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TREATED WOOD PRODUCTS
TECHNICAL {VOTE
I FOR ADDITIONAL INFORMATION: www.Frtwxom or 1.800.TEC.WOOD (832,9663)
SPECIFICATIONS
PyroGuardTM Interior Fire -Retardant -Treated Wood
PART 1 - General Product Information
A. Lumber, plywood, and Engineered Wood Products (EWP) bearing the PyroGuardTM mark
has a flame spread rating of 25 or less (Class A) when tested in accordance with ASTM E84,
"Standard Test Method for Surface Burning Characteristics of Building Materials." PyroGuard''
fire -retardant -treated wood shows no evidence of significant progressive combustion when the
test is extended for an additional 20-minute period. In addition, the flame front does not
progress more than 101/2feet beyond the centerline of the burners at any time during the test.
The flame spread and smoke developed index for each species and product are classified by
Underwriters Laboratories Inc. (UL).
B. PyroGuard TI fire -retardant -treated wood is manufactured under the independent third -party
inspection of Underwriters Laboratories Inc. (UL) Follow -Up Service and each piece shall bear
the UL classified mark indicating the extended 30 minute ASTM E84 test.
C. PyroGuard"m shall be kiln dried after treatment (KDAT). The kiln drying process is monitored
by Underwriters Laboratories, Inc. (UL) and the UL mark shall appear on the label.
D. PyroGuard'"'shall be produced in accordance with UL Evaluation Report ER7002-01 (UL
ER7002-01), latest version.
E. PyroGuard"" meets the performance requirements of AWPA U1, Commodity Specification H
for Use Category UCFA and AWPA C20/C27 (Type A, HT).
F. PyroGuard'M is listed on the Department of Defense (DoD) Qualified Products List (QPL)
and meets the requirements of MIL-L-19140E as a Type 1 fire -retardant treatment for lumber
and plywood.
PART 2 - Fire -Retardant Treatment
A. Treatment shall be PyroGuard' manufactured by Hoover Treated Wood Products, Inc.
B. PyroGuardTM is an interior "Type A" fire -retardant with individual surface burning
characteristics for the species and products listed under UL Certifications.
C. Structural performance of PyroGuardTM fire -retardant -treated wood has been tested in
accordance with ASTM D5664 for lumber and ASTM D5516 for plywood. Evaluation of plywood
data is in accordance with ASTM D6305. Evaluation of lumber data is in accordance with ASTM
D6841. The resulting design value and span rating adjustments are published in UL ER7002-01,
which includes evaluation of high temperature (HT) strength testing for roof applications.
DISCLAIMER OF LIABILITY FOR RELIANCE ON INFORMATION PROVIDED BY HOOVER TREATED WOOD PRODUCTS, INC.; The information contained
herein is true and accurate to the best of our knowledge, but is provided without warranty or guarantee. Since the conditions of use are beyond our con-
trol, Hoover Treated Wood Products, Inc. ("Hoover"), disclaims all liability and assumes no legal responsibility for damages resulting from use of or reliance
upon the information contained herein. 02-2019
D. PyroGuardTM fire -retardant -treated wood is kiln dried after treatment (KDAT) to maximum
moisture content of 19% for lumber and 15% for plywood.
E. PyroGuardTM does not contain VOC's, urea formaldehyde or formaldehyde, halogens,
sulfates, chlorides, or ammonium phosphate.
F. Plywood treated with PyroGuardTM shall be manufactured under US Product Standards -
PS 1 or PS 2. Panels shall have a minimum bond durability of Exposure 1.
G. Grade marked lumber treated with PyroGuardTM shall be in accordance with PS 20.
PART 3 - Execution
A. PyroGuardTM fire -retardant -treated wood used in structural applications shall be installed in
accordance with the conditions and limitations listed in UL ER7002-01.
B. PyroGuardTMfire-retardant-treated wood shall be installed in compliance with the
requirements of the applicable building codes and product recommendations.
C. PyroGuardTM shall not be installed in areas where, in service, it is exposed to precipitation,
direct wetting, or condensation.
D. As with untreated wood, avoid exposure to precipitation during shipping, storage or
installation. Apply a water resistive barrier or underlayment over dry sheathing as soon as
practical to avoid precipitation on the panel. Panels that get wet should be allowed to dry before
covering, or be replaced.
DISCLAIMER OF LIABILITY FOR RELIANCE ON INFORMATION PROVIDED BY HOOVER TREATED WOOD PRODUCTS, INC.: The information contained
herein is true and accurate to the best of our knowledge, but is provided without warranty or guarantee. Since the conditions of use are beyond our con-
trol, Hoover Treated Wood Products, Inc. ("Hoover"), disclaims all liability and assumes no legal responsibility for damages resulting from use of or reliance
upon the information contained herein, 02-2019
Hoover
TM
TREATED WOOD PRODUCTS
TECHNICAL NOTE
I FOR ADDITIONAL INFORMATION: www.frtw.com or 1.800.TEC.WOOD (832.9663) 1
Fire -Retardant -Treated Wood Framed (Nall Assemblies
GENERAL INFORMATION
Fire-resistant construction assemblies (walls, floors, roofs) and elements (beams, columns), that
perform satisfactorily in standard fire resistance tests, are documented in building codes, standards,
test reports and directories of testing laboratories. Over the years, a considerable amount of
accumulated test data allowed the standardization of many fire-resistant designs involving generic
(non-proprietary) materials, such as wood, steel, concrete, masonry, clay tile, "Type X" gypsum
wallboard, and various plasters. These generalized designs and methods are documented in the
International Building Code, (IBC)' sections 720 and 721 with detailed explanatory figures, tables,
formulas, and charts. Fire resistant designs that incorporate proprietary materials pertaining to specific
manufacturers and/or patented are documented by test laboratories in test reports and directories of
test laboratories and trade associations. The major sources of documented construction designs rated
for fire resistance are described below.
UL DIRECTORY
Underwriters Laboratories Inc. (UL) conducts tests of various building components and fire
protection materials. The assemblies are tested under recognized testing procedures, including ASTM
Ell92 and ANSI/UL 2633, which are essentially the same. When the assembly complies with the
acceptance criteria of the fire test standard, a detailed report is provided including its description and
performance in the test, pertinent details, and specifications of materials used. A summary of the
important features is produced and given a UL designation. The assembly details are shown in the UL
Fire Resistance Directory, Volume 1 and their Online Certifications.
Volume 14 of the UL directory contains hourly fire resistance ratings for beams, floors, roofs,
columns, walls and partitions. Assemblies designated with a U3XX are wood framed wall assemblies.
These assemblies list untreated wood. However, UL makes the statement in their "General Information
for Fire Resistance Ratings" that, "Wood stud walls may contain fire -retardant -treated studs as well
as untreated wood studs. The use of fire -retardant -treated plywood (wood structural panels) may
be used in Designs that contain use of untreated plywood when all other specified attributes are
equivalent to the wood structural panel used in the Design." Using fire -retardant -treated wood in
these assemblies allows wood -framed wall systems where noncombustible materials are typically
required in Type I, II, III, and IV Construction.
TRADE ASSOCIATIONS
To facilitate the design process, numerous associations publish wall design configurations
meeting various fire criteria. Examples of these publications are Fire Rated Wood Floor and Wall
Assemblies (DCA-3)5 published by the American Wood Council, Fire Rated Systems
Design/Construction Guide (W305)6 published by APA-The Engineered Wood Association, and Fire
Resistance Design Manual (GA-600)' published by the Gypsum Association (see Appendix).
BUILDING CODE
The International Building Code (IBC)' requires that exterior walls conform to the required fire -
resistance ratings of Tables 601 and 602. Exterior bearing walls must comply with the more restrictive
requirements of both tables, whereas nonbearing exterior walls need only comply with Table 602.
The following are the code sections in the International Building Code for Fire -Retardant -Treated Wood
(FRTW) exterior walls.
EXTERIOR WALL USES FOR FRTW
IBC 2006
Type I and II Exterior nonbearing walls with 0 fire resistance or NC materials
required
603.1 #1.2
Exterior bearing and nonbearing walls in joisted masonry (Type III) construction.
602.3
Exterior bearing and nonbearing walls in heavy timber (Type IV) construction.
602.4
Fire -rated assemblies are required for the exterior bearing walls in Type III and Type IV construction.
The fire -resistance rating for bearing walls in Type III is two hours. For nonbearing walls with less than
30 feet fire separation distance the requirement is one hour; over 30 feet, no fire rating is required.
When the fire separation distance is greater than five feet the rating is from the interior side only
(Section 704.5); when 5 feet or closer, the rating must be from both the interior and exterior side.
To qualify under ASTM E119 an assembly must maintain structural stability, limit transmission of
heat, and limit transmission of hot gases. Failure to do any one of the three will result in the assembly
not passing the test. All three are important for interior fire rated assemblies. For exterior walls the
building code recognizes the distance between walls can influence how a fire can spread from building
to building and has modified the acceptance criteria. The exception in Section 703.2 states, in part:
"...compliance with the ASTM E 119 criteria for unexposed surface temperature rise and
ignition of cotton waste due to passage of flame or gases is required only for a period of
time corresponding to the required fire -resistance rating of an exterior nonbearing wall
with the same fire separation distance...."
For a bearing wall in Type III construction with a fire separation distance of more than 30 feet
the code is concerned with only structural stability; the limit on transmission of heat and hot gases is
not considered.
This provides a designer with much latitude in materials for use on exterior side of the wall. In Type III
construction wood used in the exterior wall must be fire -retardant treated.
EXAMPLES OF TWO HOUR FIRE RATED BEARING WALL ASSEMBLIES WITH
FIRE SEPARATION DISTANCE GREATER THAT 5 FEET
The modified assemblies shown in this section are based on UL 301 and UL 371. The original
assemblies, as tested, have fire protection from both sides. As permitted by the code, the modified
assemblies have the fire protection from the inside only.
U301 non -fire side modified
Weather Resistant Membrane
15132" Min. PYRO-GUARDt Treated Plywood
Jn,
518" Type X Gypsum Board
.. �x6 PYRO-GUARD® Treated Wood Studs @ 16" O.0
Note: See GA File No. WP 8416 for construction details for fire side.
side Follow manufacturer's recommendations for exterior membranes
U371 non -fire side modified
Various Exterior Finishes (Stucco, Brick Veneer, Cementitious Backer Units)
15/32" Min. PYRO-GUARD® Treated Plywood
5/8" Type X Gypsum Wallboard
2x4 OR 2x6 PYRO-GUARD a Treated Wood Studs @ 16" O.0
Note: See GA File No. WP 8417 for construction details for fire
Follow manufacturer's recommendations for exterior membranes
EXAMPLES OF TWO HOUR FIRE RATED BEARING WALL ASSEMBLIES WITH LESS THAN 5 FEET
FIRE SEPARATION DISTANCE
For illustration purposes, three UL assemblies are shown; U301, U302, and U371. An additional
assembly (15-1.6) which can be found in IBC Table 720.1(2) is also shown. Ratings for these two-hour
assemblies are from both sides. Figure 1 is a modified version of UL Design U301. This assembly has
been modified by adding PyroGuard" plywood to the exterior side of the wall. Section 703.3 of the IBC
allows modification of an assembly when the modification does not adversely affect the rating. The
modification is in accordance with the ten rules for fire endurance developed by T,Z, Harmathy. The ten
rules establish the impact of modifying an assembly and Rule #2 applies in this case, "The fire
endurance of a construction does not decrease with the addition of further layers," According to Rule #2,
PyroGuard" plywood can be added to any assembly to provide additional lateral load resistance to the
assembly. By adding a weather resistant membrane to UL U301, the gypsum board can also be
protected from exterior exposure and again Rule #2 applies.
Figure 1 - UL Design U301, Modified
Weather Resistant Membrane
5/8" Type X Gypsum Board
15/32" PYRO-GUARD® Treated Plywood
5/8" Type X Gypsum Board
2x4 PYRO-GUARD® Treated Wood Studs i@ 16" O.0
Note; See GA File No. WP 8416 for construction details.
The PyroGuard"" plywood can be placed against the studs or on the outside of the gypsum wallboard
Figure 2 is UL Design U302 which utilizes brick veneer for the exterior finish and provides the
required fire resistance to both sides of the wall. When resistance to lateral loads is required,
PyroGuard" treated plywood can be added to the exterior side without adversely affecting the fire
resistance of the assembly.
Clay Face Brick
Figure 2 - UL Design U3
/-_--..__L_r %0.!_11 Ties
prior Gypsum Sheathing
5/8" Type X Gypsum Wallboard
--- 2x4 PYRO-GUARD® Treated Wood Studs @ 16" O.0
Note: See GA File No. WP 8410 for construction details,
Local authority may permit substitution of the treated PyroGuard- plywood for the gypsum sheathing when fire
resistance is needed only from the interior.
Figure 3 demonstrates UL Design U371 which is similar to UL Design U302 in that it allows brick
veneer or stucco as the exterior membrane. This assembly shows the use of a wood sheathing
material for resisting lateral loads and unlike U302, which requires two layers, because the exterior
membranes are limited, this assembly requires only one layer of gypsum sheathing.
Figure 3 - UL Design U371
Various Exterior Finishes (Stucco, Brick Veneer, Cementitious Backer Units)
15/32" PYRO-GUARD® Treated Plywood
5/8" Exterior Gypsum Sheathing
A'er As'�X —f A X
5/8" Type X Gypsum Wallboard
2x4 PYRO-GUARD® Treated Wood Studs @ 16" O.0
Note: See GA File No. WP 8417 for construction details.
PyroGuard—treated plywood maybe installed over or under the gypsum sheathing.
Figure 4 illustrates a design from Table 720.1(2) of the IBC.
Figure 4 - IBC Design 720.1(2) 15-1.6
2 Coats Cement Plaster
Self Furred Exterior Lath Applied Over Building Paper
r/R" Tx/non X rvn-iim Sheathing
)® Treated Plywood, 3/8" min.
5/8" Type X Gypsum Wallboard
2x6 PYRO-GUARD" Treated Wood Studs c@ 16" O.0
Note: See GA File No. WP 8420 for construction details.
PyroGuard- treated plywood maybe installed over or under the gypsum sheathing
EXAMPLES OF ONE -HOUR FIRE RATED ASSEMBLIES
Depending on the fire separation distance the fire -resistance rating for the nonbearing walls can
be either one hour or none. There are many assemblies available in several documents. The
Component Added Method (CAM) in Section 721.6 of the IBC also provides a useful method to
calculate the fire resistance of wood framed assemblies. Two assemblies are provided. Figure 5 is for
a wall with fire resistance on both sides and Figure 6 is for fire resistance from the interior only. The
code requires the wall to be rated from both sides when the fire separation distance is five feet or less.
The two assemblies shown in the following section can be either bearing or nonbearing.
Figure 5 - Fire Separation Distance 5'-0" or less
A Inge.. CIOge T...—_ v /+..__..._ ��--`hing
gated Plywood, 3/8" min.
Note: 15/32" is recommended
5/8" Type X Gypsum Wallboard
1 1 1 ..,-.� Vlll %L.J 1 1 C.QLC.0 Wood Studs @ 16" O.0
Note: Insulation is optional
Additional membranes maybe installed over the PyroGuard-treated plywood; e.g., wood or other material siding, brick,
stucco, plaster.
Figure 6 - Fire Separation Distance > 5'-0"
PYRO-GUARD® Treated Plywood, 3/8" min.
Note: 15/32" is recommended
Fire Side _
5/8" Type X Gypsum Wallboard
PYRO-GUARD® Treated Wood Studs @ 16" O.0
Note: Insulation is optional
Additional membranes may be installed over the PyroGuard—treated plywood; e.g., wood or other material siding, brick,
stucco, plaster.
Gypsum sheathing maybe installed over or under the Pyro-Guard treated plywood.
REFERENCES
[1] International Code Council, Inc. (ICC) (2006), International Building Code, 2006, Falls Church, VA.
[2] American Society for Testing and Materials (ASTM) (2007), Standard Test Methods for Fire
Tests of Building Construction and Materials, Specification No. E119-07, West Conshohocken, PA.
[3] Underwriters Laboratories Inc. (UL) (2003), Fire Tests of Building Construction and Materials,
Thirteenth Edition, Standard No. UL 263, Northbrook, IL.
[4] Underwriters Laboratories Inc. (UL) (2003), Fire Resistance Directory, 2003, Vol.1, Northbrook, IL.
[5] American Wood Council (AWC) (2002), Fire Rated Wood Floor and Wall Assemblies
(DCA-3), Washington, DC.
[6] APA-The Engineered Wood Association (APA) (2005), Fire Rated Systems
Design/Construction Guide (W305), Tacoma, WA.
[7] Gypsum Association (GA) (2009), Fire Resistance Design Manual (GA-600-2009), Hyattsville, MD,
By Joe Holland and Dave Bueche, 08-08-11
Appendix A — Extracts from GA-600-2009 Fire Resistance Design Manual
EXTERIOR WALLS
GA FILE NO. WP 8410
GENERIC
GYPSUM WALLBOARD, WOOD STUDS, GYPSUM SHEATHING,
CLAY BRICK
EXTERIOR SIDE: Base layer 1/2" gypsum sheathing applied parallel or at right angles to 2
x 4 wood studs 16" o.c. with 13/4" galvanized roofing nails, 0.125" shank, T116' heads, 6"
o.c. Face layer 2" x 4" x 8" clay brick with 1" air space between brick and exterior
sheathing. No. 20 gage galvanized wire ties attached to each stud with 8d coated nails,
23/8" long, 0.113" shank, 9132" head, at every 6th course of bricks.
INTERIOR SIDE: Base layer 5/a" type X gypsum wallboard or gypsum veneer base applied
parallel or at right angles to studs with 6d coated nails, 17/8" long, 0.0915" shank, 1/4"
heads, 8" o.c. Face layer 5/8" type X gypsum wallboard or gypsum veneer base applied
parallel to or at right angles to studs with 8d coated nails, 23/8" long, 0.113" shank, 9/32"
heads, 8" o.c. (LOAD -BEARING)
GA FILE NO. WP 8415 1 1 GENERIC
GYPSUM SHEATHING, GYPSUM WALLBOARD, WOOD STUDS
EXTERIOR SIDE: Base layer 518" type X gypsum sheathing applied parallel or at right
angles to 2 x 4 wood studs 24" o.c. with 6d coated nails, 17/a" long, 0.085' shank, 1/4"
heads, 24" o.c. Face layer 5/8" type X gypsum sheathing applied parallel or at right
angles to studs with 8d coated nails, 23/8" long, 0.100" shank, 1/4" heads, 8" o.c. Exterior
cladding attached through sheathing to studs.
INTERIOR SIDE: Base layer 5/8" type X gypsum wallboard or gypsum veneer base applied
paralle or at right angles to studs with 6d coated nails, 17/a" long, 0.085' shank, 1/4"
heads, 24" o.c. Face layer 5/8" type X gypsum wallboard or gypsum veneer base applied
parallel or at right angles to studs with 8d coated nails, 23/8" long, 0.100" shank, 1/4"
heads, 8" o.c.
Joints staggered 24" each layer and side. (LOAD -BEARING)
GA FILE NO. WP 8416 1 1 PROPRIETARY`'
GYPSUM WALLBOARD, GLASS MAT GYPSUM SUBSTRATE,
WOOD STUDS
EXTERIOR SIDE: Base layer 5/s" proprietary type X glass mat gypsum substrate
(sheathing) applied parallel or at right angles to 2 x 4 wood studs 16" o.c. with 1718",
0.0915" shank, 1/4" head, galvanized roofing nails 6" o.c. Face layer 5/a" proprietary type
X glass mat gypsum substrate (sheathing) applied parallel or at right angles to studs to
with 23/8", 0.113" shank, 9/32" head, galvanized roofing nails 8" o.c. Exterior cladding to
be attached through glass mat gypsum panel to studs.
INTERIOR SIDE: Base layer 5/8" proprietary type X gypsum board applied parallel or at
right angles to studs with 17/8", 0.0915" shank, 1/4" head nails 6" o.c. Face layer 5/8"
proprietary type X gypsum board applied parallel or at right angles to studs with 23/8",
0.113" shank, 9/32" head nails 8" o.c.
Joints staggered 16" each layer and side. (LOAD -BEARING)
PROPRIETARY GYPSUM PANEL PRODUCTS
CertainTeed Gypsum Inc.
- 5/8" ProRoc® Type X Gypsum Panels
- 5/a" GlasRoa Sheathing Type X
Gypsum Panels
CertainTeed Gypsum Canada Inc.
- 518" ProRocO Type X Gypsum Panels
National Gypsum Company
- 5/8" e2XPO FIRE -SHIELD@
Gypsum Sheathing
- 5/8" Gold Bond@ Brand FIRE -SHIELD@
Gypsum Board
Temple-Inland
- 5/a" GreenGlass Type X
- 5/8" Type X
2 HOUR
FIRE
Thickness: 101/8"
Fire Test: UL R1505-1, 2, 4-22-65,
UL Design U302;
ULC Design U302
2 HOUR
FIRE
T
Thickness:
Fire Test:
2 HOUR
FIRE
61/a" without exterior cladding
See WP 4135
(FM WP 360, 9-27-74)
Thickness: 61/8"
Approx. Weight: 12 psf
Fire Test: Based on UL R3660IR15187,
2-4-02;
UL R6937, 08NK02787,
9-19-08;
UL Design U301
Appendix A — Extracts from GA-600-2009 Fire Resistance
Design Manual
(continued)
EXTERIOR WALLS
GA FILE NO. WP 8417 PROPRIETARY*
HOUR
GYPSUM WALLBOARD, WOOD STUDS, GYPSUM SHEATHING
L2 FIRE
STUCCO NETTINGy CEMENT STUCCO
EXTERIOR SIDE: Base layer 51a" proprietary type X gypsum sheathing applied parallel or
at right angles to 2 x 4 wood studs 16" o.c, with 131a", 0.125"
shank, t1is" head galvanized
roofing nails 8- o.c. or 2" Type S drywall screws 8" o.c, Pre -furred wire stucco netting
applied over gypsum shealhing with 1114" x 1" steel staples 7" o.c. Portland Dement
stucco, 314", applied over stucco netting.
i
INTERIOR SIDE: Base layer Va" proprietary type X gypsum wallboard or gypsum veneer
base applied parallel or at right angles to studs with 1114" Type
S drywall screws 12" o.c.
Face layer Sla" proprietary lype X gypsum wallboard or gypsum veneer base applied
parallel or at right angles to studs with 2" Type
Thickness: 61/4"
S drywall screws 12" o.c,
Approx. Weight: 17 psf
Joints staggered 16" each layer and side. (LOAD -BEARING)
Fire Test: UL R3501, 03NK2475,
PROPRIETARY GYPSUM BOARD
National Gypsum Company 5/8"
5-21-03,
UL Design U371
- Gold Bond(@ Brand FIRE-SHIELDO
Gypsum Boa, d
- 5/s" Gold Bond@ Brand FIRE-SHIELDv>
Gypsum Sheathing
GA FILE NO. WP 8420 GENERIC
2 HOUR
WOOD STUDS, CEMENT STUCCO, WIRE MESH,
FIRE
GYPSUM WALLBOARD__A
EXTERIQR SIl]E: Base layer Sle" type X applied parallel to 2 x S fire
retardant treated woad studs iS" o.c, with 6d
FIRE SIDE
coated nails, J$" long, 0.0915" shank, ila"
heads, 12" o.c. and covered with a single layer {re resistant protective weather retarder
'
paper stapled along each edge at 16" o.c. Galvanized self -furring wire mesh applied
over sheathing with 8d galvanized roofing
nails, 231C long, 0.113" shank, 91az" heads, 6"
o.c. Cement -stucco applied over wire mesh in two 1Iz' thick coats with bonding agent
applied between coats.
--
INTERIOR SIDE: Base layer 51s" type X Y yp gypsum wallboard or gypsum veneer base applied
parallel to studs with 6d coated nails, 1�Ja" tong, 0.0915" shank, 114" heads, 12" O.C. Face
layer 51s" type X gypsum wal{hoard or gypsum veneer base
Thickness: 85/8"
applied at right angles to
studs with 8d coated nails, 23/a" long, 0.113" shank, 'VW heads, 8" o,c, at edges and 12"
Fire Test: UC, 12-21-67
o.c. at intermediate studs. {LOAD -BEARING)
This Space Left Blank
Appendix B - Harmathy's 10 Rules of Fire Endurance
Rule I. The "thermal" fire endurance of a construction consisting of a number of parallel layers is greater
than the sum of the "thermal" fire endurance characteristics of the individual layers when exposed
separately to fire.
Rule 2. The fire endurance of a construction does not decrease with the addition of further layers.
Rule 3. The fire endurance of constructions containing continuous air gaps or cavities is greater than the
fire endurance of similar constructions of the same weight but containing no air gaps or cavities.
Rule 4. The farther an air gap or cavity is located from the exposed surface, the more beneficial its effect on
the fire endurance.
Rule 5. The fire endurance of an assembly cannot be increased by increasing the thickness of completely
enclosed air layer.
Rule 6. Layers of materials of low thermal conductivity are better utilized on the side of the construction
on which fire is more likely to happen.
Rule 7. The fire endurance of asymmetrical constructions depends on the direction of heat flow.
Rule B. The presence of moisture, if it does not result in explosive spalling, increases the fire endurance.
Rule 9. Load -supporting elements, such as beams, girders an assidthanher fire endurance when
they would when tested
subject to fire endurance tests as parts of floor, roof or ceiling assemblies
separately.
Rule 10. The load -supporting elements (beams, girders, joists, etc.) of a floor, roof or ceiling assembly can
be replaced by such other load -supporting elements which, when tested separately, yielded fire
endurance not less than that of the assembly.