoustics researchers also set out to resolve some inconsistencies in results from the first phase of the project. In particular, the results were unclear as to whether whether different types of insulating (sound-absorbing) material, such as rock, cellulose and glass fiber — gave consistently different sound transmission ratings in otherwise identical floor systems..
In this second phase, measurements of airborne and impact sound transmission were made through approximately 60 floor assemblies. The analysis of the combined data from both phases of the project led to a better understanding of the factors that influence sound insulation, showing that:
o In practice, the thickness of Type X gypsum board used in the ceiling does not affect the sound transmission class ratings significantly.
o The type of insulating material sometimes changed the sound transmission class ratings and other times did not; the conclusion being that it is not an important factor for determining these ratings.
An important additional outcome of the second phase of research is a program for estimating sound transmission class, impact insulation class, and some related ISO ratings, which were developed for floors with resilient metal channels and insulating material. The presence of both of these elements was clearly shown to be essential for achieving high sound transmission class ratings, with minimum-weight assemblies.
