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Fire and steel stud walls : stud spacing and type of insulation are just two of the factors that will affect how long a typical residential
loadbearing steel stud wall assembly can last in a fire
Kodur, V. K. R.; Sultan, M. A.
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Fire and steel stud walls: stud spacing and type of insulation are just two of the factors that will affect how long a typical residential
loadbearing steel stud wall assembly can last in a fire
Kodur, V.K.R.; Sultan, M.A.
NRCC-45662
A version of this document is published in / Une version de ce document se trouve dans : Canadian Consulting Engineer, v. 43, no. 3, May 2002, pp. 29-30
Fire and steel stud walls: stud spacing and type of insulation are just wo of the factors that will affect how long a typical
residential loadbearing steel stud wall assembly can last in a fire by V. K. R. Kodur and M. A. Sultan
Steel framing has found wide application in residential buildings in recent years. Loadbearing steel stud wall assemblies form part of steel framing and are often used as party walls in townhouses and as party and corridor walls in multi-unit low-rise construction.
Consequently, in Canada, they are required to meet fire resistance requirements.
Because there is very limited information on the fire resistance of loadbearing steel stud wall assemblies in the literature and in building codes, NRC’s Institute for Research in Construction
conducted a series of fire resistance experiments on full-scale wall assemblies to generate some reliable data. This was part of a major collaborative research project initiated with nine industry partners to develop fire resistance ratings for these and various other types of wall assemblies.
Test parameters included stud-spacing, stud rows, shear bracing, load intensity, gauge thickness, gypsum board layers,
resilient channel installation and type of insulation. Fourteen complete assemblies (whole systems, not just materials) were tested to get a complete picture of how the various parameters affect fire
performance. Parallel acoustical tests were also conducted, as the achievement of good acoustic performance may have negative implications for fire performance, or vice versa.
Experimental Program
Systems tested were replicates of wall assemblies commonly used in North America and were 3048 mm high by 3658 mm wide.2 Thirteen of the assemblies were provided with steel cross-bracing to enhance lateral resistance, while the fourteenth assembly was
provided with an OSB shear membrane. All assemblies were
protected with Type X gypsum board on both fire-exposed and unexposed sides.
The assemblies were exposed to heat in a propane-fired vertical furnace. The tests were conducted in accordance with the requirements of CAN/ULC-S101 (which is similar to ASTM E119). Fire exposure continued until the assembly failed — structurally, or by exceeding a specified temperature, or permitting the penetration of flames or gases. All wall assemblies failed structurally and the unexposed surface temperature (average of single reading temperatures) at the time of structural failure was below the temperature failure criteria.
Results and Discussion
The factors most significantly influencing the fire performance of the wall assemblies were the number of gypsum board layers, the presence of resilient channels, the stud-spacing, the number of stud rows, and the type of insulation in the wall cavity. Figure 2 shows the effect of stud-spacing on the fire resistance of the single row steel stud wall assembly. The wall assembly with a stud-spacing of 610 mm failed at 74 minutes, while the one with a spacing of 406 mm failed at 59 minutes. Aside from the stud spacing, the two
assemblies were of similar configuration, and were loaded with corresponding specified loads. The higher fire resistance at the 610-mm spacing could be attributed to factors such as load redistribution to the two end studs that occur during the later stage of fire exposure.
The type of insulation also has a major influence, as illustrated in Figure 3. The uninsulated wall assembly provided the highest fire resistance, at 77 minutes. For the insulated assemblies, the highest fire resistance was provided by the cellulose fibre assembly at 71 minutes, followed by rock fibre at 59 minutes and glass fibre at 56 minutes. All four single-row stud walls, with two layers of gypsum board protection on each side, were of similar configuration except for the type of insulation. These results suggest that maximum fire
resistance in a steel stud wall assembly can be obtained with no insulation in the cavity.
The following additional factors were found to have an influence on the fire resistance of gypsum board-protected, steel stud wall
assemblies:
• Number of stud rows (double-stud walls have higher fire resistance)
• Number of gypsum board layers (two layers provide higher fire resistance)
• Replacing one gypsum board layer with an OSB shear membrane decreases fire resistance
• Installation of resilient channels for enhancing acoustical performance decreases fire resistance.
Impact on the Industry
As a result of this project and the parallel acoustics tests, a proposal for updating the fire- and sound-resistance ratings of wall assemblies in Part 9 of the NBC is being prepared by IRC together with its
industry partners. The number of listed steel stud wall assemblies is likely to be increased in the next issue of the code. This information will assist builders and regulators to provide suitable wall assemblies, particularly for multi-family dwellings.
____________________________ Notes:
IRC’s consortium partners were the Canadian Home Builders Association, the Canadian Sheet Steel Building Institute, the
Canadian Steel Construction Council, the Canadian Wood Council, the Cellulose Insulation Manufacturers Association of Canada,
Forintek Canada, Gypsum Manufacturers of Canada, Owens Corning Canada, and Roxul Inc.
It should be noted that the fire resistance of wall assemblies is dependent on a number of other factors such as fastener spacing, quality of gypsum board (manufacturer) and load level. Detailed information on these specifications, as well as details on the
assemblies tested and all the major results, including temperatures and deflections, are given in IRC/NRC Internal reports available from IRC.
_______________________________
Dr. V.K.R. Kodur is a research officer in the Fire Risk Management Program at the National Research Council’s Institute for Research in
Construction. Dr. M.A. Sultan is Manager of the Fire Resistant Construction sub-program.
5
Fire Resistance (min)
77 min
56 min
Figure 3. Effect of Insulation Type on the Fire Resistance
of Loadbearing Steel Stud (single row) Wall Assemblies 59 min
No Glass Fiber Rock Fibre Cellulose Insulation Insulation Insulation Insulation F37 F27 F38 F31 71 min Fir e R e sistanc e ( m in) 7 4 m in 5 9 m in F ig u re 2 . E ffe c t o f S tu d S p a c in g o n th e F ire R e s is ta n c e o f L o a d b e a rin g S te e l S tu d W a ll A s s e m b lie s 6 0 0 m m S p a c in g 4 0 0 m m S p a c in g (lo a d = 5 2 .4 K N ) (lo a d = 7 3 .3 K N ) F 2 8 F 3 8
Figure 1. A gypsum board protected steel stud wall assembly after testing in IRC’s propane-fired vertical furnace
