International Building Code Section 721


International Building Code 721.1

General. The provisions of this section contain procedures
by which the fire resistance of specific materials or combinations
of materials is established by calculations. These
procedures apply only to the information contained in this section
and shall not be otherwise used. The calculated fire resistance
of concrete, concrete masonry, and clay masonry
assemblies shall be permitted in accordance with ACI
216.1/TMS 0216. The calculated fire resistance of steel assemblies
shall be permitted in accordance with Chapter 5 of ASCE
29.

Definitions. The following words and terms shall,
for the purposes of this chapter and as used elsewhere in this
code, have the meanings shown herein.
CERAMIC FIBER BLANKET. A mineral wool insulation
material made of alumina-silica fibers and weighing 4
to 10 pounds per cubic foot (pcf) (64 to 160 kg/m3).
CONCRETE, CARBONATE AGGREGATE. Concrete
made with aggregates consisting mainly of calcium or magnesium
carbonate, such as limestone or dolomite, and containing
40 percent or less quartz, chert, or flint.
CONCRETE, CELLULAR. A lightweight insulating
concrete made by mixing a preformed foam with portland
cement slurry and having a dry unit weight of approximately
30 pcf (480 kg/m3).
CONCRETE, LIGHTWEIGHT AGGREGATE. Concrete
made with aggregates of expanded clay, shale, slag or
slate or sintered fly ash or any natural lightweight aggregate
meeting ASTM C 330 and possessing equivalent fire-resistance
properties and weighing 85 to 115 pcf (1360 to 1840
kg/m3).
CONCRETE, PERLITE. A lightweight insulating concrete
having a dry unit weight of approximately 30 pcf (480
kg/m3) made with perlite concrete aggregate. Perlite aggregate
is produced from a volcanic rock which, when heated,
expands to form a glass-like material of cellular structure.
CONCRETE, SAND-LIGHTWEIGHT. Concrete made
with a combination of expanded clay, shale, slag, slate,
sintered fly ash, or any natural lightweight aggregate meeting
ASTM C 330 and possessing equivalent fire-resistance
properties and natural sand. Its unit weight is generally
between 105 and 120 pcf (1680 and 1920 kg/m3).
CONCRETE, SILICEOUS AGGREGATE. Concrete
made with normal-weight aggregates consisting mainly of
silica or compounds other than calcium or magnesium carbonate,
which contains more than 40-percent quartz, chert,
or flint.
CONCRETE, VERMICULITE.Alightweight insulating
concrete made with vermiculite concrete aggregate which is
laminated micaceous material produced by expanding the
ore at high temperatures. When added to a portland cement
slurry the resulting concrete has a dry unit weight of approximately
30 pcf (480 kg/m3).
GLASS FIBERBOARD. Fibrous glass roof insulation
consisting of inorganic glass fibers formed into rigid boards
using a binder. The board has a top surface faced with
asphalt and kraft reinforced with glass fiber.
136 2006 INTERNATIONAL BUILDING CODE
FIRE-RESISTANCE-RATED CONSTRUCTION

MINERAL BOARD. A rigid felted thermal insulation
board consisting of either felted mineral fiber or cellular
beads of expanded aggregate formed into flat rectangular
units.

International Building Code 721.1.1

Definitions. The following words and terms shall,
for the purposes of this chapter and as used elsewhere in this
code, have the meanings shown herein.
CERAMIC FIBER BLANKET. A mineral wool insulation
material made of alumina-silica fibers and weighing 4
to 10 pounds per cubic foot (pcf) (64 to 160 kg/m3).
CONCRETE, CARBONATE AGGREGATE. Concrete
made with aggregates consisting mainly of calcium or magnesium
carbonate, such as limestone or dolomite, and containing
40 percent or less quartz, chert, or flint.
CONCRETE, CELLULAR. A lightweight insulating
concrete made by mixing a preformed foam with portland
cement slurry and having a dry unit weight of approximately
30 pcf (480 kg/m3).
CONCRETE, LIGHTWEIGHT AGGREGATE. Concrete
made with aggregates of expanded clay, shale, slag or
slate or sintered fly ash or any natural lightweight aggregate
meeting ASTM C 330 and possessing equivalent fire-resistance
properties and weighing 85 to 115 pcf (1360 to 1840
kg/m3).
CONCRETE, PERLITE. A lightweight insulating concrete
having a dry unit weight of approximately 30 pcf (480
kg/m3) made with perlite concrete aggregate. Perlite aggregate
is produced from a volcanic rock which, when heated,
expands to form a glass-like material of cellular structure.
CONCRETE, SAND-LIGHTWEIGHT. Concrete made
with a combination of expanded clay, shale, slag, slate,
sintered fly ash, or any natural lightweight aggregate meeting
ASTM C 330 and possessing equivalent fire-resistance
properties and natural sand. Its unit weight is generally
between 105 and 120 pcf (1680 and 1920 kg/m3).
CONCRETE, SILICEOUS AGGREGATE. Concrete
made with normal-weight aggregates consisting mainly of
silica or compounds other than calcium or magnesium carbonate,
which contains more than 40-percent quartz, chert,
or flint.
CONCRETE, VERMICULITE.Alightweight insulating
concrete made with vermiculite concrete aggregate which is
laminated micaceous material produced by expanding the
ore at high temperatures. When added to a portland cement
slurry the resulting concrete has a dry unit weight of approximately
30 pcf (480 kg/m3).
GLASS FIBERBOARD. Fibrous glass roof insulation
consisting of inorganic glass fibers formed into rigid boards
using a binder. The board has a top surface faced with
asphalt and kraft reinforced with glass fiber.
136 2006 INTERNATIONAL BUILDING CODE
FIRE-RESISTANCE-RATED CONSTRUCTION

MINERAL BOARD. A rigid felted thermal insulation
board consisting of either felted mineral fiber or cellular
beads of expanded aggregate formed into flat rectangular
units.

International Building Code 721.2

Concrete assemblies. The provisions of this section
contain procedures by which the fire-resistance ratings of concrete
assemblies are established by calculations.

Concrete walls. Cast-in-place and precast concrete
walls shall comply with Section 721.2.1.1. Multiwythe concrete
walls shall comply with Section 721.2.1.2. Joints
between precast panels shall comply with Section
721.2.1.3. Concretewalls with gypsum wallboard or plaster
finish shall comply with Section 721.2.1.4.

Cast-in-place or precast walls. The minimum
equivalent thicknesses of cast-in-place or precast
concrete walls for fire-resistance ratings of 1 hour to 4
hours are shown in Table 721.2.1.1. For solid walls with
flat vertical surfaces, the equivalent thickness is the same
as the actual thickness. The values in Table 721.2.1.1
apply to plain, reinforced or prestressed concrete walls.

Hollow-core precast wall panels. For
hollow-core precast concretewall panels in which the
cores are of constant cross section throughout the
length, calculation of the equivalent thickness by
dividing the net cross-sectional area (the gross cross
section minus the area of the cores) of the panel by its
width shall be permitted.

Core spaces filled. Where all of the core
spaces of hollow-core wall panels are filled with
loose-fill material, such as expanded shale, clay, or
slag, or vermiculite or perlite, the fire-resistance rating
of the wall is the same as that of a solid wall of the
same concrete type and of the same overall thickness.

Tapered cross sections. The thickness of
panels with tapered cross sections shall be that determined
at a distance 2t or 6 inches (152 mm), whichever
is less, from the point of minimum thickness,
where t is the minimum thickness.

Ribbed or undulating surfaces. The
equivalent thickness of panels with ribbed or undulating
surfaces shall be determined by one of the
following expressions:
(Equation 7-3)
where:
s = Spacing of ribs or undulations.
t = Minimum thickness.
te = Equivalent thickness of the panel calculated as
the net cross-sectional area of the panel divided
by the width, in which the maximum thickness
used in the calculation shall not exceed 2t.

Multiwythe walls. For walls that consist of
two wythes of different types of concrete, the fire-resistance
ratings shall be permitted to be determined from
Figure 721.2.1.2.

Two or more wythes. The fire-resistance
rating forwall panels consisting of two or morewythes
shall be permitted to be determined by the formula:
(Equation 7-4)
where:
R = The fire endurance of the assembly, minutes.
R1, R2, and Rn = The fire endurances of the individual
wythes,minutes.Values ofRn
0.59 for use in Equation 7-4
are given in Table 721.2.1.2(1). Calculated fire-resistance
ratings are shown in Table 721.2.1.2(2).
2006 INTERNATIONAL BUILDING CODE 137
FIRE-RESISTANCE-RATED CONSTRUCTION
For SI: 1 inch = 25.4 mm.
FIGURE 721.2.1.2
FIRE-RESISTANCE RATINGS OF
TWO-WYTHE CONCRETE WALLS

Foam plastic insulation. The fire-resistance
ratings of precast concrete wall panels consisting
of a layer of foam plastic insulation sandwiched
between two wythes of concrete shall be permitted to
be determined by use of Equation 7-4. Foam plastic
insulation with a total thickness of less than 1 inch (25
mm) shall be disregarded. The Rn value for thickness
of foam plastic insulation of 1 inch (25 mm) or
greater, for use in the calculation, is 5 minutes; therefore
Rn
0.59 = 2.5.

Joints between precast wall panels. Joints
between precast concretewall panels which are not insulated
as required by this section shall be considered as
openings inwalls. Uninsulated joints shall be included in
determining the percentage of openings permitted by
Table 704.8. Where openings are not permitted or are
required by this code to be protected, the provisions of
this section shall be used to determine the amount of joint
insulation required. Insulated joints shall not be considered
openings for purposes of determining compliance
with the allowable percentage of openings in Table
704.8.

Ceramic fiber joint protection. Figure
721.2.1.3.1 shows thicknesses of ceramic fiber blankets
to be used to insulate joints between precast concretewall
panels for various panel thicknesses and for
joint widths of 3/8 inch (9.5 mm) and 1 inch (25 mm)
for fire-resistance ratings of 1 hour to 4 hours. For
joint widths between 3/8 inch (9.5 mm) and 1 inch (25
mm), the thickness of ceramic fiber blanket is allowed
to be determined by direct interpolation. Other tested
and labeled materials are acceptable in place of
ceramic fiber blankets.

Walls with gypsum wallboard or plaster finishes.
The fire-resistance rating of cast-in-place or precast
concrete walls with finishes of gypsum wallboard or
plaster applied to one or both sides shall be permitted to
be calculated in accordance with the provisions of this
section.

Nonfire-exposed side. Where the finish
of gypsum wallboard or plaster is applied to the side
of the wall not exposed to fire, the contribution of the
finish to the total fire-resistance rating shall be determined
as follows: The thickness of the finish shall
first be corrected by multiplying the actual thickness
of the finish by the applicable factor determined from
Table 721.2.1.4(1) based on the type of aggregate in
the concrete. The corrected thickness of finish shall
then be added to the actual or equivalent thickness of
concrete and fire-resistance rating of the concrete and
finish determined from Table 721.2.1.1, Figure
721.2.1.2 or Table 721.2.1.2(1).

Fire-exposed side. Where gypsum wallboard
or plaster is applied to the fire-exposed side of
the wall, the contribution of the finish to the total
fire-resistance rating shall be determined as follows:
The time assigned to the finish as established by Table
721.2.1.4(2) shall be added to the fire-resistance rating
determined from Table 721.2.1.1 or Figure 721.2.1.2,
or Table 721.2.1.2(1) for the concrete alone, or to the
rating determined in Section 721.2.1.4.1 for the concrete
and finish on the nonfire-exposed side.
138 2006 INTERNATIONAL BUILDING CODE
FIRE-RESISTANCE-RATED CONSTRUCTION

Nonsymmetrical assemblies. For a wall
having no finish on one side or different types or
thicknesses of finish on each side, the calculation procedures
of Sections 721.2.1.4.1 and 721.2.1.4.2 shall
be performed twice, assuming either side of the wall
to be the fire-exposed side. The fire-restance rating of
thewall shall not exceed the lower of the two values.
Exception: For an exterior wall with more than 5
feet (1524 mm) of horizontal separation, the fire
shall be assumed to occur on the interior side only.

Minimum concrete fire-resistance rating.
Where finishes applied to one or both sides of a
concrete wall contribute to the fire-resistance rating,
the concrete alone shall provide not less than one-half
of the total required fire-resistance rating. Additionally,
the contribution to the fire resistance of the finish
on the nonfire-exposed side of a load-bearingwall shall
not exceed one-half the contribution of the concrete
alone.

Concrete finishes. Finishes on concrete
walls that are assumed to contribute to the total
fire-resistance rating of thewall shall comply with the
installation requirements of Section 721.3.2.5.

Concrete floor and roof slabs. Reinforced and
prestressed floors and roofs shall comply with Section
721.2.2.1. Multicourse floors and roofs shall comply with
Sections 721.2.2.2 and 721.2.2.3, respectively.

Reinforced and prestressed floors and
roofs. The minimum thicknesses of reinforced and prestressed
concrete floor or roof slabs for fire-resistance
ratings of 1 hour to 4 hours are shown inTable 721.2.2.1.

Hollow-core prestressed slabs. For hollow-
core prestressed concrete slabs in which the cores
are of constant cross section throughout the length,
the equivalent thickness shall be permitted to be
obtained by dividing the net cross-sectional area of
the slab including grout in the joints, by its width.

Slabs with sloping soffits. The thickness
of slabs with sloping soffits (see Figure 721.2.2.1.2)
shall be determined at a distance 2t or 6 inches (152
mm), whichever is less, from the point of minimum
thickness, where t is the minimum thickness.

Slabs with ribbed soffits. The thickness
of slabs with ribbed or undulating soffits (see Figure
721.2.2.1.3) shall be determined by one of the following
expressions, whichever is applicable:
(Equation 7-5)
where:
s = Spacing of ribs or undulations.
t = Minimum thickness.
te = Equivalent thickness of the slab calculated as
the net area of the slab divided by the width, in
which the maximum thickness used in the calculation
shall not exceed 2t.

Multicourse floors. The fire-resistance ratings
of floors that consist of a base slab of concrete with a
topping (overlay) of a different type of concrete shall
comply with Figure 721.2.2.2.
140 2006 INTERNATIONAL BUILDING CODE
FIRE-RESISTANCE-RATED CONSTRUCTION
For SI: 1 inch = 25.4 mm.
FIGURE 721.2.2.1.3
SLABS WITH RIBBED OR UNDULATING SOFFITS
For SI: 1 inch = 25.4 mm.
FIGURE 721.2.2.1.2
DETERMINATION OF SLAB THICKNESS
FOR SLOPING SOFFITS

Multicourse roofs. The fire-resistance ratings
of roofs which consist of a base slab of concrete with a
topping (overlay) of an insulating concrete or with an
insulating board and built-up roofing shall comply with
Figures 721.2.2.3(1) and 721.2.2.3(2).

Heat transfer. For the transfer of heat,
three-ply built-up roofing contributes 10 minutes to
the fire-resistance rating. The fire-resistance rating
for concrete assemblies such as those shown in Figure
721.2.2.3(1) shall be increased by 10 minutes. This
increase is not applicable to those shown in Figure
721.2.2.3(2).

Joints in precast slabs. Joints between adjacent
precast concrete slabs need not be considered in calculating
the slab thickness provided that a concrete
topping at least 1 inch (25 mm) thick is used. Where no
concrete topping is used, joints must be grouted to a
depth of at least one-third the slab thickness at the joint,
but not less than 1 inch (25 mm), or the joints must be
made fire resistant by other approved methods.

Concrete cover over reinforcement. The minimumthickness
of concrete cover over reinforcement in concrete
slabs, reinforced beams and prestressed beams shall
comply with this section.

Slab cover. The minimum thickness of concrete
cover to the positive moment reinforcement shall
comply with Table 721.2.3(1) for reinforced concrete
and Table 721.2.3(2) for prestressed concrete. These
tables are applicable for solid or hollow-core one-way or
two-way slabs with flat undersurfaces. These tables are
applicable to slabs that are either cast in place or precast.
For precast prestressed concrete not covered elsewhere,
the procedures contained in PCI MNL 124 shall be
acceptable.

Reinforced beam cover. The minimum thickness
of concrete cover to the positive moment reinforcement
(bottom steel) for reinforced concrete beams is
shown in Table 721.2.3(3) for fire-resistance ratings of 1
hour to 4 hours.

Prestressed beam cover. The minimum thickness
of concrete cover to the positive moment
prestressing tendons (bottom steel) for restrained and
unrestrained prestressed concrete beams and stemmed
units shall comply with the values shown in Tables
721.2.3(4) and 721.2.3(5) for fire-resistance ratings of 1
hour to 4 hours. Values in Table 721.2.3(4) apply to
beams 8 inches (203 mm) or greater in width. Values in
Table 721.2.3(5) apply to beams or stems of any width,
provided the cross-section area is not less than 40 square
inches (25 806 mm2). In case of differences between the
values determined from Table 721.2.3(4) or 721.2.3(5),
it is permitted to use the smaller value. The concrete
cover shall be calculated in accordance with Section
721.2.3.3.1. The minimum concrete cover for
nonprestressed reinforcement in prestressed concrete
beams shall comply with Section 721.2.3.2.

Calculating concrete cover. The concrete
cover for an individual tendon is the minimum
thickness of concrete between the surface of the tendon
and the fire-exposed surface of the beam, except
that for ungrouped ducts, the assumed cover thickness
is the minimum thickness of concrete between
the surface of the duct and the fire-exposed surface
of the beam. For beams in which two or more tendons
are used, the cover is assumed to be the average
of the minimum cover of the individual tendons. For
corner tendons (tendons equal distance from the bottom
and side), the minimum cover used in the calculation
shall be one-half the actual value. For
stemmed members with two or more prestressing
tendons located along the vertical centerline of the
stem, the average cover shall be the distance from the
bottomof the member to the centroid of the tendons.
The actual cover for any individual tendon shall not
be less than one-half the smaller value shown in
Tables 721.2.3(4) and 721.2.3(5), or 1 inch (25 mm),
whichever is greater.
2006 INTERNATIONAL BUILDING CODE 141
FIRE-RESISTANCE-RATED CONSTRUCTION
For SI: 1 inch = 25.4 mm.
FIGURE 721.2.2.2
FIRE-RESISTANCE RATINGS FOR TWO-COURSE
CONCRETE FLOORS
142 2006 INTERNATIONAL BUILDING CODE
FIRE-RESISTANCE-RATED CONSTRUCTION

Concrete columns. Concrete columns shall comply
with this section.

Minimum size. The minimum overall dimensions
of reinforced concrete columns for fire-resistance
ratings of 1 hour to 4 hours shall comply with Table
721.2.4.

Minimum cover for R/C columns. The minimum
thickness of concrete cover to the main longitudinal
reinforcement in columns, regardless of the type of
aggregate used in the concrete, shall not be less than 1
inch (25 mm) times the number of hours of required fire
resistance or 2 inches (51 mm), whichever is less.

Columns built into walls. The minimum
dimensions of Table 721.2.4 do not apply to a reinforced
concrete column that is built into a concrete or masonry
wall provided all of the following are met:
1. The fire-resistance rating for the wall is equal to or
greater than the required rating of the column;
2. The main longitudinal reinforcing in the column
has cover not less than that required by Section
721.2.4.2; and
3. Openings in the wall are protected in accordance
with Table 715.4.
Where openings in the wall are not protected as
required by Section 715.4, the minimum dimension of
columns required to have a fire-resistance rating of 3
hours or less shall be 8 inches (203 mm), and 10 inches
(254 mm) for columns required to have a fire-resistance
rating of 4 hours, regardless of the type of aggregate used
in the concrete.

Precast cover units for steel columns. See
Section 721.5.1.4.

International Building Code 721.2.1

Concrete walls. Cast-in-place and precast concrete
walls shall comply with Section 721.2.1.1. Multiwythe concrete
walls shall comply with Section 721.2.1.2. Joints
between precast panels shall comply with Section
721.2.1.3. Concretewalls with gypsum wallboard or plaster
finish shall comply with Section 721.2.1.4.

Cast-in-place or precast walls. The minimum
equivalent thicknesses of cast-in-place or precast
concrete walls for fire-resistance ratings of 1 hour to 4
hours are shown in Table 721.2.1.1. For solid walls with
flat vertical surfaces, the equivalent thickness is the same
as the actual thickness. The values in Table 721.2.1.1
apply to plain, reinforced or prestressed concrete walls.

Hollow-core precast wall panels. For
hollow-core precast concretewall panels in which the
cores are of constant cross section throughout the
length, calculation of the equivalent thickness by
dividing the net cross-sectional area (the gross cross
section minus the area of the cores) of the panel by its
width shall be permitted.

Core spaces filled. Where all of the core
spaces of hollow-core wall panels are filled with
loose-fill material, such as expanded shale, clay, or
slag, or vermiculite or perlite, the fire-resistance rating
of the wall is the same as that of a solid wall of the
same concrete type and of the same overall thickness.

Tapered cross sections. The thickness of
panels with tapered cross sections shall be that determined
at a distance 2t or 6 inches (152 mm), whichever
is less, from the point of minimum thickness,
where t is the minimum thickness.

Ribbed or undulating surfaces. The
equivalent thickness of panels with ribbed or undulating
surfaces shall be determined by one of the
following expressions:
(Equation 7-3)
where:
s = Spacing of ribs or undulations.
t = Minimum thickness.
te = Equivalent thickness of the panel calculated as
the net cross-sectional area of the panel divided
by the width, in which the maximum thickness
used in the calculation shall not exceed 2t.

Multiwythe walls. For walls that consist of
two wythes of different types of concrete, the fire-resistance
ratings shall be permitted to be determined from
Figure 721.2.1.2.

Two or more wythes. The fire-resistance
rating forwall panels consisting of two or morewythes
shall be permitted to be determined by the formula:
(Equation 7-4)
where:
R = The fire endurance of the assembly, minutes.
R1, R2, and Rn = The fire endurances of the individual
wythes,minutes.Values ofRn
0.59 for use in Equation 7-4
are given in Table 721.2.1.2(1). Calculated fire-resistance
ratings are shown in Table 721.2.1.2(2).
2006 INTERNATIONAL BUILDING CODE 137
FIRE-RESISTANCE-RATED CONSTRUCTION
For SI: 1 inch = 25.4 mm.
FIGURE 721.2.1.2
FIRE-RESISTANCE RATINGS OF
TWO-WYTHE CONCRETE WALLS

Foam plastic insulation. The fire-resistance
ratings of precast concrete wall panels consisting
of a layer of foam plastic insulation sandwiched
between two wythes of concrete shall be permitted to
be determined by use of Equation 7-4. Foam plastic
insulation with a total thickness of less than 1 inch (25
mm) shall be disregarded. The Rn value for thickness
of foam plastic insulation of 1 inch (25 mm) or
greater, for use in the calculation, is 5 minutes; therefore
Rn
0.59 = 2.5.

Joints between precast wall panels. Joints
between precast concretewall panels which are not insulated
as required by this section shall be considered as
openings inwalls. Uninsulated joints shall be included in
determining the percentage of openings permitted by
Table 704.8. Where openings are not permitted or are
required by this code to be protected, the provisions of
this section shall be used to determine the amount of joint
insulation required. Insulated joints shall not be considered
openings for purposes of determining compliance
with the allowable percentage of openings in Table
704.8.

Ceramic fiber joint protection. Figure
721.2.1.3.1 shows thicknesses of ceramic fiber blankets
to be used to insulate joints between precast concretewall
panels for various panel thicknesses and for
joint widths of 3/8 inch (9.5 mm) and 1 inch (25 mm)
for fire-resistance ratings of 1 hour to 4 hours. For
joint widths between 3/8 inch (9.5 mm) and 1 inch (25
mm), the thickness of ceramic fiber blanket is allowed
to be determined by direct interpolation. Other tested
and labeled materials are acceptable in place of
ceramic fiber blankets.

Walls with gypsum wallboard or plaster finishes.
The fire-resistance rating of cast-in-place or precast
concrete walls with finishes of gypsum wallboard or
plaster applied to one or both sides shall be permitted to
be calculated in accordance with the provisions of this
section.

Nonfire-exposed side. Where the finish
of gypsum wallboard or plaster is applied to the side
of the wall not exposed to fire, the contribution of the
finish to the total fire-resistance rating shall be determined
as follows: The thickness of the finish shall
first be corrected by multiplying the actual thickness
of the finish by the applicable factor determined from
Table 721.2.1.4(1) based on the type of aggregate in
the concrete. The corrected thickness of finish shall
then be added to the actual or equivalent thickness of
concrete and fire-resistance rating of the concrete and
finish determined from Table 721.2.1.1, Figure
721.2.1.2 or Table 721.2.1.2(1).

Fire-exposed side. Where gypsum wallboard
or plaster is applied to the fire-exposed side of
the wall, the contribution of the finish to the total
fire-resistance rating shall be determined as follows:
The time assigned to the finish as established by Table
721.2.1.4(2) shall be added to the fire-resistance rating
determined from Table 721.2.1.1 or Figure 721.2.1.2,
or Table 721.2.1.2(1) for the concrete alone, or to the
rating determined in Section 721.2.1.4.1 for the concrete
and finish on the nonfire-exposed side.
138 2006 INTERNATIONAL BUILDING CODE
FIRE-RESISTANCE-RATED CONSTRUCTION

Nonsymmetrical assemblies. For a wall
having no finish on one side or different types or
thicknesses of finish on each side, the calculation procedures
of Sections 721.2.1.4.1 and 721.2.1.4.2 shall
be performed twice, assuming either side of the wall
to be the fire-exposed side. The fire-restance rating of
thewall shall not exceed the lower of the two values.
Exception: For an exterior wall with more than 5
feet (1524 mm) of horizontal separation, the fire
shall be assumed to occur on the interior side only.

Minimum concrete fire-resistance rating.
Where finishes applied to one or both sides of a
concrete wall contribute to the fire-resistance rating,
the concrete alone shall provide not less than one-half
of the total required fire-resistance rating. Additionally,
the contribution to the fire resistance of the finish
on the nonfire-exposed side of a load-bearingwall shall
not exceed one-half the contribution of the concrete
alone.

Concrete finishes. Finishes on concrete
walls that are assumed to contribute to the total
fire-resistance rating of thewall shall comply with the
installation requirements of Section 721.3.2.5.

International Building Code 721.2.1.1

Cast-in-place or precast walls. The minimum
equivalent thicknesses of cast-in-place or precast
concrete walls for fire-resistance ratings of 1 hour to 4
hours are shown in Table 721.2.1.1. For solid walls with
flat vertical surfaces, the equivalent thickness is the same
as the actual thickness. The values in Table 721.2.1.1
apply to plain, reinforced or prestressed concrete walls.

Hollow-core precast wall panels. For
hollow-core precast concretewall panels in which the
cores are of constant cross section throughout the
length, calculation of the equivalent thickness by
dividing the net cross-sectional area (the gross cross
section minus the area of the cores) of the panel by its
width shall be permitted.

Core spaces filled. Where all of the core
spaces of hollow-core wall panels are filled with
loose-fill material, such as expanded shale, clay, or
slag, or vermiculite or perlite, the fire-resistance rating
of the wall is the same as that of a solid wall of the
same concrete type and of the same overall thickness.

Tapered cross sections. The thickness of
panels with tapered cross sections shall be that determined
at a distance 2t or 6 inches (152 mm), whichever
is less, from the point of minimum thickness,
where t is the minimum thickness.

Ribbed or undulating surfaces. The
equivalent thickness of panels with ribbed or undulating
surfaces shall be determined by one of the
following expressions:
(Equation 7-3)
where:
s = Spacing of ribs or undulations.
t = Minimum thickness.
te = Equivalent thickness of the panel calculated as
the net cross-sectional area of the panel divided
by the width, in which the maximum thickness
used in the calculation shall not exceed 2t.

International Building Code 721.2.1.1.1

Hollow-core precast wall panels. For
hollow-core precast concretewall panels in which the
cores are of constant cross section throughout the
length, calculation of the equivalent thickness by
dividing the net cross-sectional area (the gross cross
section minus the area of the cores) of the panel by its
width shall be permitted.

International Building Code 721.2.1.1.2

Core spaces filled. Where all of the core
spaces of hollow-core wall panels are filled with
loose-fill material, such as expanded shale, clay, or
slag, or vermiculite or perlite, the fire-resistance rating
of the wall is the same as that of a solid wall of the
same concrete type and of the same overall thickness.

International Building Code 721.2.1.1.3

Tapered cross sections. The thickness of
panels with tapered cross sections shall be that determined
at a distance 2t or 6 inches (152 mm), whichever
is less, from the point of minimum thickness,
where t is the minimum thickness.

International Building Code 721.2.1.1.4

Ribbed or undulating surfaces. The
equivalent thickness of panels with ribbed or undulating
surfaces shall be determined by one of the
following expressions:
(Equation 7-3)
where:
s = Spacing of ribs or undulations.
t = Minimum thickness.
te = Equivalent thickness of the panel calculated as
the net cross-sectional area of the panel divided
by the width, in which the maximum thickness
used in the calculation shall not exceed 2t.

International Building Code 721.2.1.2

Multiwythe walls. For walls that consist of
two wythes of different types of concrete, the fire-resistance
ratings shall be permitted to be determined from
Figure 721.2.1.2.

Two or more wythes. The fire-resistance
rating forwall panels consisting of two or morewythes
shall be permitted to be determined by the formula:
(Equation 7-4)
where:
R = The fire endurance of the assembly, minutes.
R1, R2, and Rn = The fire endurances of the individual
wythes,minutes.Values ofRn
0.59 for use in Equation 7-4
are given in Table 721.2.1.2(1). Calculated fire-resistance
ratings are shown in Table 721.2.1.2(2).
2006 INTERNATIONAL BUILDING CODE 137
FIRE-RESISTANCE-RATED CONSTRUCTION
For SI: 1 inch = 25.4 mm.
FIGURE 721.2.1.2
FIRE-RESISTANCE RATINGS OF
TWO-WYTHE CONCRETE WALLS

Foam plastic insulation. The fire-resistance
ratings of precast concrete wall panels consisting
of a layer of foam plastic insulation sandwiched
between two wythes of concrete shall be permitted to
be determined by use of Equation 7-4. Foam plastic
insulation with a total thickness of less than 1 inch (25
mm) shall be disregarded. The Rn value for thickness
of foam plastic insulation of 1 inch (25 mm) or
greater, for use in the calculation, is 5 minutes; therefore
Rn
0.59 = 2.5.

International Building Code 721.2.1.2.1

Two or more wythes. The fire-resistance
rating forwall panels consisting of two or morewythes
shall be permitted to be determined by the formula:
(Equation 7-4)
where:
R = The fire endurance of the assembly, minutes.
R1, R2, and Rn = The fire endurances of the individual
wythes,minutes.Values ofRn
0.59 for use in Equation 7-4
are given in Table 721.2.1.2(1). Calculated fire-resistance
ratings are shown in Table 721.2.1.2(2).
2006 INTERNATIONAL BUILDING CODE 137
FIRE-RESISTANCE-RATED CONSTRUCTION
For SI: 1 inch = 25.4 mm.
FIGURE 721.2.1.2
FIRE-RESISTANCE RATINGS OF
TWO-WYTHE CONCRETE WALLS

International Building Code 721.2.1.2.2

Foam plastic insulation. The fire-resistance
ratings of precast concrete wall panels consisting
of a layer of foam plastic insulation sandwiched
between two wythes of concrete shall be permitted to
be determined by use of Equation 7-4. Foam plastic
insulation with a total thickness of less than 1 inch (25
mm) shall be disregarded. The Rn value for thickness
of foam plastic insulation of 1 inch (25 mm) or
greater, for use in the calculation, is 5 minutes; therefore
Rn
0.59 = 2.5.

International Building Code 721.2.1.3

Joints between precast wall panels. Joints
between precast concretewall panels which are not insulated
as required by this section shall be considered as
openings inwalls. Uninsulated joints shall be included in
determining the percentage of openings permitted by
Table 704.8. Where openings are not permitted or are
required by this code to be protected, the provisions of
this section shall be used to determine the amount of joint
insulation required. Insulated joints shall not be considered
openings for purposes of determining compliance
with the allowable percentage of openings in Table
704.8.

Ceramic fiber joint protection. Figure
721.2.1.3.1 shows thicknesses of ceramic fiber blankets
to be used to insulate joints between precast concretewall
panels for various panel thicknesses and for
joint widths of 3/8 inch (9.5 mm) and 1 inch (25 mm)
for fire-resistance ratings of 1 hour to 4 hours. For
joint widths between 3/8 inch (9.5 mm) and 1 inch (25
mm), the thickness of ceramic fiber blanket is allowed
to be determined by direct interpolation. Other tested
and labeled materials are acceptable in place of
ceramic fiber blankets.

International Building Code 721.2.1.3.1

Ceramic fiber joint protection. Figure
721.2.1.3.1 shows thicknesses of ceramic fiber blankets
to be used to insulate joints between precast concretewall
panels for various panel thicknesses and for
joint widths of 3/8 inch (9.5 mm) and 1 inch (25 mm)
for fire-resistance ratings of 1 hour to 4 hours. For
joint widths between 3/8 inch (9.5 mm) and 1 inch (25
mm), the thickness of ceramic fiber blanket is allowed
to be determined by direct interpolation. Other tested
and labeled materials are acceptable in place of
ceramic fiber blankets.

International Building Code 721.2.1.4

Walls with gypsum wallboard or plaster finishes.
The fire-resistance rating of cast-in-place or precast
concrete walls with finishes of gypsum wallboard or
plaster applied to one or both sides shall be permitted to
be calculated in accordance with the provisions of this
section.

Nonfire-exposed side. Where the finish
of gypsum wallboard or plaster is applied to the side
of the wall not exposed to fire, the contribution of the
finish to the total fire-resistance rating shall be determined
as follows: The thickness of the finish shall
first be corrected by multiplying the actual thickness
of the finish by the applicable factor determined from
Table 721.2.1.4(1) based on the type of aggregate in
the concrete. The corrected thickness of finish shall
then be added to the actual or equivalent thickness of
concrete and fire-resistance rating of the concrete and
finish determined from Table 721.2.1.1, Figure
721.2.1.2 or Table 721.2.1.2(1).

Fire-exposed side. Where gypsum wallboard
or plaster is applied to the fire-exposed side of
the wall, the contribution of the finish to the total
fire-resistance rating shall be determined as follows:
The time assigned to the finish as established by Table
721.2.1.4(2) shall be added to the fire-resistance rating
determined from Table 721.2.1.1 or Figure 721.2.1.2,
or Table 721.2.1.2(1) for the concrete alone, or to the
rating determined in Section 721.2.1.4.1 for the concrete
and finish on the nonfire-exposed side.
138 2006 INTERNATIONAL BUILDING CODE
FIRE-RESISTANCE-RATED CONSTRUCTION

Nonsymmetrical assemblies. For a wall
having no finish on one side or different types or
thicknesses of finish on each side, the calculation procedures
of Sections 721.2.1.4.1 and 721.2.1.4.2 shall
be performed twice, assuming either side of the wall
to be the fire-exposed side. The fire-restance rating of
thewall shall not exceed the lower of the two values.
Exception: For an exterior wall with more than 5
feet (1524 mm) of horizontal separation, the fire
shall be assumed to occur on the interior side only.

Minimum concrete fire-resistance rating.
Where finishes applied to one or both sides of a
concrete wall contribute to the fire-resistance rating,
the concrete alone shall provide not less than one-half
of the total required fire-resistance rating. Additionally,
the contribution to the fire resistance of the finish
on the nonfire-exposed side of a load-bearingwall shall
not exceed one-half the contribution of the concrete
alone.

Concrete finishes. Finishes on concrete
walls that are assumed to contribute to the total
fire-resistance rating of thewall shall comply with the
installation requirements of Section 721.3.2.5.

International Building Code 721.2.1.4.1

Nonfire-exposed side. Where the finish
of gypsum wallboard or plaster is applied to the side
of the wall not exposed to fire, the contribution of the
finish to the total fire-resistance rating shall be determined
as follows: The thickness of the finish shall
first be corrected by multiplying the actual thickness
of the finish by the applicable factor determined from
Table 721.2.1.4(1) based on the type of aggregate in
the concrete. The corrected thickness of finish shall
then be added to the actual or equivalent thickness of
concrete and fire-resistance rating of the concrete and
finish determined from Table 721.2.1.1, Figure
721.2.1.2 or Table 721.2.1.2(1).

International Building Code 721.2.1.4.2

Fire-exposed side. Where gypsum wallboard
or plaster is applied to the fire-exposed side of
the wall, the contribution of the finish to the total
fire-resistance rating shall be determined as follows:
The time assigned to the finish as established by Table
721.2.1.4(2) shall be added to the fire-resistance rating
determined from Table 721.2.1.1 or Figure 721.2.1.2,
or Table 721.2.1.2(1) for the concrete alone, or to the
rating determined in Section 721.2.1.4.1 for the concrete
and finish on the nonfire-exposed side.
138 2006 INTERNATIONAL BUILDING CODE
FIRE-RESISTANCE-RATED CONSTRUCTION

International Building Code 721.2.1.4.3

Nonsymmetrical assemblies. For a wall
having no finish on one side or different types or
thicknesses of finish on each side, the calculation procedures
of Sections 721.2.1.4.1 and 721.2.1.4.2 shall
be performed twice, assuming either side of the wall
to be the fire-exposed side. The fire-restance rating of
thewall shall not exceed the lower of the two values.
Exception: For an exterior wall with more than 5
feet (1524 mm) of horizontal separation, the fire
shall be assumed to occur on the interior side only.

International Building Code 721.2.1.4.4

Minimum concrete fire-resistance rating.
Where finishes applied to one or both sides of a
concrete wall contribute to the fire-resistance rating,
the concrete alone shall provide not less than one-half
of the total required fire-resistance rating. Additionally,
the contribution to the fire resistance of the finish
on the nonfire-exposed side of a load-bearingwall shall
not exceed one-half the contribution of the concrete
alone.

International Building Code 721.2.1.4.5

Concrete finishes. Finishes on concrete
walls that are assumed to contribute to the total
fire-resistance rating of thewall shall comply with the
installation requirements of Section 721.3.2.5.

International Building Code 721.2.2

Concrete floor and roof slabs. Reinforced and
prestressed floors and roofs shall comply with Section
721.2.2.1. Multicourse floors and roofs shall comply with
Sections 721.2.2.2 and 721.2.2.3, respectively.

Reinforced and prestressed floors and
roofs. The minimum thicknesses of reinforced and prestressed
concrete floor or roof slabs for fire-resistance
ratings of 1 hour to 4 hours are shown inTable 721.2.2.1.

Hollow-core prestressed slabs. For hollow-
core prestressed concrete slabs in which the cores
are of constant cross section throughout the length,
the equivalent thickness shall be permitted to be
obtained by dividing the net cross-sectional area of
the slab including grout in the joints, by its width.

Slabs with sloping soffits. The thickness
of slabs with sloping soffits (see Figure 721.2.2.1.2)
shall be determined at a distance 2t or 6 inches (152
mm), whichever is less, from the point of minimum
thickness, where t is the minimum thickness.

Slabs with ribbed soffits. The thickness
of slabs with ribbed or undulating soffits (see Figure
721.2.2.1.3) shall be determined by one of the following
expressions, whichever is applicable:
(Equation 7-5)
where:
s = Spacing of ribs or undulations.
t = Minimum thickness.
te = Equivalent thickness of the slab calculated as
the net area of the slab divided by the width, in
which the maximum thickness used in the calculation
shall not exceed 2t.

Multicourse floors. The fire-resistance ratings
of floors that consist of a base slab of concrete with a
topping (overlay) of a different type of concrete shall
comply with Figure 721.2.2.2.
140 2006 INTERNATIONAL BUILDING CODE
FIRE-RESISTANCE-RATED CONSTRUCTION
For SI: 1 inch = 25.4 mm.
FIGURE 721.2.2.1.3
SLABS WITH RIBBED OR UNDULATING SOFFITS
For SI: 1 inch = 25.4 mm.
FIGURE 721.2.2.1.2
DETERMINATION OF SLAB THICKNESS
FOR SLOPING SOFFITS

Multicourse roofs. The fire-resistance ratings
of roofs which consist of a base slab of concrete with a
topping (overlay) of an insulating concrete or with an
insulating board and built-up roofing shall comply with
Figures 721.2.2.3(1) and 721.2.2.3(2).

Heat transfer. For the transfer of heat,
three-ply built-up roofing contributes 10 minutes to
the fire-resistance rating. The fire-resistance rating
for concrete assemblies such as those shown in Figure
721.2.2.3(1) shall be increased by 10 minutes. This
increase is not applicable to those shown in Figure
721.2.2.3(2).

Joints in precast slabs. Joints between adjacent
precast concrete slabs need not be considered in calculating
the slab thickness provided that a concrete
topping at least 1 inch (25 mm) thick is used. Where no
concrete topping is used, joints must be grouted to a
depth of at least one-third the slab thickness at the joint,
but not less than 1 inch (25 mm), or the joints must be
made fire resistant by other approved methods.

International Building Code 721.2.2.1

Reinforced and prestressed floors and
roofs. The minimum thicknesses of reinforced and prestressed
concrete floor or roof slabs for fire-resistance
ratings of 1 hour to 4 hours are shown inTable 721.2.2.1.

Hollow-core prestressed slabs. For hollow-
core prestressed concrete slabs in which the cores
are of constant cross section throughout the length,
the equivalent thickness shall be permitted to be
obtained by dividing the net cross-sectional area of
the slab including grout in the joints, by its width.

Slabs with sloping soffits. The thickness
of slabs with sloping soffits (see Figure 721.2.2.1.2)
shall be determined at a distance 2t or 6 inches (152
mm), whichever is less, from the point of minimum
thickness, where t is the minimum thickness.

Slabs with ribbed soffits. The thickness
of slabs with ribbed or undulating soffits (see Figure
721.2.2.1.3) shall be determined by one of the following
expressions, whichever is applicable:
(Equation 7-5)
where:
s = Spacing of ribs or undulations.
t = Minimum thickness.
te = Equivalent thickness of the slab calculated as
the net area of the slab divided by the width, in
which the maximum thickness used in the calculation
shall not exceed 2t.

International Building Code 721.2.2.1.1

Hollow-core prestressed slabs. For hollow-
core prestressed concrete slabs in which the cores
are of constant cross section throughout the length,
the equivalent thickness shall be permitted to be
obtained by dividing the net cross-sectional area of
the slab including grout in the joints, by its width.

International Building Code 721.2.2.1.2

Slabs with sloping soffits. The thickness
of slabs with sloping soffits (see Figure 721.2.2.1.2)
shall be determined at a distance 2t or 6 inches (152
mm), whichever is less, from the point of minimum
thickness, where t is the minimum thickness.

International Building Code 721.2.2.1.3

Slabs with ribbed soffits. The thickness
of slabs with ribbed or undulating soffits (see Figure
721.2.2.1.3) shall be determined by one of the following
expressions, whichever is applicable:
(Equation 7-5)
where:
s = Spacing of ribs or undulations.
t = Minimum thickness.
te = Equivalent thickness of the slab calculated as
the net area of the slab divided by the width, in
which the maximum thickness used in the calculation
shall not exceed 2t.

International Building Code 721.2.2.2

Multicourse floors. The fire-resistance ratings
of floors that consist of a base slab of concrete with a
topping (overlay) of a different type of concrete shall
comply with Figure 721.2.2.2.
140 2006 INTERNATIONAL BUILDING CODE
FIRE-RESISTANCE-RATED CONSTRUCTION
For SI: 1 inch = 25.4 mm.
FIGURE 721.2.2.1.3
SLABS WITH RIBBED OR UNDULATING SOFFITS
For SI: 1 inch = 25.4 mm.
FIGURE 721.2.2.1.2
DETERMINATION OF SLAB THICKNESS
FOR SLOPING SOFFITS

International Building Code 721.2.2.3

Multicourse roofs. The fire-resistance ratings
of roofs which consist of a base slab of concrete with a
topping (overlay) of an insulating concrete or with an
insulating board and built-up roofing shall comply with
Figures 721.2.2.3(1) and 721.2.2.3(2).

Heat transfer. For the transfer of heat,
three-ply built-up roofing contributes 10 minutes to
the fire-resistance rating. The fire-resistance rating
for concrete assemblies such as those shown in Figure
721.2.2.3(1) shall be increased by 10 minutes. This
increase is not applicable to those shown in Figure
721.2.2.3(2).

International Building Code 721.2.2.3.1

Heat transfer. For the transfer of heat,
three-ply built-up roofing contributes 10 minutes to
the fire-resistance rating. The fire-resistance rating
for concrete assemblies such as those shown in Figure
721.2.2.3(1) shall be increased by 10 minutes. This
increase is not applicable to those shown in Figure
721.2.2.3(2).

International Building Code 721.2.2.4

Joints in precast slabs. Joints between adjacent
precast concrete slabs need not be considered in calculating
the slab thickness provided that a concrete
topping at least 1 inch (25 mm) thick is used. Where no
concrete topping is used, joints must be grouted to a
depth of at least one-third the slab thickness at the joint,
but not less than 1 inch (25 mm), or the joints must be
made fire resistant by other approved methods.

International Building Code 721.2.3

Concrete cover over reinforcement. The minimumthickness
of concrete cover over reinforcement in concrete
slabs, reinforced beams and prestressed beams shall
comply with this section.

Slab cover. The minimum thickness of concrete
cover to the positive moment reinforcement shall
comply with Table 721.2.3(1) for reinforced concrete
and Table 721.2.3(2) for prestressed concrete. These
tables are applicable for solid or hollow-core one-way or
two-way slabs with flat undersurfaces. These tables are
applicable to slabs that are either cast in place or precast.
For precast prestressed concrete not covered elsewhere,
the procedures contained in PCI MNL 124 shall be
acceptable.

Reinforced beam cover. The minimum thickness
of concrete cover to the positive moment reinforcement
(bottom steel) for reinforced concrete beams is
shown in Table 721.2.3(3) for fire-resistance ratings of 1
hour to 4 hours.

Prestressed beam cover. The minimum thickness
of concrete cover to the positive moment
prestressing tendons (bottom steel) for restrained and
unrestrained prestressed concrete beams and stemmed
units shall comply with the values shown in Tables
721.2.3(4) and 721.2.3(5) for fire-resistance ratings of 1
hour to 4 hours. Values in Table 721.2.3(4) apply to
beams 8 inches (203 mm) or greater in width. Values in
Table 721.2.3(5) apply to beams or stems of any width,
provided the cross-section area is not less than 40 square
inches (25 806 mm2). In case of differences between the
values determined from Table 721.2.3(4) or 721.2.3(5),
it is permitted to use the smaller value. The concrete
cover shall be calculated in accordance with Section
721.2.3.3.1. The minimum concrete cover for
nonprestressed reinforcement in prestressed concrete
beams shall comply with Section 721.2.3.2.

Calculating concrete cover. The concrete
cover for an individual tendon is the minimum
thickness of concrete between the surface of the tendon
and the fire-exposed surface of the beam, except
that for ungrouped ducts, the assumed cover thickness
is the minimum thickness of concrete between
the surface of the duct and the fire-exposed surface
of the beam. For beams in which two or more tendons
are used, the cover is assumed to be the average
of the minimum cover of the individual tendons. For
corner tendons (tendons equal distance from the bottom
and side), the minimum cover used in the calculation
shall be one-half the actual value. For
stemmed members with two or more prestressing
tendons located along the vertical centerline of the
stem, the average cover shall be the distance from the
bottomof the member to the centroid of the tendons.
The actual cover for any individual tendon shall not
be less than one-half the smaller value shown in
Tables 721.2.3(4) and 721.2.3(5), or 1 inch (25 mm),
whichever is greater.
2006 INTERNATIONAL BUILDING CODE 141
FIRE-RESISTANCE-RATED CONSTRUCTION
For SI: 1 inch = 25.4 mm.
FIGURE 721.2.2.2
FIRE-RESISTANCE RATINGS FOR TWO-COURSE
CONCRETE FLOORS
142 2006 INTERNATIONAL BUILDING CODE
FIRE-RESISTANCE-RATED CONSTRUCTION

International Building Code 721.2.3.1

Slab cover. The minimum thickness of concrete
cover to the positive moment reinforcement shall
comply with Table 721.2.3(1) for reinforced concrete
and Table 721.2.3(2) for prestressed concrete. These
tables are applicable for solid or hollow-core one-way or
two-way slabs with flat undersurfaces. These tables are
applicable to slabs that are either cast in place or precast.
For precast prestressed concrete not covered elsewhere,
the procedures contained in PCI MNL 124 shall be
acceptable.

International Building Code 721.2.3.2

Reinforced beam cover. The minimum thickness
of concrete cover to the positive moment reinforcement
(bottom steel) for reinforced concrete beams is
shown in Table 721.2.3(3) for fire-resistance ratings of 1
hour to 4 hours.

International Building Code 721.2.3.3

Prestressed beam cover. The minimum thickness
of concrete cover to the positive moment
prestressing tendons (bottom steel) for restrained and
unrestrained prestressed concrete beams and stemmed
units shall comply with the values shown in Tables
721.2.3(4) and 721.2.3(5) for fire-resistance ratings of 1
hour to 4 hours. Values in Table 721.2.3(4) apply to
beams 8 inches (203 mm) or greater in width. Values in
Table 721.2.3(5) apply to beams or stems of any width,
provided the cross-section area is not less than 40 square
inches (25 806 mm2). In case of differences between the
values determined from Table 721.2.3(4) or 721.2.3(5),
it is permitted to use the smaller value. The concrete
cover shall be calculated in accordance with Section
721.2.3.3.1. The minimum concrete cover for
nonprestressed reinforcement in prestressed concrete
beams shall comply with Section 721.2.3.2.

Calculating concrete cover. The concrete
cover for an individual tendon is the minimum
thickness of concrete between the surface of the tendon
and the fire-exposed surface of the beam, except
that for ungrouped ducts, the assumed cover thickness
is the minimum thickness of concrete between
the surface of the duct and the fire-exposed surface
of the beam. For beams in which two or more tendons
are used, the cover is assumed to be the average
of the minimum cover of the individual tendons. For
corner tendons (tendons equal distance from the bottom
and side), the minimum cover used in the calculation
shall be one-half the actual value. For
stemmed members with two or more prestressing
tendons located along the vertical centerline of the
stem, the average cover shall be the distance from the
bottomof the member to the centroid of the tendons.
The actual cover for any individual tendon shall not
be less than one-half the smaller value shown in
Tables 721.2.3(4) and 721.2.3(5), or 1 inch (25 mm),
whichever is greater.
2006 INTERNATIONAL BUILDING CODE 141
FIRE-RESISTANCE-RATED CONSTRUCTION
For SI: 1 inch = 25.4 mm.
FIGURE 721.2.2.2
FIRE-RESISTANCE RATINGS FOR TWO-COURSE
CONCRETE FLOORS
142 2006 INTERNATIONAL BUILDING CODE
FIRE-RESISTANCE-RATED CONSTRUCTION

International Building Code 721.2.3.3.1

Calculating concrete cover. The concrete
cover for an individual tendon is the minimum
thickness of concrete between the surface of the tendon
and the fire-exposed surface of the beam, except
that for ungrouped ducts, the assumed cover thickness
is the minimum thickness of concrete between
the surface of the duct and the fire-exposed surface
of the beam. For beams in which two or more tendons
are used, the cover is assumed to be the average
of the minimum cover of the individual tendons. For
corner tendons (tendons equal distance from the bottom
and side), the minimum cover used in the calculation
shall be one-half the actual value. For
stemmed members with two or more prestressing
tendons located along the vertical centerline of the
stem, the average cover shall be the distance from the
bottomof the member to the centroid of the tendons.
The actual cover for any individual tendon shall not
be less than one-half the smaller value shown in
Tables 721.2.3(4) and 721.2.3(5), or 1 inch (25 mm),
whichever is greater.
2006 INTERNATIONAL BUILDING CODE 141
FIRE-RESISTANCE-RATED CONSTRUCTION
For SI: 1 inch = 25.4 mm.
FIGURE 721.2.2.2
FIRE-RESISTANCE RATINGS FOR TWO-COURSE
CONCRETE FLOORS
142 2006 INTERNATIONAL BUILDING CODE
FIRE-RESISTANCE-RATED CONSTRUCTION

International Building Code 721.2.4

Concrete columns. Concrete columns shall comply
with this section.

Minimum size. The minimum overall dimensions
of reinforced concrete columns for fire-resistance
ratings of 1 hour to 4 hours shall comply with Table
721.2.4.

Minimum cover for R/C columns. The minimum
thickness of concrete cover to the main longitudinal
reinforcement in columns, regardless of the type of
aggregate used in the concrete, shall not be less than 1
inch (25 mm) times the number of hours of required fire
resistance or 2 inches (51 mm), whichever is less.

Columns built into walls. The minimum
dimensions of Table 721.2.4 do not apply to a reinforced
concrete column that is built into a concrete or masonry
wall provided all of the following are met:
1. The fire-resistance rating for the wall is equal to or
greater than the required rating of the column;
2. The main longitudinal reinforcing in the column
has cover not less than that required by Section
721.2.4.2; and
3. Openings in the wall are protected in accordance
with Table 715.4.
Where openings in the wall are not protected as
required by Section 715.4, the minimum dimension of
columns required to have a fire-resistance rating of 3
hours or less shall be 8 inches (203 mm), and 10 inches
(254 mm) for columns required to have a fire-resistance
rating of 4 hours, regardless of the type of aggregate used
in the concrete.

Precast cover units for steel columns. See
Section 721.5.1.4.

International Building Code 721.2.4.1

Minimum size. The minimum overall dimensions
of reinforced concrete columns for fire-resistance
ratings of 1 hour to 4 hours shall comply with Table
721.2.4.

International Building Code 721.2.4.2

Minimum cover for R/C columns. The minimum
thickness of concrete cover to the main longitudinal
reinforcement in columns, regardless of the type of
aggregate used in the concrete, shall not be less than 1
inch (25 mm) times the number of hours of required fire
resistance or 2 inches (51 mm), whichever is less.

International Building Code 721.2.4.3

Columns built into walls. The minimum
dimensions of Table 721.2.4 do not apply to a reinforced
concrete column that is built into a concrete or masonry
wall provided all of the following are met:
1. The fire-resistance rating for the wall is equal to or
greater than the required rating of the column;
2. The main longitudinal reinforcing in the column
has cover not less than that required by Section
721.2.4.2; and
3. Openings in the wall are protected in accordance
with Table 715.4.
Where openings in the wall are not protected as
required by Section 715.4, the minimum dimension of
columns required to have a fire-resistance rating of 3
hours or less shall be 8 inches (203 mm), and 10 inches
(254 mm) for columns required to have a fire-resistance
rating of 4 hours, regardless of the type of aggregate used
in the concrete.

International Building Code 721.2.4.4

Precast cover units for steel columns. See
Section 721.5.1.4.

International Building Code 721.3

Concrete masonry. The provisions of this section contain
procedures by which the fire-resistance ratings of concrete
masonry are established by calculations.

Equivalent thickness. The equivalent thickness of
concrete masonry construction shall be determined in
accordance with the provisions of this section.

Concrete masonry unit plus finishes. The
equivalent thickness of concrete masonry assemblies,
Tea, shall be computed as the sum of the equivalent thickness
of the concrete masonry unit, Te, as determined by
Section 721.3.1.2, 721.3.1.3, or 721.3.1.4, plus the
equivalent thickness of finishes, Tef, determined in accordance
with Section 721.3.2:
(Equation 7-6)
Te = Vn /LH = Equivalent thickness of concrete
masonry unit (inch) (mm).
where:
Vn = Net volume of masonry unit (inch3) (mm3).
L = Specified length of masonry unit (inch) (mm).
H = Specified height of masonry unit (inch) (mm).

Ungrouted or partially grouted construction.
Te shall be the value obtained for the concrete
masonry unit determined in accordance with ASTM C
140.

Solid grouted construction. The equivalent
thickness, Te, of solid grouted concrete masonry units is
the actual thickness of the unit.

Airspaces and cells filled with loose-fill
material. The equivalent thickness of completely filled
hollow concrete masonry is the actual thickness of the
unit when loose-fill materials are: sand, pea gravel,
crushed stone, or slag that meet ASTM C 33 requirements;
pumice, scoria, expanded shale, expanded clay,
expanded slate, expanded slag, expanded fly ash, or cinders
that comply withASTMC 331; or perlite or vermiculite
meeting the requirements of ASTM C 549 and
ASTM C 516, respectively.

Concrete masonry walls. The fire-resistance rating
of walls and partitions constructed of concrete masonry
units shall be determined from Table 721.3.2. The rating
shall be based on the equivalent thickness of the masonry
and type of aggregate used.

Finish on nonfire-exposed side. Where plaster
or gypsum wallboard is applied to the side of the wall
not exposed to fire, the contribution of the finish to the
total fire-resistance rating shall be determined as follows:
The thickness of gypsum wallboard or plaster shall
be corrected by multiplying the actual thickness of the
finish by applicable factor determined from Table
721.2.1.4(1). This corrected thickness of finish shall be
added to the equivalent thickness of masonry and the
fire-resistance rating of the masonry and finish determined
from Table 721.3.2.

Finish on fire-exposed side. Where plaster or
gypsum wallboard is applied to the fire-exposed side of
the wall, the contribution of the finish to the total
fire-resistance rating shall be determined as follows: The
time assigned to the finish as established by Table
721.2.1.4(2) shall be added to the fire-resistance rating
determined in Section 721.3.2 for the masonry alone, or
in Section 721.3.2.1 for the masonry and finish on the
nonfire-exposed side.
144 2006 INTERNATIONAL BUILDING CODE
FIRE-RESISTANCE-RATED CONSTRUCTION

Nonsymmetrical assemblies. For a wall having
no finish on one side or having different types or
thicknesses of finish on each side, the calculation procedures
of this section shall be performed twice, assuming
either side of the wall to be the fire-exposed side. The
fire-resistance rating of the wall shall not exceed the
lower of the two values calculated.
Exception: For exterior walls with more than 5 feet
(1524 mm) of horizontal separation, the fire shall be
assumed to occur on the interior side only.

Minimum concrete masonry fire-resistance
rating. Where the finish applied to a concrete masonry
wall contributes to its fire-resistance rating, the masonry
alone shall provide not less than one-half the total
required fire-resistance rating.

Attachment of finishes. Installation of finishes
shall be as follows:
1. Gypsum wallboard and gypsum lath applied to
concrete masonry or concrete walls shall be
secured to wood or steel furring members spaced
not more than 16 inches (406 mm)on center (o.c.).
2. Gypsum wallboard shall be installed with the long
dimension parallel to the furring members and
shall have all joints finished.
3. Other aspects of the installation of finishes shall
comply with the applicable provisions of Chapters
7 and 25.

Multiwythe masonry walls. The fire-resistance
rating of wall assemblies constructed of multiple wythes of
masonry materials shall be permitted to be based on the
fire-resistance rating period of each wythe and the continuous
airspace between each wythe in accordance with the following
formula:
(Equation 7-7)
where:
RA = Fire-resistance rating of the assembly (hours).
R1, R2, …, Rn = Fire-resistance rating of wythes for 1, 2, n
(hours), respectively.
A1, A2, …., An = 0.30, factor for each continuous airspace
for 1, 2, …n, respectively, having a depth of
1/2 inch (12.7 mm) or more between
wythes.

Concretemasonry lintels. Fire-resistance ratings for
concrete masonry lintels shall be determined based upon the
nominal thickness of the lintel and the minimum thickness of
concrete masonry or concrete, or any combination thereof,
covering the main reinforcing bars, as determined according
to Table 721.3.4, or by approved alternate methods.

Concrete masonry columns. The fire-resistance
rating of concrete masonry columns shall be determined
based upon the least plan dimension of the column in accordance
withTable 721.3.5 or by approved alternate methods.

International Building Code 721.3.1

Equivalent thickness. The equivalent thickness of
concrete masonry construction shall be determined in
accordance with the provisions of this section.

Concrete masonry unit plus finishes. The
equivalent thickness of concrete masonry assemblies,
Tea, shall be computed as the sum of the equivalent thickness
of the concrete masonry unit, Te, as determined by
Section 721.3.1.2, 721.3.1.3, or 721.3.1.4, plus the
equivalent thickness of finishes, Tef, determined in accordance
with Section 721.3.2:
(Equation 7-6)
Te = Vn /LH = Equivalent thickness of concrete
masonry unit (inch) (mm).
where:
Vn = Net volume of masonry unit (inch3) (mm3).
L = Specified length of masonry unit (inch) (mm).
H = Specified height of masonry unit (inch) (mm).

Ungrouted or partially grouted construction.
Te shall be the value obtained for the concrete
masonry unit determined in accordance with ASTM C
140.

Solid grouted construction. The equivalent
thickness, Te, of solid grouted concrete masonry units is
the actual thickness of the unit.

Airspaces and cells filled with loose-fill
material. The equivalent thickness of completely filled
hollow concrete masonry is the actual thickness of the
unit when loose-fill materials are: sand, pea gravel,
crushed stone, or slag that meet ASTM C 33 requirements;
pumice, scoria, expanded shale, expanded clay,
expanded slate, expanded slag, expanded fly ash, or cinders
that comply withASTMC 331; or perlite or vermiculite
meeting the requirements of ASTM C 549 and
ASTM C 516, respectively.

International Building Code 721.3.1.1

Concrete masonry unit plus finishes. The
equivalent thickness of concrete masonry assemblies,
Tea, shall be computed as the sum of the equivalent thickness
of the concrete masonry unit, Te, as determined by
Section 721.3.1.2, 721.3.1.3, or 721.3.1.4, plus the
equivalent thickness of finishes, Tef, determined in accordance
with Section 721.3.2:
(Equation 7-6)
Te = Vn /LH = Equivalent thickness of concrete
masonry unit (inch) (mm).
where:
Vn = Net volume of masonry unit (inch3) (mm3).
L = Specified length of masonry unit (inch) (mm).
H = Specified height of masonry unit (inch) (mm).

International Building Code 721.3.1.2

Ungrouted or partially grouted construction.
Te shall be the value obtained for the concrete
masonry unit determined in accordance with ASTM C
140.

International Building Code 721.3.1.3

Solid grouted construction. The equivalent
thickness, Te, of solid grouted concrete masonry units is
the actual thickness of the unit.

International Building Code 721.3.1.4

Airspaces and cells filled with loose-fill
material. The equivalent thickness of completely filled
hollow concrete masonry is the actual thickness of the
unit when loose-fill materials are: sand, pea gravel,
crushed stone, or slag that meet ASTM C 33 requirements;
pumice, scoria, expanded shale, expanded clay,
expanded slate, expanded slag, expanded fly ash, or cinders
that comply withASTMC 331; or perlite or vermiculite
meeting the requirements of ASTM C 549 and
ASTM C 516, respectively.

International Building Code 721.3.2

Concrete masonry walls. The fire-resistance rating
of walls and partitions constructed of concrete masonry
units shall be determined from Table 721.3.2. The rating
shall be based on the equivalent thickness of the masonry
and type of aggregate used.

Finish on nonfire-exposed side. Where plaster
or gypsum wallboard is applied to the side of the wall
not exposed to fire, the contribution of the finish to the
total fire-resistance rating shall be determined as follows:
The thickness of gypsum wallboard or plaster shall
be corrected by multiplying the actual thickness of the
finish by applicable factor determined from Table
721.2.1.4(1). This corrected thickness of finish shall be
added to the equivalent thickness of masonry and the
fire-resistance rating of the masonry and finish determined
from Table 721.3.2.

Finish on fire-exposed side. Where plaster or
gypsum wallboard is applied to the fire-exposed side of
the wall, the contribution of the finish to the total
fire-resistance rating shall be determined as follows: The
time assigned to the finish as established by Table
721.2.1.4(2) shall be added to the fire-resistance rating
determined in Section 721.3.2 for the masonry alone, or
in Section 721.3.2.1 for the masonry and finish on the
nonfire-exposed side.
144 2006 INTERNATIONAL BUILDING CODE
FIRE-RESISTANCE-RATED CONSTRUCTION

Nonsymmetrical assemblies. For a wall having
no finish on one side or having different types or
thicknesses of finish on each side, the calculation procedures
of this section shall be performed twice, assuming
either side of the wall to be the fire-exposed side. The
fire-resistance rating of the wall shall not exceed the
lower of the two values calculated.
Exception: For exterior walls with more than 5 feet
(1524 mm) of horizontal separation, the fire shall be
assumed to occur on the interior side only.

Minimum concrete masonry fire-resistance
rating. Where the finish applied to a concrete masonry
wall contributes to its fire-resistance rating, the masonry
alone shall provide not less than one-half the total
required fire-resistance rating.

Attachment of finishes. Installation of finishes
shall be as follows:
1. Gypsum wallboard and gypsum lath applied to
concrete masonry or concrete walls shall be
secured to wood or steel furring members spaced
not more than 16 inches (406 mm)on center (o.c.).
2. Gypsum wallboard shall be installed with the long
dimension parallel to the furring members and
shall have all joints finished.
3. Other aspects of the installation of finishes shall
comply with the applicable provisions of Chapters
7 and 25.

International Building Code 721.3.2.1

Finish on nonfire-exposed side. Where plaster
or gypsum wallboard is applied to the side of the wall
not exposed to fire, the contribution of the finish to the
total fire-resistance rating shall be determined as follows:
The thickness of gypsum wallboard or plaster shall
be corrected by multiplying the actual thickness of the
finish by applicable factor determined from Table
721.2.1.4(1). This corrected thickness of finish shall be
added to the equivalent thickness of masonry and the
fire-resistance rating of the masonry and finish determined
from Table 721.3.2.

International Building Code 721.3.2.2

Finish on fire-exposed side. Where plaster or
gypsum wallboard is applied to the fire-exposed side of
the wall, the contribution of the finish to the total
fire-resistance rating shall be determined as follows: The
time assigned to the finish as established by Table
721.2.1.4(2) shall be added to the fire-resistance rating
determined in Section 721.3.2 for the masonry alone, or
in Section 721.3.2.1 for the masonry and finish on the
nonfire-exposed side.
144 2006 INTERNATIONAL BUILDING CODE
FIRE-RESISTANCE-RATED CONSTRUCTION

International Building Code 721.3.2.3

Nonsymmetrical assemblies. For a wall having
no finish on one side or having different types or
thicknesses of finish on each side, the calculation procedures
of this section shall be performed twice, assuming
either side of the wall to be the fire-exposed side. The
fire-resistance rating of the wall shall not exceed the
lower of the two values calculated.
Exception: For exterior walls with more than 5 feet
(1524 mm) of horizontal separation, the fire shall be
assumed to occur on the interior side only.

International Building Code 721.3.2.4

Minimum concrete masonry fire-resistance
rating. Where the finish applied to a concrete masonry
wall contributes to its fire-resistance rating, the masonry
alone shall provide not less than one-half the total
required fire-resistance rating.

International Building Code 721.3.2.5

Attachment of finishes. Installation of finishes
shall be as follows:
1. Gypsum wallboard and gypsum lath applied to
concrete masonry or concrete walls shall be
secured to wood or steel furring members spaced
not more than 16 inches (406 mm)on center (o.c.).
2. Gypsum wallboard shall be installed with the long
dimension parallel to the furring members and
shall have all joints finished.
3. Other aspects of the installation of finishes shall
comply with the applicable provisions of Chapters
7 and 25.

International Building Code 721.3.3

Multiwythe masonry walls. The fire-resistance
rating of wall assemblies constructed of multiple wythes of
masonry materials shall be permitted to be based on the
fire-resistance rating period of each wythe and the continuous
airspace between each wythe in accordance with the following
formula:
(Equation 7-7)
where:
RA = Fire-resistance rating of the assembly (hours).
R1, R2, …, Rn = Fire-resistance rating of wythes for 1, 2, n
(hours), respectively.
A1, A2, …., An = 0.30, factor for each continuous airspace
for 1, 2, …n, respectively, having a depth of
1/2 inch (12.7 mm) or more between
wythes.

International Building Code 721.3.4

Concretemasonry lintels. Fire-resistance ratings for
concrete masonry lintels shall be determined based upon the
nominal thickness of the lintel and the minimum thickness of
concrete masonry or concrete, or any combination thereof,
covering the main reinforcing bars, as determined according
to Table 721.3.4, or by approved alternate methods.

International Building Code 721.3.5

Concrete masonry columns. The fire-resistance
rating of concrete masonry columns shall be determined
based upon the least plan dimension of the column in accordance
withTable 721.3.5 or by approved alternate methods.

International Building Code 721.4

Clay brick and tile masonry. The provisions of this section
contain procedures by which the fire-resistance ratings of
clay brick and tile masonry are established by calculations.
2006 INTERNATIONAL BUILDING CODE 145
FIRE-RESISTANCE-RATED CONSTRUCTION

Masonry walls. The fire-resistance rating of
masonry walls shall be based upon the equivalent thickness
as calculated in accordance with this section. The calculation
shall take into account finishes applied to the wall and
airspaces between wythes in multiwythe construction.

Equivalent thickness. The fire-resistance ratings
of walls or partitions constructed of solid or hollow
clay masonry units shall be determined from Table
721.4.1(1) or 721.4.1(2). The equivalent thickness of the
clay masonry unit shall be determined by Equation 7-8
when using Table 721.4.1(1). The fire-resistance rating
determined from Table 721.4.1(1) shall be permitted to
be used in the calculated fire-resistance rating procedure
in Section 721.4.2.
(Equation 7-8)
where:
Te = The equivalent thickness of the clay masonry unit
(inches).
Vn = The net volume of the clay masonry unit (inch3).
L = The specified length of the clay masonry unit
(inches).
H = The specified height of the clay masonry unit
(inches).

Hollow clay units. The equivalent thickness,
Te, shall be the value obtained for hollow clay
units as determined in accordance withASTMC67.

Solid grouted clay units. The equivalent
thickness of solid grouted clay masonry units shall be
taken as the actual thickness of the units.

Units with filled cores. The equivalent
thickness of the hollow clay masonry units is the
actual thickness of the unit when completely filled
with loose-fill materials of: sand, pea gravel, crushed
stone, or slag that meet ASTM C 33 requirements;
pumice, scoria, expanded shale, expanded clay,
expanded slate, expanded slag, expanded fly ash, or
cinders in compliance withASTMC331; or perlite or
vermiculite meeting the requirements of ASTM C
549 and ASTM C 516, respectively.

Plaster finishes. Where plaster is applied to
the wall, the total fire-resistance rating shall be determined
by the formula:
(Equation 7-9)
where:
R = The fire-resistance rating of the assembly (hours).
Rn = The fire-resistance rating of the individual wall
(hours).
pl = Coefficient for thickness of plaster.
Values for Rn
0.59 for use in Equation 7-9 are given in
Table 721.4.1(3). Coefficients for thickness of plaster
shall be selected from Table 721.4.1(4) based on the
actual thickness of plaster applied to the wall or partition
and whether one or two sides of the wall are plastered.

Multiwythe walls with airspace. Where a
continuous airspace separates multiple wythes of the
wall or partition, the total fire-resistance rating shall be
determined by the formula:
(Equation 7-10)
where:
R = The fire-resistance rating of the assembly
(hours).
R1, R2 and Rn= The fire-resistance rating of the individual
wythes (hours).
as = Coefficient for continuous airspace.
Values for Rn
0.59 for use in Equation 7-10 are given in
Table 721.4.1(3). The coefficient for each continuous
airspace of 1/2 inch to 31/2 inches (12.7 to 89 mm) separating
two individual wythes shall be 0.3.
146 2006 INTERNATIONAL BUILDING CODE
FIRE-RESISTANCE-RATED CONSTRUCTION

Nonsymmetrical assemblies. For a wall having
no finish on one side or having different types or
thicknesses of finish on each side, the calculation procedures
of this section shall be performed twice, assuming
either side to be the fire-exposed side of thewall. The fire
resistance of the wall shall not exceed the lower of the
two values determined.
Exception: For exterior walls with more than 5 feet
(1524 mm) of horizontal separation, the fire shall be
assumed to occur on the interior side only.

Multiwythe walls. The fire-resistance rating for
walls or partitions consisting of two or more dissimilar
wythes shall be permitted to be determined by the formula:
(Equation 7-11)
where:
R = The fire-resistance rating of the assembly
(hours).
R1, R2 and Rn = The fire-resistance rating of the individual
wythes (hours).
Values for Rn
0.59 for use in Equation 7-11 are given in
Table 721.4.1(3).
2006 INTERNATIONAL BUILDING CODE 147
FIRE-RESISTANCE-RATED CONSTRUCTION

Multiwythe walls of different material. For
walls that consist of two or more wythes of different
materials (concrete or concrete masonry units) in combination
with clay masonry units, the fire-resistance rating
of the different materials shall be permitted to be determined
from Table 721.2.1.1 for concrete; Table 721.3.2
for concrete masonry units or Table 721.4.1(1) or
721.4.1(2) for clay and tile masonry units.

Reinforced clay masonry lintels. Fire-resistance
ratings for clay masonry lintels shall be determined based
on the nominal width of the lintel and the minimum covering
for the longitudinal reinforcement in accordance with
Table 721.4.1(5).

Reinforced clay masonry columns. The fire-resistance
ratings shall be determined based on the last plan
dimension of the column in accordance with Table
721.4.1(6). The minimum cover for longitudinal reinforcement
shall be 2 inches (51 mm).

International Building Code 721.4.1

Masonry walls. The fire-resistance rating of
masonry walls shall be based upon the equivalent thickness
as calculated in accordance with this section. The calculation
shall take into account finishes applied to the wall and
airspaces between wythes in multiwythe construction.

Equivalent thickness. The fire-resistance ratings
of walls or partitions constructed of solid or hollow
clay masonry units shall be determined from Table
721.4.1(1) or 721.4.1(2). The equivalent thickness of the
clay masonry unit shall be determined by Equation 7-8
when using Table 721.4.1(1). The fire-resistance rating
determined from Table 721.4.1(1) shall be permitted to
be used in the calculated fire-resistance rating procedure
in Section 721.4.2.
(Equation 7-8)
where:
Te = The equivalent thickness of the clay masonry unit
(inches).
Vn = The net volume of the clay masonry unit (inch3).
L = The specified length of the clay masonry unit
(inches).
H = The specified height of the clay masonry unit
(inches).

Hollow clay units. The equivalent thickness,
Te, shall be the value obtained for hollow clay
units as determined in accordance withASTMC67.

Solid grouted clay units. The equivalent
thickness of solid grouted clay masonry units shall be
taken as the actual thickness of the units.

Units with filled cores. The equivalent
thickness of the hollow clay masonry units is the
actual thickness of the unit when completely filled
with loose-fill materials of: sand, pea gravel, crushed
stone, or slag that meet ASTM C 33 requirements;
pumice, scoria, expanded shale, expanded clay,
expanded slate, expanded slag, expanded fly ash, or
cinders in compliance withASTMC331; or perlite or
vermiculite meeting the requirements of ASTM C
549 and ASTM C 516, respectively.

Plaster finishes. Where plaster is applied to
the wall, the total fire-resistance rating shall be determined
by the formula:
(Equation 7-9)
where:
R = The fire-resistance rating of the assembly (hours).
Rn = The fire-resistance rating of the individual wall
(hours).
pl = Coefficient for thickness of plaster.
Values for Rn
0.59 for use in Equation 7-9 are given in
Table 721.4.1(3). Coefficients for thickness of plaster
shall be selected from Table 721.4.1(4) based on the
actual thickness of plaster applied to the wall or partition
and whether one or two sides of the wall are plastered.

Multiwythe walls with airspace. Where a
continuous airspace separates multiple wythes of the
wall or partition, the total fire-resistance rating shall be
determined by the formula:
(Equation 7-10)
where:
R = The fire-resistance rating of the assembly
(hours).
R1, R2 and Rn= The fire-resistance rating of the individual
wythes (hours).
as = Coefficient for continuous airspace.
Values for Rn
0.59 for use in Equation 7-10 are given in
Table 721.4.1(3). The coefficient for each continuous
airspace of 1/2 inch to 31/2 inches (12.7 to 89 mm) separating
two individual wythes shall be 0.3.
146 2006 INTERNATIONAL BUILDING CODE
FIRE-RESISTANCE-RATED CONSTRUCTION

Nonsymmetrical assemblies. For a wall having
no finish on one side or having different types or
thicknesses of finish on each side, the calculation procedures
of this section shall be performed twice, assuming
either side to be the fire-exposed side of thewall. The fire
resistance of the wall shall not exceed the lower of the
two values determined.
Exception: For exterior walls with more than 5 feet
(1524 mm) of horizontal separation, the fire shall be
assumed to occur on the interior side only.

International Building Code 721.4.1.1

Equivalent thickness. The fire-resistance ratings
of walls or partitions constructed of solid or hollow
clay masonry units shall be determined from Table
721.4.1(1) or 721.4.1(2). The equivalent thickness of the
clay masonry unit shall be determined by Equation 7-8
when using Table 721.4.1(1). The fire-resistance rating
determined from Table 721.4.1(1) shall be permitted to
be used in the calculated fire-resistance rating procedure
in Section 721.4.2.
(Equation 7-8)
where:
Te = The equivalent thickness of the clay masonry unit
(inches).
Vn = The net volume of the clay masonry unit (inch3).
L = The specified length of the clay masonry unit
(inches).
H = The specified height of the clay masonry unit
(inches).

Hollow clay units. The equivalent thickness,
Te, shall be the value obtained for hollow clay
units as determined in accordance withASTMC67.

Solid grouted clay units. The equivalent
thickness of solid grouted clay masonry units shall be
taken as the actual thickness of the units.

Units with filled cores. The equivalent
thickness of the hollow clay masonry units is the
actual thickness of the unit when completely filled
with loose-fill materials of: sand, pea gravel, crushed
stone, or slag that meet ASTM C 33 requirements;
pumice, scoria, expanded shale, expanded clay,
expanded slate, expanded slag, expanded fly ash, or
cinders in compliance withASTMC331; or perlite or
vermiculite meeting the requirements of ASTM C
549 and ASTM C 516, respectively.

International Building Code 721.4.1.1.1

Hollow clay units. The equivalent thickness,
Te, shall be the value obtained for hollow clay
units as determined in accordance withASTMC67.

International Building Code 721.4.1.1.2

Solid grouted clay units. The equivalent
thickness of solid grouted clay masonry units shall be
taken as the actual thickness of the units.

International Building Code 721.4.1.1.3

Units with filled cores. The equivalent
thickness of the hollow clay masonry units is the
actual thickness of the unit when completely filled
with loose-fill materials of: sand, pea gravel, crushed
stone, or slag that meet ASTM C 33 requirements;
pumice, scoria, expanded shale, expanded clay,
expanded slate, expanded slag, expanded fly ash, or
cinders in compliance withASTMC331; or perlite or
vermiculite meeting the requirements of ASTM C
549 and ASTM C 516, respectively.

International Building Code 721.4.1.2

Plaster finishes. Where plaster is applied to
the wall, the total fire-resistance rating shall be determined
by the formula:
(Equation 7-9)
where:
R = The fire-resistance rating of the assembly (hours).
Rn = The fire-resistance rating of the individual wall
(hours).
pl = Coefficient for thickness of plaster.
Values for Rn
0.59 for use in Equation 7-9 are given in
Table 721.4.1(3). Coefficients for thickness of plaster
shall be selected from Table 721.4.1(4) based on the
actual thickness of plaster applied to the wall or partition
and whether one or two sides of the wall are plastered.

International Building Code 721.4.1.3

Multiwythe walls with airspace. Where a
continuous airspace separates multiple wythes of the
wall or partition, the total fire-resistance rating shall be
determined by the formula:
(Equation 7-10)
where:
R = The fire-resistance rating of the assembly
(hours).
R1, R2 and Rn= The fire-resistance rating of the individual
wythes (hours).
as = Coefficient for continuous airspace.
Values for Rn
0.59 for use in Equation 7-10 are given in
Table 721.4.1(3). The coefficient for each continuous
airspace of 1/2 inch to 31/2 inches (12.7 to 89 mm) separating
two individual wythes shall be 0.3.
146 2006 INTERNATIONAL BUILDING CODE
FIRE-RESISTANCE-RATED CONSTRUCTION

International Building Code 721.4.1.4

Nonsymmetrical assemblies. For a wall having
no finish on one side or having different types or
thicknesses of finish on each side, the calculation procedures
of this section shall be performed twice, assuming
either side to be the fire-exposed side of thewall. The fire
resistance of the wall shall not exceed the lower of the
two values determined.
Exception: For exterior walls with more than 5 feet
(1524 mm) of horizontal separation, the fire shall be
assumed to occur on the interior side only.

International Building Code 721.4.2

Multiwythe walls. The fire-resistance rating for
walls or partitions consisting of two or more dissimilar
wythes shall be permitted to be determined by the formula:
(Equation 7-11)
where:
R = The fire-resistance rating of the assembly
(hours).
R1, R2 and Rn = The fire-resistance rating of the individual
wythes (hours).
Values for Rn
0.59 for use in Equation 7-11 are given in
Table 721.4.1(3).
2006 INTERNATIONAL BUILDING CODE 147
FIRE-RESISTANCE-RATED CONSTRUCTION

Multiwythe walls of different material. For
walls that consist of two or more wythes of different
materials (concrete or concrete masonry units) in combination
with clay masonry units, the fire-resistance rating
of the different materials shall be permitted to be determined
from Table 721.2.1.1 for concrete; Table 721.3.2
for concrete masonry units or Table 721.4.1(1) or
721.4.1(2) for clay and tile masonry units.

International Building Code 721.4.2.1

Multiwythe walls of different material. For
walls that consist of two or more wythes of different
materials (concrete or concrete masonry units) in combination
with clay masonry units, the fire-resistance rating
of the different materials shall be permitted to be determined
from Table 721.2.1.1 for concrete; Table 721.3.2
for concrete masonry units or Table 721.4.1(1) or
721.4.1(2) for clay and tile masonry units.

International Building Code 721.4.3

Reinforced clay masonry lintels. Fire-resistance
ratings for clay masonry lintels shall be determined based
on the nominal width of the lintel and the minimum covering
for the longitudinal reinforcement in accordance with
Table 721.4.1(5).

International Building Code 721.4.4

Reinforced clay masonry columns. The fire-resistance
ratings shall be determined based on the last plan
dimension of the column in accordance with Table
721.4.1(6). The minimum cover for longitudinal reinforcement
shall be 2 inches (51 mm).

International Building Code 721.5

Steel assemblies. The provisions of this section contain
procedures by which the fire-resistance ratings of steel assemblies
are established by calculations.

Structural steel columns. The fire-resistance ratings
of steel columns shall be based on the size of the element
and the type of protection provided in accordance with
this section.

General. These procedures establish a basis
for determining the fire resistance of column assemblies
as a function of the thickness of fire-resistant material
and, the weight,W, and heated perimeter, D, of steel columns.
As used in these sections,Wis the average weight
of a structural steel column in pounds per linear foot. The
heated perimeter, D, is the inside perimeter of the
fire-resistant material in inches as illustrated in Figure
721.5.1(1).

Nonload-bearing protection. The application
of these procedures shall be limited to column
assemblies in which the fire-resistant material is not
designed to carry any of the load acting on the column.

Embedments. In the absence of substantiating
fire-endurance test results, ducts, conduit, piping,
and similar mechanical, electrical, and plumbing
installations shall not be embedded in any required
fire-resistant materials.

Weight-to-perimeter ratio. Table
721.5.1(1) contains weight-to-heated-perimeter ratios
(W/D) for both contour and box fire-resistant profiles,
for the wide flange shapes most often used as columns.
For different fire-resistant protection profiles or column
cross sections, the weight-to-heated-perimeter
ratios (W/D) shall be determined in accordance with
the definitions given in this section.

Gypsum wallboard protection. The fire
resistance of structural steel columns with weightto-
heated-perimeter ratios (W/D) less than or equal to
3.65 and which are protected with Type X gypsum wallboard
shall be permitted to be determined from the following
expression:
(Equation 7-12)
where:
R = Fire resistance (minutes).
h = Total thickness of gypsum wallboard (inches).
D = Heated perimeter of the structural steel column
(inches).
W = Total weight of the structural steel column and
gypsum wallboard protection (pounds per linear
foot).
W = W+ 50hD/144.

Attachment. The gypsum wallboard
shall be supported as illustrated in either Figure
721.5.1(2) for fire-resistance ratings of 4 hours or
less, or Figure 721.5.1(3) for fire-resistance ratings of
3 hours or less.

Gypsum wallboard equivalent to concrete.
The determination of the fire resistance of
structural steel columns from Figure 721.5.1(4) is
permitted for various thicknesses of gypsum wallboard
as a function of the weight-to-heated-perimeter
ratio (W/D) of the column. For structural steel columns
with weight-to-heated-perimeter ratios (W/D)
greater than 3.65, the thickness of gypsum wallboard
required for specified fire-resistance ratings shall be
the same as the thickness determined for aW14 x 233
wide flange shape.

Spray-applied fire-resistant materials. The
fire resistance of wide-flange structural steel columns
protected with spray-applied fire-resistant materials, as
illustrated in Figure 721.5.1(5), shall be permitted to be
determined from the following expression:
148 2006 INTERNATIONAL BUILDING CODE
FIRE-RESISTANCE-RATED CONSTRUCTION
FIGURE 721.5.1(1)
DETERMINATION OF THE HEATED PERIMETER
OF STRUCTURAL STEEL COLUMNS
(Equation 7-13)
where:
R = Fire resistance (minutes).
h = Thickness of spray-applied fire-resistant material
(inches).
D = Heated perimeter of the structural steel column
(inches).
C1 and C2 = Material-dependent constants.
W = Weight of structural steel columns (pounds per linear
foot).
The fire resistance of structural steel columns protected
with intumescent or mastic fire-resistant coatings
shall be determined on the basis of fire-resistance tests in
accordance with Section 703.2.

Material-dependent constants. The
material-dependent constants, C1 and C2, shall be
determined for specific fire-resistant materials on the
basis of standard fire endurance tests in accordance
with Section 703.2. Unless evidence is submitted to
the building official substantiating a broader application,
this expression shall be limited to determining
the fire resistance of structural steel columns with
weight-to-heated-perimeter ratios (W/D) between the
largest and smallest columns for which standard
fire-resistance test results are available.

Spray-applied identification.
Spray-applied fire-resistant materials shall be identified
by density and thickness required for a given
fire-resistance rating.
2006 INTERNATIONAL BUILDING CODE 149
FIRE-RESISTANCE-RATED CONSTRUCTION
FIGURE 721.5.1(2)
GYPSUM WALLBOARD PROTECTED STRUCTURAL STEEL
COLUMNS WITH SHEET STEEL COLUMN COVERS
For SI: 1 inch = 25.4 mm, 1 foot = 305 mm.
1. Structural steel column, either wide flange or tubular shapes.
2. TypeX gypsumwallboard in accordance with ASTM C 36. For single-layer
applications, the wallboard shall be applied vertically with no horizontal
joints. For multiple-layer applications, horizontal joints are permitted at a
minimum spacing of 8 feet, provided that the joints in successive layers are
staggered at least 12 inches. The total required thickness of wallboard shall
be determined on the basis of the specified fire-resistance rating and the
weight-to-heated-perimeter ratio (W/D) of the column. For fire-resistance
ratings of 2 hours or less, one of the required layers of gypsum wallboard
may be applied to the exterior of the sheet steel column covers with 1-inchlong
Type S screws spaced 1 inch from the wallboard edge and 8 inches on
center. For such installations, 0.0149-inch minimum thickness galvanized
steel corner beads with 11/2-inch legs shall be attached to the wallboard with
Type S screws spaced 12 inches on center.
3. For fire-resistance ratings of 3 hours or less, the column covers shall be fabricated
from 0.0239-inch minimum thickness galvanized or stainless steel.
For 4-hour fire-resistance ratings, the column covers shall be fabricated from
0.0239-inch minimum thickness stainless steel. The column covers shall be
erected with the Snap Lock or Pittsburgh joint details.
For fire-resistance ratings of 2 hours or less, column covers fabricated from
0.0269-inch minimum thickness galvanized or stainless steel shall be permitted
to be erected with lap joints. The lap joints shall be permitted to be located
anywhere around the perimeter of the column cover. The lap joints shall be
secured with 1/2-inch-long No. 8 sheet metal screws spaced 12 inches on center.
The column covers shall be provided with a minimum expansion clearance
of 1/8 inch per linear foot between the ends of the cover and any restraining
construction.
FIGURE 721.5.1(3)
GYPSUM WALLBOARD PROTECTED STRUCTURAL STEEL
COLUMNS WITH STEEL STUD/SCREW ATTACHMENT SYSTEM
For SI: 1 inch = 25.4 mm, 1 foot = -305 mm.
1. Structural steel column, either wide flange or tubular shapes.
2. 15/8-inch deep studs fabricated from 0.0179-inch minimum thickness galvanized
steel with 15/16 or 17/16-inch legs. The length of the steel studs shall be
1/2 inch less than the height of the assembly.
3. TypeX gypsumwallboard in accordance with ASTM C 36. For single-layer
applications, the wallboard shall be applied vertically with no horizontal
joints. For multiple-layer applications, horizontal joints are permitted at a
minimum spacing of 8 feet, provided that the joints in successive layers are
staggered at least 12 inches. The total required thickness of wallboard shall
be determined on the basis of the specified fire-resistance rating and the
weight-to-heated-perimeter ratio (W/D) of the column.
4. Galvanized 0.0149-inch minimum thickness steel corner beads with
11/2-inch legs attached to the wallboard with 1-inch-long Type S screws
spaced 12 inches on center.
5. No. 18 SWG steel tie wires spaced 24 inches on center.
6. Sheet metal angles with 2-inch legs fabricated from 0.0221-inch minimum
thickness galvanized steel.
7. Type S screws, 1 inch long, shall be used for attaching the first layer of wallboard
to the steel studs and the third layer to the sheet metal angles at 24 inches
on center. Type S screws 13/4-inch long shall be used for attaching the second
layer of wallboard to the steel studs and the fourth layer to the sheet metal
angles at 12 inches on center. Type S screws 21/4 inches long shall be used for
attaching the third layer ofwallboard to the steel studs at 12 inches on center.

Concrete-protected columns. The fire resistance
of structural steel columns protected with concrete,
as illustrated in Figure 721.5.1(6) (a) and (b), shall be
permitted to be determined from the following expression:
(Equation 7-14)
where:
Ro=10(W/D) 0.7+17(h1.6/kc
0.2)#(1+26(H/pccch(L+h))0.8)
As used in these expressions:
R = Fire endurance at equilibrium moisture conditions
(minutes).
Ro = Fire endurance at zero moisture content (minutes).
m = Equilibrium moisture content of the concrete by
volume (percent).
W = Average weight of the steel column (pounds per
linear foot).
D = Heated perimeter of the steel column (inches).
h = Thickness of the concrete cover (inches).
kc = Ambient temperature thermal conductivity of the
concrete (Btu/hr ft F).
H = Ambient temperature thermal capacity of the steel
column = 0.11W (Btu/ ft F).
pc = Concrete density (pounds per cubic foot).
cc = Ambient temperature specific heat of concrete
(Btu/lb F).
L = Interior dimension of one side of a square concrete
box protection (inches).

Reentrant space filled. For wide-flange
steel columns completely encased in concrete with all
reentrant spaces filled [Figure 721.5.1(6)(c)], the
thermal capacity of the concrete within the reentrant
spaces shall be permitted to be added to the thermal
capacity of the steel column, as follows:
(Equation 7-15)
where:
bf = Flange width of the steel column (inches).
d = Depth of the steel column (inches).
As = Cross-sectional area of the steel column (square
inches).

Concrete properties unknown. If specific
data on the properties of concrete are not available,
the values given in Table 721.5.1(2) are
permitted.

Minimum concrete cover. For structural
steel column encased in concrete with all reentrant
spaces filled, Figure 721.5.1(6)(c) and Tables
721.5.1(7) and 721.5.1(8) indicate the thickness of
concrete cover required for various fire-resistance ratings
for typical wide-flange sections. The thicknesses
of concrete indicated in these tables also apply to
structural steel columns larger than those listed.
150 2006 INTERNATIONAL BUILDING CODE
FIRE-RESISTANCE-RATED CONSTRUCTION
For SI: 1 inch = 25.4 mm, 1 pound per linear foot/inch = 0.059 kg/m/mm.
FIGURE 721.5.1(4)
FIRE RESISTANCE OF STRUCTURAL STEEL COLUMNS
PROTECTED WITH VARIOUS THICKNESSES OF
TYPE X GYPSUM WALLBOARD
a. The W/D ratios for typical wide flange columns are listed in Table
721.5.1(1). For other column shapes, the W/D ratios shall be determined in
accordance with Section 720.5.1.1.
FIGURE 721.5.1(5)
WIDE FLANGE STRUCTURAL STEEL COLUMNS WITH
SPRAY-APPLIED FIRE-RESISTANT MATERIALS
FIGURE 721.5.1(6)
CONCRETE PROTECTED STRUCTURAL STEEL COLUMNSa,b
a. When the inside perimeter of the concrete protection is not square, L shall be
taken as the average of L1and L2. When the thickness of concrete cover is not
constant, h shall be taken as the average of h1 and h2.
b. Joints shall be protected with a minimum 1 inch thickness of ceramic fiber
blanket but in no case less than one-half the thickness of the column cover
(see Section 720.2.1.3).

Minimum precast concrete cover. For
structural steel columns protected with precast concrete
column covers as shown in Figure
721.5.1(6)(a), Tables 721.5.1(9) and 721.5.1(10)
indicate the thickness of the column covers required
for various fire-resistance ratings for typical
wide-flange shapes. The thicknesses of concrete
given in these tables also apply to structural steel columns
larger than those listed.

Masonry protection. The fire resistance
of structural steel columns protected with concrete
masonry units or clay masonry units as illustrated in
Figure 721.5.1(7), shall be permitted to be determined
from the following expression:
(Equation 7-16)
where:
R = Fire-resistance rating of column assembly
(hours).
W = Average weight of steel column (pounds per
foot).
D = Heated perimeter of steel column (inches) [see
Figure 721.5.1(7)].
Te = Equivalent thickness of concrete or clay
masonry unit (inches) (see Table 721.3.2 Note a
or Section 721.4.1).
K = Thermal conductivity of concrete or clay
masonry unit (Btu/hr ft F) [see Table
721.5.1(3)].
As = Cross-sectional area of steel column (square
inches).
dm = Density of the concrete or clay masonry unit
(pounds per cubic foot).
p = Inner perimeter of concrete or clay masonry
protection (inches) [see Figure 721.5.1(7)].

Equivalent concrete masonry thickness.
For structural steel columns protected with concrete
masonry, Table 721.5.1(5) gives the equivalent
thickness of concrete masonry required for various
fire-resistance ratings for typical column shapes. For
structural steel columns protected with clay masonry,
Table 721.5.1(6) gives the equivalent thickness of
concrete masonry required for various fire-resistance
ratings for typical column shapes.

Structural steel beams and girders. The
fire-resistance ratings of steel beams and girders shall be
based upon the size of the element and the type of protection
provided in accordance with this section.

Determination of fire resistance. These procedures
establish a basis for determining resistance of
structural steel beams and girders which differ in size
from that specified in approved fire-resistance-rated
assemblies as a function of the thickness of fire-resistant
material and the weight (W) and heated perimeter (D) of
the beam or girder. As used in these sections, W is the
average weight of a structural steel member in pounds
per linear foot (plf). The heated perimeter,D, is the inside
perimeter of the fire-resistant material in inches as illustrated
in Figure 721.5.2.

Weight-to-heated perimeter. The
weight-to-heated-perimeter ratios (W/D), for both
contour and box fire-resistant protection profiles, for
the wide flange shapes most often used as beams or
girders are given in Table 721.5.1(4). For different
shapes, the weight-to-heated-perimeter ratios (W/D)
shall be determined in accordance with the definitions
given in this section.

721.5.2.1.2 Beam and girder substitutions. Except
as provided for in Section 721.5.2.2, structural steel
beams in approved fire-resistance-rated assemblies
shall be considered the minimum permissible size.
Other beam or girder shapes shall be permitted to be
substituted provided that the weight-to-heated-perimeter
ratio (W/D) of the substitute beam is equal to or
greater than that of the beam specified in the approved
assembly.
2006 INTERNATIONAL BUILDING CODE 151
FIRE-RESISTANCE-RATED CONSTRUCTION
FIGURE 721.5.2
DETERMINATION OF THE HEATED PERIMETER
OF STRUCTURAL STEEL BEAMS AND GIRDERS
For SI: 1 inch = 25.4 mm.
FIGURE 721.5.1(7)
CONCRETE OR CLAY MASONRY PROTECTED
STRUCTURAL STEEL COLUMNS
d = Depth of a wide flange column, outside diameter of pipe column, or
outside dimension of structural tubing column (inches).
tweb = Thickness of web of wide flange column (inches).
w = Width of flange of wide flange column (inches).
152 2006 INTERNATIONAL BUILDING CODE
FIRE-RESISTANCE-RATED CONSTRUCTION

Spray-applied fire-resistant materials. The
provisions in this section apply to structural steel beams
and girders protected with spray-applied fire-resistant
materials. Larger or smaller beam and girder shapes shall
be permitted to be substituted for beams specified in
approved unrestrained or restrained fire-resistance-rated
assemblies, provided the thickness of the fire-resistant
material is adjusted in accordance with the following
expression:
(Equation 7-17)
where:
h =Thickness of spray-applied fire-resistant material
in inches.
W =Weight of the structural steel beam or girder in
pounds per linear foot.
D =Heated perimeter of the structural steel beam in
inches.
Subscript 1 refers to the beam and fire-resistant material
thickness in the approved assembly.
Subscript 2 refers to the substitute beam or girder and
the required thickness of fire-resistant material.
The fire resistance of structural steel beams and girders
protected with intumescent or mastic fire-resistant
coatings shall be determined on the basis of fire-resistance
tests in accordance with Section 703.2.

Minimum thickness. The use of Equation
7-17 is subject to the following conditions:
1. The weight-to-heated-perimeter ratio for the
substitute beam or girder (W2/D2) shall not be
less than 0.37.
2. The thickness of fire protection materials calculated
for the substitute beam or girder (T1) shall
not be less than 3/8 inch (9.5 mm).
3. The unrestrained or restrained beam rating shall
not be less than 1 hour.
4. When used to adjust the material thickness for a
restrained beam, the use of this procedure is
limited to steel sections classified as compact in
accordance with the AISC Specification for
Structural Steel Buildings, (AISC-LRFD).

Structural steel trusses. The fire resistance of
structural steel trusses protected with fire-resistant materials
spray-applied to each of the individual truss elements
shall be permitted to be determined in accordance
with this section. The thickness of the fire-resistant material
shall be determined in accordance with Section
721.5.1.3. The weight-to-heated-perimeter ratio (W/D)
of truss elements that can be simultaneously exposed to
fire on all sides shall be determined on the same basis as
columns, as specified in Section 721.5.1.1. The
weight-to-heated-perimeter ratio (W/D) of truss elements
that directly support floor or roof construction
shall be determined on the same basis as beams and girders,
as specified in Section 721.5.2.1.
The fire resistance of structural steel trusses protected
with intumescent or mastic fire-resistant coatings shall
be determined on the basis of fire-resistance tests in
accordance with Section 703.2.

International Building Code 721.5.1

Structural steel columns. The fire-resistance ratings
of steel columns shall be based on the size of the element
and the type of protection provided in accordance with
this section.

General. These procedures establish a basis
for determining the fire resistance of column assemblies
as a function of the thickness of fire-resistant material
and, the weight,W, and heated perimeter, D, of steel columns.
As used in these sections,Wis the average weight
of a structural steel column in pounds per linear foot. The
heated perimeter, D, is the inside perimeter of the
fire-resistant material in inches as illustrated in Figure
721.5.1(1).

Nonload-bearing protection. The application
of these procedures shall be limited to column
assemblies in which the fire-resistant material is not
designed to carry any of the load acting on the column.

Embedments. In the absence of substantiating
fire-endurance test results, ducts, conduit, piping,
and similar mechanical, electrical, and plumbing
installations shall not be embedded in any required
fire-resistant materials.

Weight-to-perimeter ratio. Table
721.5.1(1) contains weight-to-heated-perimeter ratios
(W/D) for both contour and box fire-resistant profiles,
for the wide flange shapes most often used as columns.
For different fire-resistant protection profiles or column
cross sections, the weight-to-heated-perimeter
ratios (W/D) shall be determined in accordance with
the definitions given in this section.

Gypsum wallboard protection. The fire
resistance of structural steel columns with weightto-
heated-perimeter ratios (W/D) less than or equal to
3.65 and which are protected with Type X gypsum wallboard
shall be permitted to be determined from the following
expression:
(Equation 7-12)
where:
R = Fire resistance (minutes).
h = Total thickness of gypsum wallboard (inches).
D = Heated perimeter of the structural steel column
(inches).
W = Total weight of the structural steel column and
gypsum wallboard protection (pounds per linear
foot).
W = W+ 50hD/144.

Attachment. The gypsum wallboard
shall be supported as illustrated in either Figure
721.5.1(2) for fire-resistance ratings of 4 hours or
less, or Figure 721.5.1(3) for fire-resistance ratings of
3 hours or less.

Gypsum wallboard equivalent to concrete.
The determination of the fire resistance of
structural steel columns from Figure 721.5.1(4) is
permitted for various thicknesses of gypsum wallboard
as a function of the weight-to-heated-perimeter
ratio (W/D) of the column. For structural steel columns
with weight-to-heated-perimeter ratios (W/D)
greater than 3.65, the thickness of gypsum wallboard
required for specified fire-resistance ratings shall be
the same as the thickness determined for aW14 x 233
wide flange shape.

Spray-applied fire-resistant materials. The
fire resistance of wide-flange structural steel columns
protected with spray-applied fire-resistant materials, as
illustrated in Figure 721.5.1(5), shall be permitted to be
determined from the following expression:
148 2006 INTERNATIONAL BUILDING CODE
FIRE-RESISTANCE-RATED CONSTRUCTION
FIGURE 721.5.1(1)
DETERMINATION OF THE HEATED PERIMETER
OF STRUCTURAL STEEL COLUMNS
(Equation 7-13)
where:
R = Fire resistance (minutes).
h = Thickness of spray-applied fire-resistant material
(inches).
D = Heated perimeter of the structural steel column
(inches).
C1 and C2 = Material-dependent constants.
W = Weight of structural steel columns (pounds per linear
foot).
The fire resistance of structural steel columns protected
with intumescent or mastic fire-resistant coatings
shall be determined on the basis of fire-resistance tests in
accordance with Section 703.2.

Material-dependent constants. The
material-dependent constants, C1 and C2, shall be
determined for specific fire-resistant materials on the
basis of standard fire endurance tests in accordance
with Section 703.2. Unless evidence is submitted to
the building official substantiating a broader application,
this expression shall be limited to determining
the fire resistance of structural steel columns with
weight-to-heated-perimeter ratios (W/D) between the
largest and smallest columns for which standard
fire-resistance test results are available.

Spray-applied identification.
Spray-applied fire-resistant materials shall be identified
by density and thickness required for a given
fire-resistance rating.
2006 INTERNATIONAL BUILDING CODE 149
FIRE-RESISTANCE-RATED CONSTRUCTION
FIGURE 721.5.1(2)
GYPSUM WALLBOARD PROTECTED STRUCTURAL STEEL
COLUMNS WITH SHEET STEEL COLUMN COVERS
For SI: 1 inch = 25.4 mm, 1 foot = 305 mm.
1. Structural steel column, either wide flange or tubular shapes.
2. TypeX gypsumwallboard in accordance with ASTM C 36. For single-layer
applications, the wallboard shall be applied vertically with no horizontal
joints. For multiple-layer applications, horizontal joints are permitted at a
minimum spacing of 8 feet, provided that the joints in successive layers are
staggered at least 12 inches. The total required thickness of wallboard shall
be determined on the basis of the specified fire-resistance rating and the
weight-to-heated-perimeter ratio (W/D) of the column. For fire-resistance
ratings of 2 hours or less, one of the required layers of gypsum wallboard
may be applied to the exterior of the sheet steel column covers with 1-inchlong
Type S screws spaced 1 inch from the wallboard edge and 8 inches on
center. For such installations, 0.0149-inch minimum thickness galvanized
steel corner beads with 11/2-inch legs shall be attached to the wallboard with
Type S screws spaced 12 inches on center.
3. For fire-resistance ratings of 3 hours or less, the column covers shall be fabricated
from 0.0239-inch minimum thickness galvanized or stainless steel.
For 4-hour fire-resistance ratings, the column covers shall be fabricated from
0.0239-inch minimum thickness stainless steel. The column covers shall be
erected with the Snap Lock or Pittsburgh joint details.
For fire-resistance ratings of 2 hours or less, column covers fabricated from
0.0269-inch minimum thickness galvanized or stainless steel shall be permitted
to be erected with lap joints. The lap joints shall be permitted to be located
anywhere around the perimeter of the column cover. The lap joints shall be
secured with 1/2-inch-long No. 8 sheet metal screws spaced 12 inches on center.
The column covers shall be provided with a minimum expansion clearance
of 1/8 inch per linear foot between the ends of the cover and any restraining
construction.
FIGURE 721.5.1(3)
GYPSUM WALLBOARD PROTECTED STRUCTURAL STEEL
COLUMNS WITH STEEL STUD/SCREW ATTACHMENT SYSTEM
For SI: 1 inch = 25.4 mm, 1 foot = -305 mm.
1. Structural steel column, either wide flange or tubular shapes.
2. 15/8-inch deep studs fabricated from 0.0179-inch minimum thickness galvanized
steel with 15/16 or 17/16-inch legs. The length of the steel studs shall be
1/2 inch less than the height of the assembly.
3. TypeX gypsumwallboard in accordance with ASTM C 36. For single-layer
applications, the wallboard shall be applied vertically with no horizontal
joints. For multiple-layer applications, horizontal joints are permitted at a
minimum spacing of 8 feet, provided that the joints in successive layers are
staggered at least 12 inches. The total required thickness of wallboard shall
be determined on the basis of the specified fire-resistance rating and the
weight-to-heated-perimeter ratio (W/D) of the column.
4. Galvanized 0.0149-inch minimum thickness steel corner beads with
11/2-inch legs attached to the wallboard with 1-inch-long Type S screws
spaced 12 inches on center.
5. No. 18 SWG steel tie wires spaced 24 inches on center.
6. Sheet metal angles with 2-inch legs fabricated from 0.0221-inch minimum
thickness galvanized steel.
7. Type S screws, 1 inch long, shall be used for attaching the first layer of wallboard
to the steel studs and the third layer to the sheet metal angles at 24 inches
on center. Type S screws 13/4-inch long shall be used for attaching the second
layer of wallboard to the steel studs and the fourth layer to the sheet metal
angles at 12 inches on center. Type S screws 21/4 inches long shall be used for
attaching the third layer ofwallboard to the steel studs at 12 inches on center.

Concrete-protected columns. The fire resistance
of structural steel columns protected with concrete,
as illustrated in Figure 721.5.1(6) (a) and (b), shall be
permitted to be determined from the following expression:
(Equation 7-14)
where:
Ro=10(W/D) 0.7+17(h1.6/kc
0.2)#(1+26(H/pccch(L+h))0.8)
As used in these expressions:
R = Fire endurance at equilibrium moisture conditions
(minutes).
Ro = Fire endurance at zero moisture content (minutes).
m = Equilibrium moisture content of the concrete by
volume (percent).
W = Average weight of the steel column (pounds per
linear foot).
D = Heated perimeter of the steel column (inches).
h = Thickness of the concrete cover (inches).
kc = Ambient temperature thermal conductivity of the
concrete (Btu/hr ft F).
H = Ambient temperature thermal capacity of the steel
column = 0.11W (Btu/ ft F).
pc = Concrete density (pounds per cubic foot).
cc = Ambient temperature specific heat of concrete
(Btu/lb F).
L = Interior dimension of one side of a square concrete
box protection (inches).

Reentrant space filled. For wide-flange
steel columns completely encased in concrete with all
reentrant spaces filled [Figure 721.5.1(6)(c)], the
thermal capacity of the concrete within the reentrant
spaces shall be permitted to be added to the thermal
capacity of the steel column, as follows:
(Equation 7-15)
where:
bf = Flange width of the steel column (inches).
d = Depth of the steel column (inches).
As = Cross-sectional area of the steel column (square
inches).

Concrete properties unknown. If specific
data on the properties of concrete are not available,
the values given in Table 721.5.1(2) are
permitted.

Minimum concrete cover. For structural
steel column encased in concrete with all reentrant
spaces filled, Figure 721.5.1(6)(c) and Tables
721.5.1(7) and 721.5.1(8) indicate the thickness of
concrete cover required for various fire-resistance ratings
for typical wide-flange sections. The thicknesses
of concrete indicated in these tables also apply to
structural steel columns larger than those listed.
150 2006 INTERNATIONAL BUILDING CODE
FIRE-RESISTANCE-RATED CONSTRUCTION
For SI: 1 inch = 25.4 mm, 1 pound per linear foot/inch = 0.059 kg/m/mm.
FIGURE 721.5.1(4)
FIRE RESISTANCE OF STRUCTURAL STEEL COLUMNS
PROTECTED WITH VARIOUS THICKNESSES OF
TYPE X GYPSUM WALLBOARD
a. The W/D ratios for typical wide flange columns are listed in Table
721.5.1(1). For other column shapes, the W/D ratios shall be determined in
accordance with Section 720.5.1.1.
FIGURE 721.5.1(5)
WIDE FLANGE STRUCTURAL STEEL COLUMNS WITH
SPRAY-APPLIED FIRE-RESISTANT MATERIALS
FIGURE 721.5.1(6)
CONCRETE PROTECTED STRUCTURAL STEEL COLUMNSa,b
a. When the inside perimeter of the concrete protection is not square, L shall be
taken as the average of L1and L2. When the thickness of concrete cover is not
constant, h shall be taken as the average of h1 and h2.
b. Joints shall be protected with a minimum 1 inch thickness of ceramic fiber
blanket but in no case less than one-half the thickness of the column cover
(see Section 720.2.1.3).

Minimum precast concrete cover. For
structural steel columns protected with precast concrete
column covers as shown in Figure
721.5.1(6)(a), Tables 721.5.1(9) and 721.5.1(10)
indicate the thickness of the column covers required
for various fire-resistance ratings for typical
wide-flange shapes. The thicknesses of concrete
given in these tables also apply to structural steel columns
larger than those listed.

Masonry protection. The fire resistance
of structural steel columns protected with concrete
masonry units or clay masonry units as illustrated in
Figure 721.5.1(7), shall be permitted to be determined
from the following expression:
(Equation 7-16)
where:
R = Fire-resistance rating of column assembly
(hours).
W = Average weight of steel column (pounds per
foot).
D = Heated perimeter of steel column (inches) [see
Figure 721.5.1(7)].
Te = Equivalent thickness of concrete or clay
masonry unit (inches) (see Table 721.3.2 Note a
or Section 721.4.1).
K = Thermal conductivity of concrete or clay
masonry unit (Btu/hr ft F) [see Table
721.5.1(3)].
As = Cross-sectional area of steel column (square
inches).
dm = Density of the concrete or clay masonry unit
(pounds per cubic foot).
p = Inner perimeter of concrete or clay masonry
protection (inches) [see Figure 721.5.1(7)].

Equivalent concrete masonry thickness.
For structural steel columns protected with concrete
masonry, Table 721.5.1(5) gives the equivalent
thickness of concrete masonry required for various
fire-resistance ratings for typical column shapes. For
structural steel columns protected with clay masonry,
Table 721.5.1(6) gives the equivalent thickness of
concrete masonry required for various fire-resistance
ratings for typical column shapes.

International Building Code 721.5.1.1

General. These procedures establish a basis
for determining the fire resistance of column assemblies
as a function of the thickness of fire-resistant material
and, the weight,W, and heated perimeter, D, of steel columns.
As used in these sections,Wis the average weight
of a structural steel column in pounds per linear foot. The
heated perimeter, D, is the inside perimeter of the
fire-resistant material in inches as illustrated in Figure
721.5.1(1).

Nonload-bearing protection. The application
of these procedures shall be limited to column
assemblies in which the fire-resistant material is not
designed to carry any of the load acting on the column.

Embedments. In the absence of substantiating
fire-endurance test results, ducts, conduit, piping,
and similar mechanical, electrical, and plumbing
installations shall not be embedded in any required
fire-resistant materials.

Weight-to-perimeter ratio. Table
721.5.1(1) contains weight-to-heated-perimeter ratios
(W/D) for both contour and box fire-resistant profiles,
for the wide flange shapes most often used as columns.
For different fire-resistant protection profiles or column
cross sections, the weight-to-heated-perimeter
ratios (W/D) shall be determined in accordance with
the definitions given in this section.

International Building Code 721.5.1.1.1

Nonload-bearing protection. The application
of these procedures shall be limited to column
assemblies in which the fire-resistant material is not
designed to carry any of the load acting on the column.

International Building Code 721.5.1.1.2

Embedments. In the absence of substantiating
fire-endurance test results, ducts, conduit, piping,
and similar mechanical, electrical, and plumbing
installations shall not be embedded in any required
fire-resistant materials.

International Building Code 721.5.1.1.3

Weight-to-perimeter ratio. Table
721.5.1(1) contains weight-to-heated-perimeter ratios
(W/D) for both contour and box fire-resistant profiles,
for the wide flange shapes most often used as columns.
For different fire-resistant protection profiles or column
cross sections, the weight-to-heated-perimeter
ratios (W/D) shall be determined in accordance with
the definitions given in this section.

International Building Code 721.5.1.2

Gypsum wallboard protection. The fire
resistance of structural steel columns with weightto-
heated-perimeter ratios (W/D) less than or equal to
3.65 and which are protected with Type X gypsum wallboard
shall be permitted to be determined from the following
expression:
(Equation 7-12)
where:
R = Fire resistance (minutes).
h = Total thickness of gypsum wallboard (inches).
D = Heated perimeter of the structural steel column
(inches).
W = Total weight of the structural steel column and
gypsum wallboard protection (pounds per linear
foot).
W = W+ 50hD/144.

Attachment. The gypsum wallboard
shall be supported as illustrated in either Figure
721.5.1(2) for fire-resistance ratings of 4 hours or
less, or Figure 721.5.1(3) for fire-resistance ratings of
3 hours or less.

Gypsum wallboard equivalent to concrete.
The determination of the fire resistance of
structural steel columns from Figure 721.5.1(4) is
permitted for various thicknesses of gypsum wallboard
as a function of the weight-to-heated-perimeter
ratio (W/D) of the column. For structural steel columns
with weight-to-heated-perimeter ratios (W/D)
greater than 3.65, the thickness of gypsum wallboard
required for specified fire-resistance ratings shall be
the same as the thickness determined for aW14 x 233
wide flange shape.

International Building Code 721.5.1.2.1

Attachment. The gypsum wallboard
shall be supported as illustrated in either Figure
721.5.1(2) for fire-resistance ratings of 4 hours or
less, or Figure 721.5.1(3) for fire-resistance ratings of
3 hours or less.

International Building Code 721.5.1.2.2

Gypsum wallboard equivalent to concrete.
The determination of the fire resistance of
structural steel columns from Figure 721.5.1(4) is
permitted for various thicknesses of gypsum wallboard
as a function of the weight-to-heated-perimeter
ratio (W/D) of the column. For structural steel columns
with weight-to-heated-perimeter ratios (W/D)
greater than 3.65, the thickness of gypsum wallboard
required for specified fire-resistance ratings shall be
the same as the thickness determined for aW14 x 233
wide flange shape.

International Building Code 721.5.1.3

Spray-applied fire-resistant materials. The
fire resistance of wide-flange structural steel columns
protected with spray-applied fire-resistant materials, as
illustrated in Figure 721.5.1(5), shall be permitted to be
determined from the following expression:
148 2006 INTERNATIONAL BUILDING CODE
FIRE-RESISTANCE-RATED CONSTRUCTION
FIGURE 721.5.1(1)
DETERMINATION OF THE HEATED PERIMETER
OF STRUCTURAL STEEL COLUMNS
(Equation 7-13)
where:
R = Fire resistance (minutes).
h = Thickness of spray-applied fire-resistant material
(inches).
D = Heated perimeter of the structural steel column
(inches).
C1 and C2 = Material-dependent constants.
W = Weight of structural steel columns (pounds per linear
foot).
The fire resistance of structural steel columns protected
with intumescent or mastic fire-resistant coatings
shall be determined on the basis of fire-resistance tests in
accordance with Section 703.2.

Material-dependent constants. The
material-dependent constants, C1 and C2, shall be
determined for specific fire-resistant materials on the
basis of standard fire endurance tests in accordance
with Section 703.2. Unless evidence is submitted to
the building official substantiating a broader application,
this expression shall be limited to determining
the fire resistance of structural steel columns with
weight-to-heated-perimeter ratios (W/D) between the
largest and smallest columns for which standard
fire-resistance test results are available.

Spray-applied identification.
Spray-applied fire-resistant materials shall be identified
by density and thickness required for a given
fire-resistance rating.
2006 INTERNATIONAL BUILDING CODE 149
FIRE-RESISTANCE-RATED CONSTRUCTION
FIGURE 721.5.1(2)
GYPSUM WALLBOARD PROTECTED STRUCTURAL STEEL
COLUMNS WITH SHEET STEEL COLUMN COVERS
For SI: 1 inch = 25.4 mm, 1 foot = 305 mm.
1. Structural steel column, either wide flange or tubular shapes.
2. TypeX gypsumwallboard in accordance with ASTM C 36. For single-layer
applications, the wallboard shall be applied vertically with no horizontal
joints. For multiple-layer applications, horizontal joints are permitted at a
minimum spacing of 8 feet, provided that the joints in successive layers are
staggered at least 12 inches. The total required thickness of wallboard shall
be determined on the basis of the specified fire-resistance rating and the
weight-to-heated-perimeter ratio (W/D) of the column. For fire-resistance
ratings of 2 hours or less, one of the required layers of gypsum wallboard
may be applied to the exterior of the sheet steel column covers with 1-inchlong
Type S screws spaced 1 inch from the wallboard edge and 8 inches on
center. For such installations, 0.0149-inch minimum thickness galvanized
steel corner beads with 11/2-inch legs shall be attached to the wallboard with
Type S screws spaced 12 inches on center.
3. For fire-resistance ratings of 3 hours or less, the column covers shall be fabricated
from 0.0239-inch minimum thickness galvanized or stainless steel.
For 4-hour fire-resistance ratings, the column covers shall be fabricated from
0.0239-inch minimum thickness stainless steel. The column covers shall be
erected with the Snap Lock or Pittsburgh joint details.
For fire-resistance ratings of 2 hours or less, column covers fabricated from
0.0269-inch minimum thickness galvanized or stainless steel shall be permitted
to be erected with lap joints. The lap joints shall be permitted to be located
anywhere around the perimeter of the column cover. The lap joints shall be
secured with 1/2-inch-long No. 8 sheet metal screws spaced 12 inches on center.
The column covers shall be provided with a minimum expansion clearance
of 1/8 inch per linear foot between the ends of the cover and any restraining
construction.
FIGURE 721.5.1(3)
GYPSUM WALLBOARD PROTECTED STRUCTURAL STEEL
COLUMNS WITH STEEL STUD/SCREW ATTACHMENT SYSTEM
For SI: 1 inch = 25.4 mm, 1 foot = -305 mm.
1. Structural steel column, either wide flange or tubular shapes.
2. 15/8-inch deep studs fabricated from 0.0179-inch minimum thickness galvanized
steel with 15/16 or 17/16-inch legs. The length of the steel studs shall be
1/2 inch less than the height of the assembly.
3. TypeX gypsumwallboard in accordance with ASTM C 36. For single-layer
applications, the wallboard shall be applied vertically with no horizontal
joints. For multiple-layer applications, horizontal joints are permitted at a
minimum spacing of 8 feet, provided that the joints in successive layers are
staggered at least 12 inches. The total required thickness of wallboard shall
be determined on the basis of the specified fire-resistance rating and the
weight-to-heated-perimeter ratio (W/D) of the column.
4. Galvanized 0.0149-inch minimum thickness steel corner beads with
11/2-inch legs attached to the wallboard with 1-inch-long Type S screws
spaced 12 inches on center.
5. No. 18 SWG steel tie wires spaced 24 inches on center.
6. Sheet metal angles with 2-inch legs fabricated from 0.0221-inch minimum
thickness galvanized steel.
7. Type S screws, 1 inch long, shall be used for attaching the first layer of wallboard
to the steel studs and the third layer to the sheet metal angles at 24 inches
on center. Type S screws 13/4-inch long shall be used for attaching the second
layer of wallboard to the steel studs and the fourth layer to the sheet metal
angles at 12 inches on center. Type S screws 21/4 inches long shall be used for
attaching the third layer ofwallboard to the steel studs at 12 inches on center.

International Building Code 721.5.1.3.1

Material-dependent constants. The
material-dependent constants, C1 and C2, shall be
determined for specific fire-resistant materials on the
basis of standard fire endurance tests in accordance
with Section 703.2. Unless evidence is submitted to
the building official substantiating a broader application,
this expression shall be limited to determining
the fire resistance of structural steel columns with
weight-to-heated-perimeter ratios (W/D) between the
largest and smallest columns for which standard
fire-resistance test results are available.

International Building Code 721.5.1.3.2

Spray-applied identification.
Spray-applied fire-resistant materials shall be identified
by density and thickness required for a given
fire-resistance rating.
2006 INTERNATIONAL BUILDING CODE 149
FIRE-RESISTANCE-RATED CONSTRUCTION
FIGURE 721.5.1(2)
GYPSUM WALLBOARD PROTECTED STRUCTURAL STEEL
COLUMNS WITH SHEET STEEL COLUMN COVERS
For SI: 1 inch = 25.4 mm, 1 foot = 305 mm.
1. Structural steel column, either wide flange or tubular shapes.
2. TypeX gypsumwallboard in accordance with ASTM C 36. For single-layer
applications, the wallboard shall be applied vertically with no horizontal
joints. For multiple-layer applications, horizontal joints are permitted at a
minimum spacing of 8 feet, provided that the joints in successive layers are
staggered at least 12 inches. The total required thickness of wallboard shall
be determined on the basis of the specified fire-resistance rating and the
weight-to-heated-perimeter ratio (W/D) of the column. For fire-resistance
ratings of 2 hours or less, one of the required layers of gypsum wallboard
may be applied to the exterior of the sheet steel column covers with 1-inchlong
Type S screws spaced 1 inch from the wallboard edge and 8 inches on
center. For such installations, 0.0149-inch minimum thickness galvanized
steel corner beads with 11/2-inch legs shall be attached to the wallboard with
Type S screws spaced 12 inches on center.
3. For fire-resistance ratings of 3 hours or less, the column covers shall be fabricated
from 0.0239-inch minimum thickness galvanized or stainless steel.
For 4-hour fire-resistance ratings, the column covers shall be fabricated from
0.0239-inch minimum thickness stainless steel. The column covers shall be
erected with the Snap Lock or Pittsburgh joint details.
For fire-resistance ratings of 2 hours or less, column covers fabricated from
0.0269-inch minimum thickness galvanized or stainless steel shall be permitted
to be erected with lap joints. The lap joints shall be permitted to be located
anywhere around the perimeter of the column cover. The lap joints shall be
secured with 1/2-inch-long No. 8 sheet metal screws spaced 12 inches on center.
The column covers shall be provided with a minimum expansion clearance
of 1/8 inch per linear foot between the ends of the cover and any restraining
construction.
FIGURE 721.5.1(3)
GYPSUM WALLBOARD PROTECTED STRUCTURAL STEEL
COLUMNS WITH STEEL STUD/SCREW ATTACHMENT SYSTEM
For SI: 1 inch = 25.4 mm, 1 foot = -305 mm.
1. Structural steel column, either wide flange or tubular shapes.
2. 15/8-inch deep studs fabricated from 0.0179-inch minimum thickness galvanized
steel with 15/16 or 17/16-inch legs. The length of the steel studs shall be
1/2 inch less than the height of the assembly.
3. TypeX gypsumwallboard in accordance with ASTM C 36. For single-layer
applications, the wallboard shall be applied vertically with no horizontal
joints. For multiple-layer applications, horizontal joints are permitted at a
minimum spacing of 8 feet, provided that the joints in successive layers are
staggered at least 12 inches. The total required thickness of wallboard shall
be determined on the basis of the specified fire-resistance rating and the
weight-to-heated-perimeter ratio (W/D) of the column.
4. Galvanized 0.0149-inch minimum thickness steel corner beads with
11/2-inch legs attached to the wallboard with 1-inch-long Type S screws
spaced 12 inches on center.
5. No. 18 SWG steel tie wires spaced 24 inches on center.
6. Sheet metal angles with 2-inch legs fabricated from 0.0221-inch minimum
thickness galvanized steel.
7. Type S screws, 1 inch long, shall be used for attaching the first layer of wallboard
to the steel studs and the third layer to the sheet metal angles at 24 inches
on center. Type S screws 13/4-inch long shall be used for attaching the second
layer of wallboard to the steel studs and the fourth layer to the sheet metal
angles at 12 inches on center. Type S screws 21/4 inches long shall be used for
attaching the third layer ofwallboard to the steel studs at 12 inches on center.

International Building Code 721.5.1.4

Concrete-protected columns. The fire resistance
of structural steel columns protected with concrete,
as illustrated in Figure 721.5.1(6) (a) and (b), shall be
permitted to be determined from the following expression:
(Equation 7-14)
where:
Ro=10(W/D) 0.7+17(h1.6/kc
0.2)#(1+26(H/pccch(L+h))0.8)
As used in these expressions:
R = Fire endurance at equilibrium moisture conditions
(minutes).
Ro = Fire endurance at zero moisture content (minutes).
m = Equilibrium moisture content of the concrete by
volume (percent).
W = Average weight of the steel column (pounds per
linear foot).
D = Heated perimeter of the steel column (inches).
h = Thickness of the concrete cover (inches).
kc = Ambient temperature thermal conductivity of the
concrete (Btu/hr ft F).
H = Ambient temperature thermal capacity of the steel
column = 0.11W (Btu/ ft F).
pc = Concrete density (pounds per cubic foot).
cc = Ambient temperature specific heat of concrete
(Btu/lb F).
L = Interior dimension of one side of a square concrete
box protection (inches).

Reentrant space filled. For wide-flange
steel columns completely encased in concrete with all
reentrant spaces filled [Figure 721.5.1(6)(c)], the
thermal capacity of the concrete within the reentrant
spaces shall be permitted to be added to the thermal
capacity of the steel column, as follows:
(Equation 7-15)
where:
bf = Flange width of the steel column (inches).
d = Depth of the steel column (inches).
As = Cross-sectional area of the steel column (square
inches).

Concrete properties unknown. If specific
data on the properties of concrete are not available,
the values given in Table 721.5.1(2) are
permitted.

Minimum concrete cover. For structural
steel column encased in concrete with all reentrant
spaces filled, Figure 721.5.1(6)(c) and Tables
721.5.1(7) and 721.5.1(8) indicate the thickness of
concrete cover required for various fire-resistance ratings
for typical wide-flange sections. The thicknesses
of concrete indicated in these tables also apply to
structural steel columns larger than those listed.
150 2006 INTERNATIONAL BUILDING CODE
FIRE-RESISTANCE-RATED CONSTRUCTION
For SI: 1 inch = 25.4 mm, 1 pound per linear foot/inch = 0.059 kg/m/mm.
FIGURE 721.5.1(4)
FIRE RESISTANCE OF STRUCTURAL STEEL COLUMNS
PROTECTED WITH VARIOUS THICKNESSES OF
TYPE X GYPSUM WALLBOARD
a. The W/D ratios for typical wide flange columns are listed in Table
721.5.1(1). For other column shapes, the W/D ratios shall be determined in
accordance with Section 720.5.1.1.
FIGURE 721.5.1(5)
WIDE FLANGE STRUCTURAL STEEL COLUMNS WITH
SPRAY-APPLIED FIRE-RESISTANT MATERIALS
FIGURE 721.5.1(6)
CONCRETE PROTECTED STRUCTURAL STEEL COLUMNSa,b
a. When the inside perimeter of the concrete protection is not square, L shall be
taken as the average of L1and L2. When the thickness of concrete cover is not
constant, h shall be taken as the average of h1 and h2.
b. Joints shall be protected with a minimum 1 inch thickness of ceramic fiber
blanket but in no case less than one-half the thickness of the column cover
(see Section 720.2.1.3).

Minimum precast concrete cover. For
structural steel columns protected with precast concrete
column covers as shown in Figure
721.5.1(6)(a), Tables 721.5.1(9) and 721.5.1(10)
indicate the thickness of the column covers required
for various fire-resistance ratings for typical
wide-flange shapes. The thicknesses of concrete
given in these tables also apply to structural steel columns
larger than those listed.

Masonry protection. The fire resistance
of structural steel columns protected with concrete
masonry units or clay masonry units as illustrated in
Figure 721.5.1(7), shall be permitted to be determined
from the following expression:
(Equation 7-16)
where:
R = Fire-resistance rating of column assembly
(hours).
W = Average weight of steel column (pounds per
foot).
D = Heated perimeter of steel column (inches) [see
Figure 721.5.1(7)].
Te = Equivalent thickness of concrete or clay
masonry unit (inches) (see Table 721.3.2 Note a
or Section 721.4.1).
K = Thermal conductivity of concrete or clay
masonry unit (Btu/hr ft F) [see Table
721.5.1(3)].
As = Cross-sectional area of steel column (square
inches).
dm = Density of the concrete or clay masonry unit
(pounds per cubic foot).
p = Inner perimeter of concrete or clay masonry
protection (inches) [see Figure 721.5.1(7)].

Equivalent concrete masonry thickness.
For structural steel columns protected with concrete
masonry, Table 721.5.1(5) gives the equivalent
thickness of concrete masonry required for various
fire-resistance ratings for typical column shapes. For
structural steel columns protected with clay masonry,
Table 721.5.1(6) gives the equivalent thickness of
concrete masonry required for various fire-resistance
ratings for typical column shapes.

International Building Code 721.5.1.4.1

Reentrant space filled. For wide-flange
steel columns completely encased in concrete with all
reentrant spaces filled [Figure 721.5.1(6)(c)], the
thermal capacity of the concrete within the reentrant
spaces shall be permitted to be added to the thermal
capacity of the steel column, as follows:
(Equation 7-15)
where:
bf = Flange width of the steel column (inches).
d = Depth of the steel column (inches).
As = Cross-sectional area of the steel column (square
inches).

International Building Code 721.5.1.4.2

Concrete properties unknown. If specific
data on the properties of concrete are not available,
the values given in Table 721.5.1(2) are
permitted.

International Building Code 721.5.1.4.3

Minimum concrete cover. For structural
steel column encased in concrete with all reentrant
spaces filled, Figure 721.5.1(6)(c) and Tables
721.5.1(7) and 721.5.1(8) indicate the thickness of
concrete cover required for various fire-resistance ratings
for typical wide-flange sections. The thicknesses
of concrete indicated in these tables also apply to
structural steel columns larger than those listed.
150 2006 INTERNATIONAL BUILDING CODE
FIRE-RESISTANCE-RATED CONSTRUCTION
For SI: 1 inch = 25.4 mm, 1 pound per linear foot/inch = 0.059 kg/m/mm.
FIGURE 721.5.1(4)
FIRE RESISTANCE OF STRUCTURAL STEEL COLUMNS
PROTECTED WITH VARIOUS THICKNESSES OF
TYPE X GYPSUM WALLBOARD
a. The W/D ratios for typical wide flange columns are listed in Table
721.5.1(1). For other column shapes, the W/D ratios shall be determined in
accordance with Section 720.5.1.1.
FIGURE 721.5.1(5)
WIDE FLANGE STRUCTURAL STEEL COLUMNS WITH
SPRAY-APPLIED FIRE-RESISTANT MATERIALS
FIGURE 721.5.1(6)
CONCRETE PROTECTED STRUCTURAL STEEL COLUMNSa,b
a. When the inside perimeter of the concrete protection is not square, L shall be
taken as the average of L1and L2. When the thickness of concrete cover is not
constant, h shall be taken as the average of h1 and h2.
b. Joints shall be protected with a minimum 1 inch thickness of ceramic fiber
blanket but in no case less than one-half the thickness of the column cover
(see Section 720.2.1.3).

International Building Code 721.5.1.4.4

Minimum precast concrete cover. For
structural steel columns protected with precast concrete
column covers as shown in Figure
721.5.1(6)(a), Tables 721.5.1(9) and 721.5.1(10)
indicate the thickness of the column covers required
for various fire-resistance ratings for typical
wide-flange shapes. The thicknesses of concrete
given in these tables also apply to structural steel columns
larger than those listed.

International Building Code 721.5.1.4.5

Masonry protection. The fire resistance
of structural steel columns protected with concrete
masonry units or clay masonry units as illustrated in
Figure 721.5.1(7), shall be permitted to be determined
from the following expression:
(Equation 7-16)
where:
R = Fire-resistance rating of column assembly
(hours).
W = Average weight of steel column (pounds per
foot).
D = Heated perimeter of steel column (inches) [see
Figure 721.5.1(7)].
Te = Equivalent thickness of concrete or clay
masonry unit (inches) (see Table 721.3.2 Note a
or Section 721.4.1).
K = Thermal conductivity of concrete or clay
masonry unit (Btu/hr ft F) [see Table
721.5.1(3)].
As = Cross-sectional area of steel column (square
inches).
dm = Density of the concrete or clay masonry unit
(pounds per cubic foot).
p = Inner perimeter of concrete or clay masonry
protection (inches) [see Figure 721.5.1(7)].

International Building Code 721.5.1.4.6

Equivalent concrete masonry thickness.
For structural steel columns protected with concrete
masonry, Table 721.5.1(5) gives the equivalent
thickness of concrete masonry required for various
fire-resistance ratings for typical column shapes. For
structural steel columns protected with clay masonry,
Table 721.5.1(6) gives the equivalent thickness of
concrete masonry required for various fire-resistance
ratings for typical column shapes.

International Building Code 721.5.2

Structural steel beams and girders. The
fire-resistance ratings of steel beams and girders shall be
based upon the size of the element and the type of protection
provided in accordance with this section.

Determination of fire resistance. These procedures
establish a basis for determining resistance of
structural steel beams and girders which differ in size
from that specified in approved fire-resistance-rated
assemblies as a function of the thickness of fire-resistant
material and the weight (W) and heated perimeter (D) of
the beam or girder. As used in these sections, W is the
average weight of a structural steel member in pounds
per linear foot (plf). The heated perimeter,D, is the inside
perimeter of the fire-resistant material in inches as illustrated
in Figure 721.5.2.

Weight-to-heated perimeter. The
weight-to-heated-perimeter ratios (W/D), for both
contour and box fire-resistant protection profiles, for
the wide flange shapes most often used as beams or
girders are given in Table 721.5.1(4). For different
shapes, the weight-to-heated-perimeter ratios (W/D)
shall be determined in accordance with the definitions
given in this section.

721.5.2.1.2 Beam and girder substitutions. Except
as provided for in Section 721.5.2.2, structural steel
beams in approved fire-resistance-rated assemblies
shall be considered the minimum permissible size.
Other beam or girder shapes shall be permitted to be
substituted provided that the weight-to-heated-perimeter
ratio (W/D) of the substitute beam is equal to or
greater than that of the beam specified in the approved
assembly.
2006 INTERNATIONAL BUILDING CODE 151
FIRE-RESISTANCE-RATED CONSTRUCTION
FIGURE 721.5.2
DETERMINATION OF THE HEATED PERIMETER
OF STRUCTURAL STEEL BEAMS AND GIRDERS
For SI: 1 inch = 25.4 mm.
FIGURE 721.5.1(7)
CONCRETE OR CLAY MASONRY PROTECTED
STRUCTURAL STEEL COLUMNS
d = Depth of a wide flange column, outside diameter of pipe column, or
outside dimension of structural tubing column (inches).
tweb = Thickness of web of wide flange column (inches).
w = Width of flange of wide flange column (inches).
152 2006 INTERNATIONAL BUILDING CODE
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Spray-applied fire-resistant materials. The
provisions in this section apply to structural steel beams
and girders protected with spray-applied fire-resistant
materials. Larger or smaller beam and girder shapes shall
be permitted to be substituted for beams specified in
approved unrestrained or restrained fire-resistance-rated
assemblies, provided the thickness of the fire-resistant
material is adjusted in accordance with the following
expression:
(Equation 7-17)
where:
h =Thickness of spray-applied fire-resistant material
in inches.
W =Weight of the structural steel beam or girder in
pounds per linear foot.
D =Heated perimeter of the structural steel beam in
inches.
Subscript 1 refers to the beam and fire-resistant material
thickness in the approved assembly.
Subscript 2 refers to the substitute beam or girder and
the required thickness of fire-resistant material.
The fire resistance of structural steel beams and girders
protected with intumescent or mastic fire-resistant
coatings shall be determined on the basis of fire-resistance
tests in accordance with Section 703.2.

Minimum thickness. The use of Equation
7-17 is subject to the following conditions:
1. The weight-to-heated-perimeter ratio for the
substitute beam or girder (W2/D2) shall not be
less than 0.37.
2. The thickness of fire protection materials calculated
for the substitute beam or girder (T1) shall
not be less than 3/8 inch (9.5 mm).
3. The unrestrained or restrained beam rating shall
not be less than 1 hour.
4. When used to adjust the material thickness for a
restrained beam, the use of this procedure is
limited to steel sections classified as compact in
accordance with the AISC Specification for
Structural Steel Buildings, (AISC-LRFD).

Structural steel trusses. The fire resistance of
structural steel trusses protected with fire-resistant materials
spray-applied to each of the individual truss elements
shall be permitted to be determined in accordance
with this section. The thickness of the fire-resistant material
shall be determined in accordance with Section
721.5.1.3. The weight-to-heated-perimeter ratio (W/D)
of truss elements that can be simultaneously exposed to
fire on all sides shall be determined on the same basis as
columns, as specified in Section 721.5.1.1. The
weight-to-heated-perimeter ratio (W/D) of truss elements
that directly support floor or roof construction
shall be determined on the same basis as beams and girders,
as specified in Section 721.5.2.1.
The fire resistance of structural steel trusses protected
with intumescent or mastic fire-resistant coatings shall
be determined on the basis of fire-resistance tests in
accordance with Section 703.2.

International Building Code 721.5.2.1

Determination of fire resistance. These procedures
establish a basis for determining resistance of
structural steel beams and girders which differ in size
from that specified in approved fire-resistance-rated
assemblies as a function of the thickness of fire-resistant
material and the weight (W) and heated perimeter (D) of
the beam or girder. As used in these sections, W is the
average weight of a structural steel member in pounds
per linear foot (plf). The heated perimeter,D, is the inside
perimeter of the fire-resistant material in inches as illustrated
in Figure 721.5.2.

Weight-to-heated perimeter. The
weight-to-heated-perimeter ratios (W/D), for both
contour and box fire-resistant protection profiles, for
the wide flange shapes most often used as beams or
girders are given in Table 721.5.1(4). For different
shapes, the weight-to-heated-perimeter ratios (W/D)
shall be determined in accordance with the definitions
given in this section.

721.5.2.1.2 Beam and girder substitutions. Except
as provided for in Section 721.5.2.2, structural steel
beams in approved fire-resistance-rated assemblies
shall be considered the minimum permissible size.
Other beam or girder shapes shall be permitted to be
substituted provided that the weight-to-heated-perimeter
ratio (W/D) of the substitute beam is equal to or
greater than that of the beam specified in the approved
assembly.
2006 INTERNATIONAL BUILDING CODE 151
FIRE-RESISTANCE-RATED CONSTRUCTION
FIGURE 721.5.2
DETERMINATION OF THE HEATED PERIMETER
OF STRUCTURAL STEEL BEAMS AND GIRDERS
For SI: 1 inch = 25.4 mm.
FIGURE 721.5.1(7)
CONCRETE OR CLAY MASONRY PROTECTED
STRUCTURAL STEEL COLUMNS
d = Depth of a wide flange column, outside diameter of pipe column, or
outside dimension of structural tubing column (inches).
tweb = Thickness of web of wide flange column (inches).
w = Width of flange of wide flange column (inches).
152 2006 INTERNATIONAL BUILDING CODE
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International Building Code 721.5.2.1.1

Weight-to-heated perimeter. The
weight-to-heated-perimeter ratios (W/D), for both
contour and box fire-resistant protection profiles, for
the wide flange shapes most often used as beams or
girders are given in Table 721.5.1(4). For different
shapes, the weight-to-heated-perimeter ratios (W/D)
shall be determined in accordance with the definitions
given in this section.

International Building Code 721.5.2.1.2

721.5.2.1.2 Beam and girder substitutions. Except
as provided for in Section 721.5.2.2, structural steel
beams in approved fire-resistance-rated assemblies
shall be considered the minimum permissible size.
Other beam or girder shapes shall be permitted to be
substituted provided that the weight-to-heated-perimeter
ratio (W/D) of the substitute beam is equal to or
greater than that of the beam specified in the approved
assembly.
2006 INTERNATIONAL BUILDING CODE 151
FIRE-RESISTANCE-RATED CONSTRUCTION
FIGURE 721.5.2
DETERMINATION OF THE HEATED PERIMETER
OF STRUCTURAL STEEL BEAMS AND GIRDERS
For SI: 1 inch = 25.4 mm.
FIGURE 721.5.1(7)
CONCRETE OR CLAY MASONRY PROTECTED
STRUCTURAL STEEL COLUMNS
d = Depth of a wide flange column, outside diameter of pipe column, or
outside dimension of structural tubing column (inches).
tweb = Thickness of web of wide flange column (inches).
w = Width of flange of wide flange column (inches).
152 2006 INTERNATIONAL BUILDING CODE
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International Building Code 721.5.2.2

Spray-applied fire-resistant materials. The
provisions in this section apply to structural steel beams
and girders protected with spray-applied fire-resistant
materials. Larger or smaller beam and girder shapes shall
be permitted to be substituted for beams specified in
approved unrestrained or restrained fire-resistance-rated
assemblies, provided the thickness of the fire-resistant
material is adjusted in accordance with the following
expression:
(Equation 7-17)
where:
h =Thickness of spray-applied fire-resistant material
in inches.
W =Weight of the structural steel beam or girder in
pounds per linear foot.
D =Heated perimeter of the structural steel beam in
inches.
Subscript 1 refers to the beam and fire-resistant material
thickness in the approved assembly.
Subscript 2 refers to the substitute beam or girder and
the required thickness of fire-resistant material.
The fire resistance of structural steel beams and girders
protected with intumescent or mastic fire-resistant
coatings shall be determined on the basis of fire-resistance
tests in accordance with Section 703.2.

Minimum thickness. The use of Equation
7-17 is subject to the following conditions:
1. The weight-to-heated-perimeter ratio for the
substitute beam or girder (W2/D2) shall not be
less than 0.37.
2. The thickness of fire protection materials calculated
for the substitute beam or girder (T1) shall
not be less than 3/8 inch (9.5 mm).
3. The unrestrained or restrained beam rating shall
not be less than 1 hour.
4. When used to adjust the material thickness for a
restrained beam, the use of this procedure is
limited to steel sections classified as compact in
accordance with the AISC Specification for
Structural Steel Buildings, (AISC-LRFD).

International Building Code 721.5.2.2.1

Minimum thickness. The use of Equation
7-17 is subject to the following conditions:
1. The weight-to-heated-perimeter ratio for the
substitute beam or girder (W2/D2) shall not be
less than 0.37.
2. The thickness of fire protection materials calculated
for the substitute beam or girder (T1) shall
not be less than 3/8 inch (9.5 mm).
3. The unrestrained or restrained beam rating shall
not be less than 1 hour.
4. When used to adjust the material thickness for a
restrained beam, the use of this procedure is
limited to steel sections classified as compact in
accordance with the AISC Specification for
Structural Steel Buildings, (AISC-LRFD).

International Building Code 721.5.2.3

Structural steel trusses. The fire resistance of
structural steel trusses protected with fire-resistant materials
spray-applied to each of the individual truss elements
shall be permitted to be determined in accordance
with this section. The thickness of the fire-resistant material
shall be determined in accordance with Section
721.5.1.3. The weight-to-heated-perimeter ratio (W/D)
of truss elements that can be simultaneously exposed to
fire on all sides shall be determined on the same basis as
columns, as specified in Section 721.5.1.1. The
weight-to-heated-perimeter ratio (W/D) of truss elements
that directly support floor or roof construction
shall be determined on the same basis as beams and girders,
as specified in Section 721.5.2.1.
The fire resistance of structural steel trusses protected
with intumescent or mastic fire-resistant coatings shall
be determined on the basis of fire-resistance tests in
accordance with Section 703.2.

International Building Code 721.6

Wood assemblies. The provisions of this section contain
procedures by which the fire-resistance ratings ofwood assemblies
are established by calculations.

General. This section contains procedures for calculating
the fire-resistance ratings of walls, floor/ceiling
and roof/ceiling assemblies based in part on the standard
method of testing referenced in Section 703.2.

Maximum fire-resistance rating. Fire-resistance
ratings calculated using the procedures in this section
shall be used only for 1-hour rated assemblies.

Dissimilar membranes. Where dissimilar
membranes are used on a wall assembly, the calculation
shall be made from the least fire-resistant (weaker) side.

Walls, floors and roofs. These procedures apply to
both load-bearing and nonload-bearing assemblies.

Fire-resistance rating ofwood frame assemblies.
The fire-resistance rating of a wood frame assembly
is equal to the sum of the time assigned to the
membrane on the fire-exposed side, the time assigned to
the framing members and the time assigned for additional
contribution by other protective measures such as
insulation. The membrane on the unexposed side shall
not be included in determining the fire resistance of the
assembly.

Time assigned to membranes. Table
721.6.2(1) indicates the time assigned to membranes on
the fire-exposed side.

Exterior walls. For an exterior wall having
more than 5 feet (1524 mm) of horizontal separation, the
wall is assigned a rating dependent on the interior membrane
and the framing as described in Tables 721.6.2(1)
and 721.6.2(2). The membrane on the outside of the
nonfire-exposed side of exterior walls having more than
5 feet (1524 mm) of horizontal separation may consist of
sheathing, sheathing paper, and siding as described in
Table 721.6.2(3).

Floors and roofs. In the case of a floor or roof,
the standard test provides only for testing for fire exposure
from below. Except as noted in Section 703.3, Item
5, floor or roof assemblies ofwood framing shall have an
upper membrane consisting of a subfloor and finished
floor conforming to Table 721.6.2(4) or any other membrane
that has a contribution to fire resistance of at least
15 minutes in Table 721.6.2(1).
2006 INTERNATIONAL BUILDING CODE 161
FIRE-RESISTANCE-RATED CONSTRUCTION

Additional protection. Table 721.6.2(5) indicates
the time increments to be added to the fire resistance
where glass fiber, rockwool, slag mineral wool, or
cellulose insulation is incorporated in the assembly.

Fastening. Fastening ofwood frame assemblies
and the fastening of membranes to the wood framing
members shall be done in accordance with Chapter 23.

Design of fire-resistant exposed wood members.
The fire-resistance rating, in minutes, of timber beams and
columns with a minimum nominal dimension of 6 inches
(152 mm) is equal to:
Beams: (Equation 7-18)
for beams which may be exposed
to fire on three sides.(Equation 7-19)
Columns: for columns which may be
exposed to fire on four sides (Equation 7-20)
for columns which may be
exposed to fire on three sides. (Equation 7-21)
where:
b = The breadth (width) of a beam or larger side of a
column before exposure to fire (inches).
d = The depth of a beam or smaller side of a column
before exposure to fire (inches).
Z = Load factor, based on Figure 721.6.3(1).
162 2006 INTERNATIONAL BUILDING CODE
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Equation 7-21. Equation 7-21 applies only
where the unexposed face represents the smaller side of
the column. If a column is recessed into a wall, its full
dimension shall be used for the purpose of these calculations.

Allowable loads. Allowable loads on beams
and columns are determined using design values given in
AF&PA NDS.

Fastener protection. Where minimum 1-hour
fire resistance is required, connectors and fasteners shall
be protected from fire exposure by 11/2 inches (38 mm) of
wood, or other approved covering or coating for a 1-hour
rating. Typical details for commonly used fasteners and
connectors are shown in AITC Technical Note 7

Minimum size.Wood members are limited to
dimensions of 6 inches (152 mm) nominal or greater.
Glued-laminated timber beams utilize standard laminating
combinations except that a core lamination is
removed. The tension zone is moved inward and the
equivalent of an extra nominal 2-inch-thick (51 mm)
outer tension lamination is added.
2006 INTERNATIONAL BUILDING CODE 163
FIRE-RESISTANCE-RATED CONSTRUCTION

International Building Code 721.6.1

General. This section contains procedures for calculating
the fire-resistance ratings of walls, floor/ceiling
and roof/ceiling assemblies based in part on the standard
method of testing referenced in Section 703.2.

Maximum fire-resistance rating. Fire-resistance
ratings calculated using the procedures in this section
shall be used only for 1-hour rated assemblies.

Dissimilar membranes. Where dissimilar
membranes are used on a wall assembly, the calculation
shall be made from the least fire-resistant (weaker) side.

International Building Code 721.6.1.1

Maximum fire-resistance rating. Fire-resistance
ratings calculated using the procedures in this section
shall be used only for 1-hour rated assemblies.

International Building Code 721.6.1.2

Dissimilar membranes. Where dissimilar
membranes are used on a wall assembly, the calculation
shall be made from the least fire-resistant (weaker) side.

International Building Code 721.6.2

Walls, floors and roofs. These procedures apply to
both load-bearing and nonload-bearing assemblies.

Fire-resistance rating ofwood frame assemblies.
The fire-resistance rating of a wood frame assembly
is equal to the sum of the time assigned to the
membrane on the fire-exposed side, the time assigned to
the framing members and the time assigned for additional
contribution by other protective measures such as
insulation. The membrane on the unexposed side shall
not be included in determining the fire resistance of the
assembly.

Time assigned to membranes. Table
721.6.2(1) indicates the time assigned to membranes on
the fire-exposed side.

Exterior walls. For an exterior wall having
more than 5 feet (1524 mm) of horizontal separation, the
wall is assigned a rating dependent on the interior membrane
and the framing as described in Tables 721.6.2(1)
and 721.6.2(2). The membrane on the outside of the
nonfire-exposed side of exterior walls having more than
5 feet (1524 mm) of horizontal separation may consist of
sheathing, sheathing paper, and siding as described in
Table 721.6.2(3).

Floors and roofs. In the case of a floor or roof,
the standard test provides only for testing for fire exposure
from below. Except as noted in Section 703.3, Item
5, floor or roof assemblies ofwood framing shall have an
upper membrane consisting of a subfloor and finished
floor conforming to Table 721.6.2(4) or any other membrane
that has a contribution to fire resistance of at least
15 minutes in Table 721.6.2(1).
2006 INTERNATIONAL BUILDING CODE 161
FIRE-RESISTANCE-RATED CONSTRUCTION

Additional protection. Table 721.6.2(5) indicates
the time increments to be added to the fire resistance
where glass fiber, rockwool, slag mineral wool, or
cellulose insulation is incorporated in the assembly.

Fastening. Fastening ofwood frame assemblies
and the fastening of membranes to the wood framing
members shall be done in accordance with Chapter 23.

International Building Code 721.6.2.1

Fire-resistance rating ofwood frame assemblies.
The fire-resistance rating of a wood frame assembly
is equal to the sum of the time assigned to the
membrane on the fire-exposed side, the time assigned to
the framing members and the time assigned for additional
contribution by other protective measures such as
insulation. The membrane on the unexposed side shall
not be included in determining the fire resistance of the
assembly.

International Building Code 721.6.2.2

Time assigned to membranes. Table
721.6.2(1) indicates the time assigned to membranes on
the fire-exposed side.

International Building Code 721.6.2.3

Exterior walls. For an exterior wall having
more than 5 feet (1524 mm) of horizontal separation, the
wall is assigned a rating dependent on the interior membrane
and the framing as described in Tables 721.6.2(1)
and 721.6.2(2). The membrane on the outside of the
nonfire-exposed side of exterior walls having more than
5 feet (1524 mm) of horizontal separation may consist of
sheathing, sheathing paper, and siding as described in
Table 721.6.2(3).

International Building Code 721.6.2.4

Floors and roofs. In the case of a floor or roof,
the standard test provides only for testing for fire exposure
from below. Except as noted in Section 703.3, Item
5, floor or roof assemblies ofwood framing shall have an
upper membrane consisting of a subfloor and finished
floor conforming to Table 721.6.2(4) or any other membrane
that has a contribution to fire resistance of at least
15 minutes in Table 721.6.2(1).
2006 INTERNATIONAL BUILDING CODE 161
FIRE-RESISTANCE-RATED CONSTRUCTION

International Building Code 721.6.2.5

Additional protection. Table 721.6.2(5) indicates
the time increments to be added to the fire resistance
where glass fiber, rockwool, slag mineral wool, or
cellulose insulation is incorporated in the assembly.

International Building Code 721.6.2.6

Fastening. Fastening ofwood frame assemblies
and the fastening of membranes to the wood framing
members shall be done in accordance with Chapter 23.

International Building Code 721.6.3

Design of fire-resistant exposed wood members.
The fire-resistance rating, in minutes, of timber beams and
columns with a minimum nominal dimension of 6 inches
(152 mm) is equal to:
Beams: (Equation 7-18)
for beams which may be exposed
to fire on three sides.(Equation 7-19)
Columns: for columns which may be
exposed to fire on four sides (Equation 7-20)
for columns which may be
exposed to fire on three sides. (Equation 7-21)
where:
b = The breadth (width) of a beam or larger side of a
column before exposure to fire (inches).
d = The depth of a beam or smaller side of a column
before exposure to fire (inches).
Z = Load factor, based on Figure 721.6.3(1).
162 2006 INTERNATIONAL BUILDING CODE
FIRE-RESISTANCE-RATED CONSTRUCTION

Equation 7-21. Equation 7-21 applies only
where the unexposed face represents the smaller side of
the column. If a column is recessed into a wall, its full
dimension shall be used for the purpose of these calculations.

Allowable loads. Allowable loads on beams
and columns are determined using design values given in
AF&PA NDS.

Fastener protection. Where minimum 1-hour
fire resistance is required, connectors and fasteners shall
be protected from fire exposure by 11/2 inches (38 mm) of
wood, or other approved covering or coating for a 1-hour
rating. Typical details for commonly used fasteners and
connectors are shown in AITC Technical Note 7

Minimum size.Wood members are limited to
dimensions of 6 inches (152 mm) nominal or greater.
Glued-laminated timber beams utilize standard laminating
combinations except that a core lamination is
removed. The tension zone is moved inward and the
equivalent of an extra nominal 2-inch-thick (51 mm)
outer tension lamination is added.
2006 INTERNATIONAL BUILDING CODE 163
FIRE-RESISTANCE-RATED CONSTRUCTION

International Building Code 721.6.3.1

Equation 7-21. Equation 7-21 applies only
where the unexposed face represents the smaller side of
the column. If a column is recessed into a wall, its full
dimension shall be used for the purpose of these calculations.

International Building Code 721.6.3.2

Allowable loads. Allowable loads on beams
and columns are determined using design values given in
AF&PA NDS.

International Building Code 721.6.3.3

Fastener protection. Where minimum 1-hour
fire resistance is required, connectors and fasteners shall
be protected from fire exposure by 11/2 inches (38 mm) of
wood, or other approved covering or coating for a 1-hour
rating. Typical details for commonly used fasteners and
connectors are shown in AITC Technical Note 7

International Building Code 721.6.3.4

Minimum size.Wood members are limited to
dimensions of 6 inches (152 mm) nominal or greater.
Glued-laminated timber beams utilize standard laminating
combinations except that a core lamination is
removed. The tension zone is moved inward and the
equivalent of an extra nominal 2-inch-thick (51 mm)
outer tension lamination is added.