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Frequent Asked Questions
National Gypsum Company
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
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
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
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
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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