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Understanding the UL Directory:
Fire-Resistant Assemblies
Creating Code-Compliant Designs
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Advertising supplement provided by
National Gypsum Company

Frequent Asked Questions

What does it mean to say that a particular wall or ceiling system has achieved a 1-hour fire rating?

The term "1 hour fire-rated system" is generally used to refer to a system that has been shown, in a carefully controlled laboratory test, or by rigorous technical analysis, to be capable of limiting the transmission of high temperatures to a specified maximum, and to meet other requirements, for at least 60 minutes. (ASTM E119

When constructing a fire-rated wallboard partition, must the exact stud size specified in the tested design be utilized?

No. Specified wood or steel stud sizes are minimum unless otherwise stated in the design. Wood stud walls may contain fire retardant treated studs as well as untreated wood studs. The hourly ratings for steel stud partitions are maintained when the steel studs are of a heavier gauge and/or larger dimensions than specified in a design.

My fire rated design was tested with nails. Can I fasten the wallboard with screws as an alternate to nails?

Yes, screws can be used as an alternate to nails in wallboard designs. Diameter of screw head, length of the screw and shank must be the same size or larger than nail size specified in the design. Note: Spacing of screws must be the same as the spacing of the nails specified in the fire rated design.

Can I add glass fiber insulation to a fire rated partition design when it is not specified as a component?

Yes, glass fiber insulation of a thickness not exceeding the depth of the stud is OK to add to the stud cavity.

Yes, for 1-hour rated G500, L500, and P500 series floor-ceiling assemblies, fiberglass insulation may be added to the plenum or joist space above the gypsum wallboard provided an additional layer of gypsum wallboard is added to the assembly.

What is the difference between "regular" and "Type X" gypsum wallboard?

ASTM C 36 designates two types of gypsum wallboard, regular and type X. Type X wallboard, which is typically required to achieve fire resistance ratings, is formulated by adding noncombustible fibers to the gypsum. These fibers help maintain the integrity of the core as shrinkage occurs, providing greater resistance to heat transfer during fire exposure. To receive the "Type X" designation under ASTM c 36, a gypsum wallboard product must be shown to achieve not less than a one hour fire resistance rating for 5/8" board or a 3/4 hour fire resistance rating for 1/2" board applied in a single layer, nailed on each face of load-bearing wood framing members, when tested in accordance with the requirements of ASTM E119 Methods of Fire Test of Building Constructions and materials.

What is the fire rating for 5/8" Type X Wallboard?

5/8" Type X Wallboard has no fire rating. Fire ratings are assigned to a complete construction assembly that may include 5/8" Type X Wallboard as a component.

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