FIRE ENDURANCE, SOUND
TRANSMISSION
| Figure 1 
Direct application of gypsum.
1-Hour-Rated, STC 35-39, FC 5410.
Wood Joists, Gypsum Wallboard: 1/2" type X gypsum
wallboard or veneer base applied at right angles to 2 x 10 wood joists 16" o.c. |
| Figure 2. 
Resilient channels and insulation.
1-Hour-Rated, STC 55-59, FC 5105.
Wood Joists, Gypsum Wallboard: 1/2" proprietary type X
gypsum wallboard or veneer base applied at right angles to resilient furring channels with
1" Type S drywall screws 12" o.c. Resilient channels applied 24" o.c. at
right angles to 2 x 10 wood joists 16" o.c. with 6d common nail. |
| Figure 3. 
Resilient channels between gypsum layers.
2-Hour-Rated, FC 5724.
Wood Floor, Wood Joists, Gypsum Wallboard: Base layer
5/8" proprietary type X gypsum wallboard or veneer base applied at right angles to 2
x 10 wood joists 16" o.c. Face layer 5/8" proprietary type X gypsum wallboard or
veneer base applied at right angles to resilient furring channels with 1" Type S
drywall screws 12" o.c. Resilient furring channel spaced 24" o.c. and nailed at
right angles to joists and through base layer. |
| Figure 4. 
Direct application of two layers of gypsum.
1-Hour-Rated, FC 5512.
Gypsum Board, Parallel Chord Wood Trusses: Ceiling - Two
layers of 1/2" type X gypsum wallboard or veneer base applied perpendicular to
trusses. Base layer end joints staggered 24" and all face layer joints offset
24" from the joints of the base layer. Trusses - chord and web members are fabricated
from 2 x 4 lumber with 20 gauge steel connector plates that have a minimum tooth length of
5/16". Trusses are spaced a maximum of 24" o.c. Furring channels 24" o.c.
secured with steel wire 48" o.c. perpendicular to parallel chord wood trusses
24" o.c. with a minimum depth of 12". |
| Figure 5. 
Single gypsum layer on resilient channels.
1-Hour-Rated, FC 5515.
Wood Trusses, Gypsum Wallboard: 5/8" proprietary type
X gypsum wallboard or veneer base applied at right angles to steel furring channel with
1" Type S drywall screws 12" o.c. Furring channels 24" o.c. secured with
steel wire 48" o.c. perpendicular to parallel chord wood trusses 24" o.c. with a
minimum depth of 12". |
Dimension lumber joists and rafters have a long
history of solid fire endurance performance. The first fire endurance assemblies developed
for wood frame structures were performed using dimension lumber structural members.
Further evidence of this exists in the codes where
calculating fire endurance assemblies is allowed. Times are assigned for the contribution
of wood-frame construction in fire assembly calculation sections (i.e. 709.6.2B of the
Standard Building Code). Wood floor and ceiling joists 16" on center, have a time of
10 minutes assigned to them. For additional information on this, see Component Additive
Method (CAM) for Calculating and Demonstrating Assembly Fire Endurance, Design for Code
Acceptance No. 4, from the American Forest & Paper Association. Fire endurance
assemblies have also been developed for metal plate connected trusses.
Properly designing a building for fire
safety means faithfully executing building code regulations. This means
breaking up a building into fire-resistant compartments. With compartments
and an efficient protection system in place, fires can be localized
and suppressed easily. Top prevent fire from spreading from one compartment
to the next, the codes require finished assemblies be built to withstand
full fire exposure without major damage and, at the same time, act as
barriers to heat transfer.
Standard fire tests measure the fire endurance performance
of a variety of structural assemblies and boundary conditions that make up compartments.
In North America, ASTM Standard E 119 sets forth the conditions of the test and the
interpretation of the results. Test results are measured in terms of the assembly's
ability to withstand a severe fire for a period of time. Performance times are measured in
hours: 1-hour rated; 2-hour rated; etc. The codes reference these hourly requirements for
various building construction types and occupancies.
The two major source documents for dimension lumber and
truss fire-endurance assemblies are the Fire Resistance Design manual published by the
Gypsum Association, and the Fire Resistance Directory published by the Underwriters
Laboratories, Inc. (UL). The assemblies in these documents range in performance from
1-hour to 2-hours, providing flexibility for any project need.
The most common dimension lumber and truss assembly types
are detailed in Figures 1-5, and are excerpted from the Gypsum Association's manual.
Included are assemblies having direct gypsum application, resilient channels and
insulation, and a 2-hour assembly. For suspended ceiling assemblies, see the UL directory.
 |
| (1) Dock & Harbor Authority, London,
England, "What About Fire?" , American Institute of Timber Construction, 1972,
p.3. |
Wood has out-performed non-combustible materials in direct
comparison fire tests. As illustrated above, a 2x4 timber tie maintained more of its
original strength under higher temperatures and for a longer period of time than did
aluminum alloy or mild steel. This is because of wood's unique charring properties, which
actually protect it from fire. As such, wood can be an excellent performer under fire
conditions, contrary to prevalent concerns over its combustibility. |
