Seismic Design Category
The seismic design category is a way of measuring the earthquake hazard in a given
region. Buildings are assigned a Seismic Design Category (SDC) in accordance with
their location on the
map shown in IRC Figure R301.2(2). Note the following:
- Buildings in SDC A & B are in the lowest seismic hazard regions and are exempt
from the seismic requirements of the IRC, as are detached one- and two-family dwellings
in SDC C (see Section R301.2.2). For buildings in these regions this calculator will determine wind bracing amounts only.
- Buildings located in SDC E are in the highest seismic hazard
regions and are not permitted to be designed using the IRC. The IRC and this calculator
will not evaluate buildings in SDC E (see Section R301.2.2.4).
- The U.S. Geological Survey (USGS) offers a calculation
tool to help determine the appropriate Seismic Design Category based on the project
site zip code or longitude and latitude. Go to the USGS website at Design Ground Motions (usgs.gov)
for more information.
- Contact the local building department to confirm the Seismic
Design Category.
Basic Wind Speed
The Basic Wind Speed is a design parameter that represents a home's potential exposure
to a hurricane, as determined by its location on
the map in IRC Figure R301.2(4). Note the following:
- This calculator evaluates the wind speeds included in IRC Table R602.10.1.2(1):
85 mph < 110 mph.
- Buildings located in regions where the basic wind speed
equals or exceeds 100 mph in hurricane-prone regions (Atlantic and Gulf of Mexico
coasts and several islands) or 110 mph elsewhere may not use the bracing provisions
of the IRC (see Section R301.2.1.1). It is the user's responsibility to verify that
IRC wind bracing provisions are acceptable where the basic wind speed equals or
exceeds 100 mph.
- Contact the local building department to confirm the Basic
Wind Speed.
Basic Wind Speed map
Click for larger version
Wind Exposure Category
The Wind Exposure Category reflects the characteristics of the ground surface surrounding
the home. If the home is surrounded by several similar-sized objects, then the wind
won't affect it as much as it would if the home were out in the open. The IRC defines
the following exposure categories (see Section R301.2.1.4):
- Exposure B: Urban and suburban areas, wooded areas, or other terrain with numerous
closely spaced obstructions having the size of single-family dwellings or larger.
Exposure B shall be assumed unless the site meets the definition of another type
exposure. The wind bracing amounts tabulated in the IRC are based on Exposure B.
- Exposure C: Open terrain with scattered obstructions, including
surface undulations or other irregularities, having heights generally less than
30 feet extending more than 1,500 feet from the building site in any quadrant. This
exposure shall also apply to any building located within Exposure B- type terrain
where the building is directly adjacent to open areas of Exposure C-type terrain
in any quadrant for a distance of more than 600 feet. This category includes flat
open country, grasslands and shorelines in hurricane-prone regions. Bracing in Exposure
C buildings will increase 20-40%.
- Exposure D: Flat, unobstructed areas exposed to wind flowing
over open water (excluding shorelines in hurricane-prone regions) for a distance
of at least 1 mile. Shorelines in Exposure D include inland waterways, the Great
Lakes and coastal areas of California, Oregon, Washington and Alaska. This exposure
shall apply only to those buildings and other structures exposed to the wind coming
from over the water. Exposure D extends inland from the shoreline a distance of
1,500 feet or 10 times the height of the building or structure, whichever is greater.
Buildings in Exposure D will have a 50-70% increase in bracing.
- Contact the local building department with questions about
which exposure to assume.
Number of Parallel Braced-Wall Lines
A minimum of two braced-wall lines are required in a given direction. Additional
braced-wall lines will reduce the spacing between braced-wall lines thereby greatly
reducing the tabulated wind bracing amounts. To compensate, an adjustment factor
must be applied to ensure the total amount of bracing in each direction is about
the same for a given structure regardless of the number of braced-wall lines (see
Table R602.10.1.2(1) footnote e). The seismic bracing amounts are not affected by
the number of parallel braced-wall lines.
Braced Wall Line Spacing “Average” Option
The 2012 IRC does not specify how to determine the spacing associated with a Braced Wall Line that
has parallel braced wall lines on both sides. In reference to the figure shown here, some jurisdictions
may require the spacing associated with BWL B to be the greater of the distance between A & B and B & C (34-ft).
This matches the requirements in the 2009 IRC but is conservative for most cases. Some jurisdictions may permit
the spacing associated with BWL B to be the average distance between A & B and B & C (28-ft), which typically
results in a lower amount of required bracing.
Supporting Stone or Masonry Veneer
Section R602.10.6.5 of the IRC requires method BV-WSP on “exterior braced wall lines and braced wall lines on the interior
of the building, backing or perpendicular to and laterally supporting veneered walls” when the stone or masonry veneer exceeds
the first-story height of detached one-or two-family dwellings in SDC D0, D1, or D2. In reference to the figure shown here,
Method BV-WSP must be used on BWLs 1, A, B, and C.
Braced-Wall-Line Location
The required wind and seismic bracing amounts in the IRC are increased as the number
of stories above the braced-wall line is increased (see Tables R602.10.1.2(1) and
R602.10.1.2(2)).
In some cases the number of stories above the braced-wall lines will be different
for braced-wall lines within the same story. One example would be a single-story
attached garage that is fully outside the perimeter of a two-story residence.
Eave-to-Ridge Height
Height measured from the top of the wall to the top of the roof ridge. The tabulated
bracing amounts in the IRC are based on a height of 10 feet. Increasing or decreasing
the height will increase or decrease the wind bracing amounts by as much as -30%
to +60% (see Table R602.10.1.2(1) footnote c). The seismic bracing amounts are not
affected by the eave-to-ridge height.
Stone or Masonry Veneer Exceeding 1st Story Height
In some cases, stone or masonry veneer that exceeds the 1st story level will increase
the required amount of seismic bracing and/or add new bracing requirements (see
Section R602.12). Wind bracing amounts are not affected by stone or masonry veneer.
See Section R703.7 for additional information on stone and masonry veneer.
Wall Dead Load
The tabulated seismic bracing amounts in the IRC are based on a 15 psf wall dead
load. Dead loads of 8 psf or less will decrease the required seismic bracing amounts
by 15% (see Table R602.10.1.2(3)). See Section R301.4 for determining dead loads.
A typical wood-stud partition wall with 1/2-inch gypsum board on both sides has
an estimated dead load of 8 psf. A typical exterior wood-stud wall has an estimated
dead load greater than 8 psf. See ASCE 7-05 standard and commentary for additional
information.
Wind bracing amounts are not affected by wall dead load.
Roof/Ceiling Dead Load
The tabulated seismic bracing amounts in the IRC are based on a 15 psf Roof/Ceiling
Dead Load. Larger dead loads will increase the required seismic bracing amounts
up to 20% (see Table R602.10.1.2(3)). See Section R301.4 for determining dead loads.
A typical asphalt shingle roof/ceiling assembly has an estimated dead load of 15
psf or less. Heavier roof coverings such as clay or concrete tile may result in
a roof/ceiling dead load greater than 15 psf. See ASCE 7-05 standard and commentary
for additional information.
Wind bracing amounts are not affected by roof/ceiling dead load.
Braced-Wall-Line Spacing
The distance between adjacent, parallel braced-wall lines. The spacing for braced
wall lines that have parallel braced-wall lines on both sides is the greater of
the distance between each braced-wall line (see Figure R602.10.1.4(4)).
The maximum braced-wall-line spacing for all buildings in SDC A and B and detached
one- or two-family dwellings in SDC C is 60 feet (see Table R602.10.1.2(1)). The
maximum spacing for townhouses in SDC C is 50 feet (see Table R602.10.1.2(3)). The
maximum spacing for all buildings in SDC D0, D1, and D2 is 25 feet with an exception
that permits a single spacing up to 35 feet (see Section R602.10.1.5).
This calculator evaluates the parameters entered and limits the maximum spacing
to 60, 50, or 35 feet on center and adjusts bracing amounts accordingly. For buildings
in SDC D0, D1, and D2 the user must ensure Braced-Wall-Line Spacing greater than
25 feet is acceptable.
Braced-Wall-Line Length
The distance between the ends of the braced-wall line. The end of a braced wall
line is considered to be the maximum length resulting from: a) the intersection
with perpendicular exterior walls or b) the intersection with perpendicular braced
wall lines (see Section R602.10.1).
The longer a braced-wall line, the more mass that wall line must support. Seismic
bracing amounts are increased linearly as braced-wall line length is increased.
Wind bracing amounts are not affected by braced-wall line length.
Wall Height
Wall height shall be the vertical distance from the lower edge of the bottom plate to the upper edge of the upper top plate.
As wall height is increased the wind surface area increases and the mass of the
wall increases. The tabulated wind and seismic bracing amounts are based on a wall
height of 10 feet. Shorter wall heights will reduce the required amount of wind
bracing by up to 10%. Taller wall heights will increase the required amount of wind
and seismic bracing by up to 20%. See Section R301.3, Table R602.10.1.2(1) footnote
d, and Table R602.10.1.2(3) for more information.
Bracing Method
The building codes define various construction methods that may be used to build
a code-compliant braced wall panel:
The required amount of wind and seismic bracing is dependent on the method of wall
bracing used. Generally, methods LIB (let-in-bracing) and GB (gypsum board) are
considered the weakest, method CS (continuous sheathing) is considered the strongest,
and the other methods are in between.
Eight intermittent methods and three narrow alternates are described in Table R602.10.2.
Continuous sheathing methods are described in Table R602.10.4.1. Stone or masonry
veneer exceeding the 1st story height in higher SDC regions requires wood structural
panel sheathing and holdowns installed in accordance with Section R602.12.1.3 and
is indicated in this calculator as method BV-WSP.
When mixing bracing methods, the user must ensure the following limits are satisfied
(see Section R602.10.1.1):
- Mixing bracing methods from story to story is permitted.
- Mixing intermittent bracing methods from braced-wall line to braced-wall line is
permitted.
- Mixing intermittent bracing methods within a single braced-wall line is permitted
for all buildings in SDC A and B and detached one- or two-family dwellings in SDC
C. The length of required bracing must be based on the highest amount required for
each of the methods used in the braced-wall line.
- Mixing continuous sheathing methods and intermittent methods within a single braced
wall line is not permitted (see R602.10.4).
-
Mixing continuous sheathing methods with intermittent methods from exterior braced
wall line to exterior braced-wall line is not permitted in SDC D0, D1, and D2 or
in Basic Winds Speeds greater than 100 mph. This is permitted in other regions (see
R602.10.4).
Gypsum Wall Board on Inside
The required wind and seismic bracing amounts are based on braced wall panels with
gypsum wall board on the side of the wall opposite the bracing material. Some bracing
methods are exempted from this requirement, other methods are permitted to omit
the gypsum wall board with increases in bracing amounts up to 80%, and other methods
are permitted to omit the gypsum wall board without penalty (see Section R602.10.2.1).
This calculator evaluates parameters entered such as bracing method and allows the
user to enter yes or no only when permitted. The effect of omitting gypsum wall
board is shown as the "Gypsum on Inside Factor" in the Wind and Seismic
calculation summary.
Gypsum Board (GB) Construction Type
The required wind and seismic bracing amounts for Method GB bracing are based on
double-sided gypsum wall board. Single-sided gypsum wall board doubles the required
bracing amounts (see Table R602.10.1.2(1) footnote g for wind, and Section R602.10.3
for seismic).
Gypsum wall board panels installed horizontally will not require blocking of horizontal
joints (see Section R602.10.8) excepted as noted below.
The required wind bracing amount for Method GB may be reduced by 30% when double-sided
GB is installed with blocked horizontal joints and fastened at 4 inches on center
at all panel edges (see Table R602.10.1.2(1) footnote g).
Horizontal Joints Blocked
Bracing methods that use sheathing panels must have blocking behind all horizontal
joints. Some bracing methods permit the blocking to be omitted when the wind and
seismic bracing amounts are doubled; others permit blocking to be omitted without
penalty (see Section R602.10.8). This calculator allows the user to enter yes or
no only when omitting the blocking is permitted by the bracing method. The effect
of omitting blocking is shown as the "Blocked Joint Factor" in the Wind
and Seismic calculation summary.
Holdown Device Used
The required wind bracing amount may be reduced by 20% for some methods when an
800-pound holdown device is used on the end studs of each braced-wall panel in the
braced-wall line (see Table R602.10.1.2(1) footnote i).
Stone or masonry veneer exceeding the first-story height in higher SDC regions requires
wood structural panel sheathing and holdowns installed in accordance with Section
R602.12.1.3 and is indicated in this calculator as method BV-WSP. When method BV-WSP
is required, "Holdown Device Used" defaults to "Yes."
Click to save a file containing this project's information, which can be imported back to this calculator at a later time.
Seismic Design Category
The seismic design category is a way of measuring the earthquake hazard in a given
region. Buildings are assigned a Seismic Design Category (SDC) in accordance with
their location on the
map shown in IRC Figure R301.2(2). Note the following:
- Buildings in SDC A & B are in the lowest seismic hazard regions and are exempt
from the seismic requirements of the IRC, as are detached one- and two-family dwellings
in SDC C (see Section R301.2.2). For buildings in these regions this calculator will determine wind bracing amounts only.
- Buildings located in SDC E are in the highest seismic hazard
regions and are not permitted to be designed using the IRC. The IRC and this calculator
will not evaluate buildings in SDC E (see Section R301.2.2.4).
- The U.S. Geological Survey (USGS) offers a calculation
tool to help determine the appropriate Seismic Design Category based on the project
site zip code or longitude and latitude. Go to the USGS website at Design Ground Motions (usgs.gov)
for more information.
- Contact the local building department to confirm the Seismic
Design Category.
Basic Wind Speed
The Basic Wind Speed is a design parameter that represents a home's potential exposure to
high winds, as determined by its location on the map in IRC Figure R301.2(4)A. Note the following:
- This calculator evaluates the wind speeds included in IRC Table R602.10.3.1: 85 mph–110 mph.
- Buildings located in regions where the basic wind
speed equals or exceeds 110 mph from Figure R301.2(4)A or where wind design is
required in accordance with Figure R301.2(4)B may not use the bracing provisions
of the IRC (see Section R301.2.1.1).
- Contact the local building department to confirm the Basic Wind Speed.
Basic Wind Speed map
Click for larger version
Wind Exposure Category
The Wind Exposure Category reflects the characteristics of the ground surface surrounding the home. If the home is surrounded by several similar-sized objects, then the wind won't affect it as much as it would if the home were out in the open. The IRC defines the following exposure categories (see Section R301.2.1.4):
- Exposure B: Urban and suburban areas, wooded areas, or other terrain with numerous closely spaced obstructions having the size of single-family dwellings or larger. Exposure B shall be assumed unless the site meets the definition of another type exposure. The wind bracing amounts tabulated in the IRC are based on Exposure B.
- Exposure C: Open terrain with scattered obstructions, including surface undulations or other irregularities, having heights generally less than 30 feet extending more than 1,500 feet from the building site in any quadrant. This exposure shall also apply to any building located within Exposure B- type terrain where the building is directly adjacent to open areas of Exposure C-type terrain in any quadrant for a distance of more than 600 feet. This category includes flat open country
and grasslands. Bracing in Exposure C buildings will increase 20-40% over
Exposure B amounts.
- Exposure D: Flat, unobstructed areas exposed to wind flowing over open water
for a distance of at least 1 mile. Shorelines in Exposure D include inland
waterways, the Great Lakes and coastal areas of California, Oregon, Washington
and Alaska. This exposure shall apply only to those buildings and other
structures exposed to the wind coming from over the water. Exposure D extends
inland from the shoreline a distance of 1,500 feet or 10 times the height of the
building or structure, whichever is greater. Buildings in Exposure D will have a
50-70% increase in bracing over Exposure B amounts.
- Contact the local building department with questions about which exposure to assume.
Number of Parallel Braced-Wall Lines
A minimum of two braced-wall lines are required in a given
direction. Additional braced-wall lines will reduce the spacing between
braced-wall lines thereby
reducing the tabulated wind bracing amounts on each wall line. To compensate, an adjustment factor
must be applied to ensure the total amount of bracing in each direction is about
the same for a given structure regardless of the number of braced-wall lines (see
Table R602.10.3(2)). The seismic bracing amounts are not affected by
the number of parallel braced-wall lines.
Braced Wall Line Spacing “Average” Option
The 2012 IRC does not specify how to determine the spacing associated with a Braced Wall Line that
has parallel braced wall lines on both sides. In reference to the figure shown here, some jurisdictions
may require the spacing associated with BWL B to be the greater of the distance between A & B and B & C (34-ft).
This matches the requirements in the 2009 IRC but is conservative for most cases. Some jurisdictions may permit
the spacing associated with BWL B to be the average distance between A & B and B & C (28-ft), which typically
results in a lower amount of required bracing.
Supporting Stone or Masonry Veneer
Section R602.10.6.5 of the IRC requires method BV-WSP on “exterior braced wall lines and braced wall lines on the interior
of the building, backing or perpendicular to and laterally supporting veneered walls” when the stone or masonry veneer exceeds
the first-story height of detached one-or two-family dwellings in SDC D0, D1, or D2. In reference to the figure shown here,
Method BV-WSP must be used on BWLs 1, A, B, and C.
Braced wall line Location
The required wind and seismic bracing amounts in the IRC are increased as the number
of stories above the braced-wall line is increased (see Tables R602.10.1.3(1) and
R602.10.1.3(3)).
In some cases the number of stories above the braced-wall lines will be different
for braced-wall lines within the same story. One example would be a single-story
attached garage that is fully outside the perimeter of a two-story residence.
Eave-to-Ridge Height
Height measured from the top of the wall to the top of the roof ridge. The tabulated wind
bracing amounts in the IRC are based on a height of 10 feet. Increasing or decreasing
the height will increase or decrease the wind bracing amounts by as much as
+60% to -30% (see Table R602.10.3(2)). The seismic bracing amounts are not
affected by the eave-to-ridge height.
Stone or Masonry Veneer Exceeding 1st Story Height
In some cases, stone or masonry veneer that exceeds the 1st story level will increase
the required amount of seismic bracing and/or add new bracing requirements (see Section
R602.10.6.5). Wind bracing amounts are not affected by stone or masonry veneer. See
Section R703.7 for additional information on stone and masonry veneer.
Wall Dead Load
The tabulated seismic bracing amounts in the IRC are based on a 15 psf wall dead
load. Dead loads of 8 psf or less will decrease the required seismic bracing amounts
by 15% (see Table R602.10.3(4)). See Section R301.4 for determining dead loads.
A typical wood-stud partition wall with 1/2-inch gypsum board on both sides has
an estimated dead load of 8 psf. A typical exterior wood-stud wall has an estimated
dead load greater than 8 psf. See ASCE 7-05 standard and commentary for additional
information.
Wind bracing amounts are not affected by wall dead load.
Roof/Ceiling Dead Load
The tabulated seismic bracing amounts in the IRC are based on a 15 psf Roof/Ceiling Dead Load.
Larger dead loads will increase the required seismic bracing amounts up to 20% (see Table R602.10.3(4)). See Section R301.4 for determining dead loads.
A typical asphalt shingle roof/ceiling assembly has an estimated dead load of 15
psf or less. Heavier roof coverings such as clay or concrete tile may result in
a roof/ceiling dead load greater than 15 psf. See ASCE 7-05 standard and commentary
for additional information.
Wind bracing amounts are not affected by roof/ceiling dead load.
Braced wall line Spacing
The distance between adjacent, parallel braced-wall lines. The spacing for braced
wall lines that have parallel braced-wall lines on both sides is the greater of
the distance between each braced-wall line (see Figure R602.10.1.1).
This calculator assumes all parallel braced wall lines run continuously through the structure and uses the spacing between consecutively numbered braced wall lines in determining the bracing amount required.
If your project uses braced wall lines that stop midway through the structure or are located adjacent to non-consecutively numbered braced wall lines (as shown in IRC Figure R602.10.1.1),
you will need to modify the spacing inputs accordingly before entering them into the application.
The maximum braced wall line spacing for all buildings in SDC A and B and detached
one- or two-family dwellings in SDC C is 60 feet and the
maximum spacing for townhouses in SDC C is 50 feet (see Table R602.10.1.3). The
maximum spacing for all buildings in SDC D0, D1, and D2 is 25 feet with an exception
that permits a single spacing up to 35 feet (see Table R602.10.1.3).
This calculator evaluates the parameters entered and limits the maximum spacing
to 60, 50, or 35 feet on center and adjusts bracing amounts accordingly. For buildings
in SDC D0, D1, and D2 the user must ensure Braced Wall Line Spacing greater than
25 feet is acceptable.
Braced wall line Length
The length of a braced wall
line is the distance between the ends of the braced-wall line. The end of a braced wall
line is either : a) the intersection
with perpendicular exterior walls or b) the intersection with perpendicular or
angled braced
wall lines (see Section R602.10.1.1).
The longer a braced-wall line, the more mass that wall line must support. Seismic
bracing amounts are increased linearly as braced-wall line length is increased.
Wind bracing amounts are not affected by braced-wall line length.
Wall Height
Wall height shall be the vertical distance from the lower edge of the bottom plate to the upper edge of the upper top plate.
As wall height is increased the wind surface area increases and the mass of the
wall increases. The tabulated wind and seismic bracing amounts are based on a wall
height of 10 feet. Shorter wall heights will reduce the required amount of wind
bracing by up to 10%. Taller wall heights will increase the required amount of wind
and seismic bracing by up to 20%. See Section R301.3, Tables R602.10.3(2) and R602.10.3(4) for more information.
Bracing Method
The building codes define various construction methods that may be used to build
a code-compliant braced wall panel:
The required amount of wind and seismic bracing is dependent on the method of wall
bracing used. Generally, methods LIB (let-in-bracing) and GB (gypsum board) are
considered the weakest, method CS (continuous sheathing) is considered the strongest,
and the other methods are in between.
Twelve intermittent methods and four continuous sheathing methods are described in Table R602.10.4.
Stone or masonry
veneer exceeding the 1st story height in higher SDC regions requires wood structural
panel sheathing and holdowns installed in accordance with Section R602.10.6.5 and
is indicated in this calculator as method BV-WSP.
When mixing bracing methods, the user must ensure the following limits are satisfied
(see Section R602.10.4.1):
- Mixing intermittent and continuous sheathing bracing methods from story to story is permitted.
- Mixing intermittent bracing methods from braced-wall line to braced-wall line within a story is permitted.
Within Seismic Design Categories A, B and C or in regions where the basic wind speed is less than or
equal to 100 mph, mixing of intermittent bracing and continuous sheathing methods from braced wall line
to braced wall line within a story shall be permitted.
- Mixing intermittent bracing methods along a braced-wall line is permitted
for all buildings in SDC A and B and dwellings in SDC
C provided the length of required bracing in accordance with Table R602.10.3(1) or R602.10.3(3)
is the highest value of all intermittent bracing methods used.
- Mixing continuous sheathing methods CS-WSP, CS-G and CS-PF along a braced wall line shall be permitted.
- Mixing continuous sheathing methods with intermittent methods from exterior braced
wall line to exterior braced-wall line is not permitted in SDC D0, D1, and D2 or
in Basic Winds Speeds greater than 100 mph. This is permitted in other regions (see
R602.10.4).
- In Seismic Design Categories A and B, and for detached one- and two- family dwellings in Seismic Design Category C,
mixing of intermittent bracing methods along the interior portion of a braced wall line with continuous sheathing
methods CS-WSP, CS-G and CS-PF along the exterior portion of the same braced wall line shall be permitted.
The length of required bracing shall be the highest value of all intermittent bracing methods used in accordance with
Table R602.10.3(1) or R602.10.3(3) as adjusted by Tables R602.10.3(2) and R602.10.3(4), respectively.
The requirements of Section R602.10.7 shall apply to each end of the continuously sheathed portion of the
braced wall line.
Gypsum Wall Board on Inside
The required wind and seismic bracing amounts are based on braced wall panels with
gypsum wall board on the side of the wall opposite the bracing material. Some bracing
methods are exempted from this requirement, other methods are permitted to omit
the gypsum wall board with increases in bracing amounts up to 50%, and other methods
are permitted to omit the gypsum wall board without penalty (see Tables R602.10.3(2) and R602.10.3(4)).
This calculator evaluates parameters entered such as bracing method and allows the
user to enter yes or no only when permitted. The effect of omitting gypsum wall
board is shown as the "Gypsum on Inside Factor" in the Wind and Seismic calculation
summary.
Gypsum Board (GB) Construction Type
The required wind and seismic bracing amounts for Method GB bracing are based on
double-sided gypsum wall board. Single-sided gypsum wall board doubles the required
bracing amounts (see Table R602.10.5).
Gypsum wall board panels installed horizontally will not require blocking of horizontal
joints (see Section R602.10.10) excepted as noted below.
The required wind bracing amount for Method GB may be reduced by 30% when double-sided GB is installed with blocked horizontal joints and fastened at 4 inches on
center at all panel edges (see Table R602.10.3(2)).
Horizontal Joints Blocked
Bracing methods that use sheathing panels must have blocking behind all horizontal
joints. Some bracing methods permit the blocking to be omitted when the wind and
seismic bracing amounts are doubled, others permit blocking to be omitted without
penalty (see Section R602.10.10). This calculator allows the user to enter yes or
no only when omitting the blocking is permitted by the bracing method. The effect of omitting blocking is shown as the "Blocked
Joint Factor" in the Wind and Seismic calculation summary.
Holdown Device Used
The required wind bracing amount may be reduced by 20% for some methods when an
800-pound holdown device is used on the end studs of each braced-wall panel in
the braced-wall line (see Table R602.10.3(2)).
Stone or masonry veneer exceeding the first-story height in higher SDC regions requires
wood structural panel sheathing and holdowns installed in accordance with Section
R602.10.6.5 and is indicated in this calculator as method BV-WSP. When method BV-WSP
is required, "Holdown Device Used" defaults to "Yes."
Seismic Design Category
The seismic design category is a way of measuring the earthquake hazard in a given
region. Buildings are assigned a Seismic Design Category (SDC) in accordance with
their location on the
map shown in IRC Figure R301.2(2). Note the following:
- Buildings in SDC A & B are in the lowest seismic hazard regions and are exempt
from the seismic requirements of the IRC, as are detached one- and two-family dwellings
in SDC C (see Section R301.2.2). For buildings in these regions this calculator will determine wind bracing amounts only.
- Buildings located in SDC E are in the highest seismic hazard
regions and are not permitted to be designed using the IRC. The IRC and this calculator
will not evaluate buildings in SDC E (see Section R301.2.2.4).
- The U.S. Geological Survey (USGS) offers a calculation
tool to help determine the appropriate Seismic Design Category based on the project
site zip code or longitude and latitude. Go to the USGS website at Design Ground Motions (usgs.gov)
for more information.
- Contact the local building department to confirm the Seismic
Design Category.
Ultimate Design Wind Speed
The Ultimate Design Wind Speed is a design parameter that represents a home's potential exposure to
high winds, as determined by its location on the map in IRC Figure R301.2(4)A. Note the following:
- This calculator evaluates the wind speeds included in IRC Table R602.10.3.1: 110 mph–140 mph.
- Buildings located in regions where the ultimate design wind speed equals or exceeds 140 mph from Figure R301.2(4)A or where wind design is
required in accordance with Figure R301.2(4)B
may not use the bracing provisions of the IRC (see Section R301.2.1.1).
- Contact the local building department to confirm the Ultimate Design Wind Speed.
Ultimate Design Wind Speed map
Click for larger version
Wind Exposure Category
The Wind Exposure Category reflects the characteristics of the ground surface surrounding the home. If the home is surrounded by several similar-sized objects, then the wind won't affect it as much as it would if the home were out in the open. The IRC defines the following exposure categories (see Section R301.2.1.4):
- Exposure B: Urban and suburban areas, wooded areas, or other terrain with numerous closely spaced obstructions having the size of single-family dwellings or larger. Exposure B shall be assumed unless the site meets the definition of another type exposure. The wind bracing amounts tabulated in the IRC are based on Exposure B.
-
Exposure C: Open terrain with scattered obstructions, including surface undulations or other irregularities, having heights generally less than
30 feet extending more than 1,500 feet from the building site in any quadrant. This exposure shall also apply to any building located within Exposure
B type terrain where the building is directly adjacent to open areas of Exposure C type terrain in any quadrant for a distance of more than 600 feet.
This category includes flat, open country and grasslands. Bracing in Exposure C buildings will increase 20-40% over Exposure B amounts.
-
Exposure D: Flat, unobstructed areas exposed to wind flowing over open water,
smooth mud flats, salt flats and unbroken ice for a distance of not less than 5,000 feet.
This exposure shall apply only to those buildings and other structures exposed to the wind coming
from over the unobstructed area. Exposure D extends downwind from the edge of the unobstructed area a
distance of 600 feet or 20 times the height of the building or structure, whichever is greater.
Buildings in Exposure D will have a 50-70% increase in bracing over Exposure B amounts.
- Contact the local building department with questions about which exposure to assume.
Stone or Masonry Veneer Exceeding 1st Story Height
In some cases, stone or masonry veneer that exceeds the 1st story level will increase the required
amount of seismic bracing and/or add new bracing requirements (see Section R602.10.6.5). Wind bracing
amounts are not affected by stone or masonry veneer. See Section R703.7 for additional information on stone and masonry veneer.
Number of Parallel Braced-Wall Lines
A minimum of two braced-wall lines are required in a given direction.
Additional braced-wall lines will reduce the spacing between braced-wall
lines thereby reducing the tabulated wind bracing amounts on each wall line.
To compensate, an adjustment factor must be applied to ensure the total amount
of bracing in each direction is about the same for a given structure regardless of
the number of braced-wall lines (see Table R602.10.3(2)).
The seismic bracing amounts are not affected by the number of parallel braced-wall lines.
Braced wall line Spacing
The distance between adjacent, parallel braced-wall lines.
The spacing for braced wall lines that have parallel braced-wall lines
on both sides is the greater of the distance between each braced-wall line (see Figure R602.10.1.1).
This calculator assumes all parallel braced wall lines run continuously through the structure and uses the spacing between consecutively numbered braced wall lines in determining the bracing amount required.
If your project uses braced wall lines that stop midway through the structure or are located adjacent to non-consecutively numbered braced wall lines (as shown in IRC Figure R602.10.1.1),
you will need to modify the spacing inputs accordingly before entering them into the application.
The maximum braced wall line spacing for all buildings in SDC A and B and detached one- or two-family
dwellings in SDC C is 60 feet and the maximum spacing for townhouses in SDC C is 50 feet (see Table R602.10.1.3).
The maximum spacing for all buildings in SDC D0, D1, and D2 is 25 feet with an exception that permits a single spacing up to 35 feet (see Table R602.10.1.3).
This calculator evaluates the parameters entered and limits the maximum spacing to 60, 50, or 35
feet on center and adjusts bracing amounts accordingly. For buildings in SDC D0, D1, and D2
the user must ensure Braced Wall Line Spacing greater than 25 feet is acceptable.
Braced Wall Line Spacing "Average" Option
The 2021 IRC includes two options to determine the spacing associated with a Braced Wall Line
that has parallel braced wall lines on both sides. In reference to the figure shown here,
the spacing associated with BWL B may be taken as the greater of the distance between A & B and B & C (34-ft).
Alternatively, the spacing associated with BWL B may be taken as the average distance between A & B and B & C
(28-ft), which typically results in a lower amount of required bracing (see Table R602.10.3(1) Footnote c).
This calculator assumes all parallel braced wall lines run continuously through the structure and uses the spacing between consecutively numbered braced wall lines in determining the bracing amount required.
If your project uses braced wall lines that stop midway through the structure or are located adjacent to non-consecutively numbered braced wall lines (as shown in IRC Figure R602.10.1.1),
you will need to modify the spacing inputs accordingly before entering them into the application.
Braced wall line Location
The required wind and seismic bracing amounts in the IRC are increased as the number
of stories above the braced-wall line is increased (see Tables R602.10.3(1) and R602.10.3(3)).
In some cases the number of stories above the braced-wall lines will be different for braced-wall
lines within the same story. One example would be a single-story attached garage that is fully
outside the perimeter of a two-story residence.
Eave-to-Ridge Height
Height measured from the top of the wall to the top of the roof ridge. The tabulated wind bracing amounts in the
IRC are based on a height of 10 feet. Increasing or decreasing the height will increase or decrease the wind bracing
amounts by as much as +60% to -30% (see Table R602.10.3(2)). The seismic bracing amounts are not affected by the eave-to-ridge height.
Wall Height
Wall height shall be the vertical distance from the lower edge of the bottom plate to the upper edge of the upper top plate (see R602.10.3.1).
As wall height is increased the wind surface area increases and the mass of the wall increases.
The tabulated wind and seismic bracing amounts are based on a wall height of 10 feet. Shorter wall
heights will reduce the required amount of wind bracing by up to 10%. Taller wall heights will increase
the required amount of wind and seismic bracing by up to 20%. See Section R301.3, Tables R602.10.3(2) and
R602.10.3(4) for more information.
Bracing Method
The building codes define various construction methods that may be used to build
a code-compliant braced wall panel:
The required amount of wind and seismic bracing is dependent on the method of wall bracing used.
Generally, methods LIB (let-in-bracing) and GB (gypsum board) are considered the weakest, method
CS (continuous sheathing) is considered the strongest, and the other methods are in between.
Twelve intermittent methods and four continuous sheathing methods are described in Table R602.10.4.
Stone or masonry veneer exceeding the 1st story height in higher SDC regions requires wood structural
panel sheathing and holdowns installed in accordance with Section R602.10.6.5 and is
indicated in this calculator as method BV-WSP.
When mixing bracing methods, the user must ensure the following limits are satisfied (see Section R602.10.4.1):
- Mixing intermittent and continuous sheathing bracing methods from story to story is permitted.
- Mixing intermittent bracing methods from braced-wall line to braced-wall line within a story is permitted.
Within Seismic Design Categories A, B and C or in regions where the ultimate design wind speed is less than or
equal to 130 mph, mixing of intermittent bracing and continuous sheathing methods from braced wall line to braced
wall line within a story shall be permitted.
- Mixing intermittent bracing methods along a braced-wall line is permitted for all buildings in SDC A and B
and detached dwellings in SDC C provided the length of required bracing in accordance with Table R602.10.3(1) or
R602.10.3(3) is the highest value of all intermittent bracing methods used.
- Mixing continuous sheathing methods CS-WSP, CS-G and CS-PF along a braced wall line shall be permitted.
Intermittent methods ABW, PFH and PFG shall be permitted to be used along a braced-wall line with continuous sheathed methods.
- Mixing continuous sheathing methods with intermittent methods from exterior braced wall line to exterior braced-wall line is
not permitted in SDC D0, D1, and D2 or when ultimate design wind speed exceeds 130 mph.
This is permitted in other regions (see R602.10.4).
- In Seismic Design Categories A and B, and for detached one- and two- family dwellings in Seismic Design Category C,
mixing of intermittent bracing methods along the interior portion of a braced wall line with continuous sheathing methods CS-WSP,
CS-G and CS-PF along the exterior portion of the same braced wall line shall be permitted. The length of required bracing shall
be the highest value of all intermittent bracing methods used in accordance with Table R602.10.3(1) or R602.10.3(3) as adjusted
by Tables R602.10.3(2) and R602.10.3(4), respectively. The requirements of Section R602.10.7 shall apply to each end of the
continuously sheathed portion of the braced wall line.
Gypsum Wall Board on Inside
The required wind and seismic bracing amounts are based on braced wall panels with
gypsum wall board on the side of the wall opposite the bracing material. Some bracing methods
are exempted from this requirement, other methods are permitted to omit the gypsum wall board
with increases in bracing amounts up to 50%, and other methods are permitted to omit the
gypsum wall board without penalty (see Tables R602.10.3(2) and R602.10.3(4)).
This calculator evaluates parameters entered such as bracing method and allows the user to
enter yes or no only when permitted. The effect of omitting gypsum wall board is shown as
the "Gypsum on Inside Factor" in the Wind and Seismic calculation summary
Gypsum Board (GB) Construction Type
The required wind and seismic bracing amounts for Method GB bracing are based on double-sided gypsum wall board.
Single-sided gypsum wall board doubles the required bracing amounts (see Table R602.10.5).
Gypsum wall board panels installed horizontally will not require blocking of horizontal joints (see Section R602.10.10) excepted as noted below.
The required wind bracing amount for Method GB may be reduced by 30% when double-sided GB is installed with blocked horizontal joints and
fastened at 4 inches on center at all panel edges (see Table R602.10.3(2)).
Horizontal Joints Blocked
Bracing methods that use sheathing panels must have blocking behind all horizontal joints.
Some bracing methods permit the blocking to be omitted when the wind and seismic bracing amounts are doubled,
others permit blocking to be omitted without penalty (see Section R602.10.10). This calculator allows the user
to enter yes or no only when omitting the blocking is permitted by the bracing method. The effect of omitting
blocking is shown as the "Blocked Joint Factor" in the Wind and Seismic calculation summary.
Horizontal Joints Blocked
Bracing methods that use sheathing panels must have blocking behind all horizontal joints. Bracing methods WSP and CS-WSP permit the blocking to be omitted when the wind and seismic bracing amounts are doubled; methods SFB, PBS, HPS and CS-SFB require the horizontal joints to be blocked in all cases (see Section R602.10.4.4). This calculator allows the user to enter yes or no only when omitting the blocking is permitted by the bracing method. The effect of omitting blocking is shown as the "Blocked Joint Factor" in the Wind and Seismic calculation summary.
Horizontal Joints Blocked
Bracing methods that use sheathing panels must have blocking behind all horizontal joints. Bracing methods WSP, CSP-WSP and PBS permit the blocking to be omitted when the wind and seismic bracing amounts are doubled; methods SFB, HPS and CS-SFB require the horizontal joints to be blocked in all cases (see Section R602.10.4.4). This calculator allows the user to enter yes or no only when omitting the blocking is permitted by the bracing method. The effect of omitting blocking is shown as the "Blocked Joint Factor" in the Wind and Seismic calculation summary.
Holdown Device Used
The required wind bracing amount may be reduced by 20% for some methods when an 800-pound holdown device is
used on the end studs of each braced-wall panel in the braced-wall line (see Table R602.10.3(2)).
Stone or masonry veneer exceeding the first-story height in higher SDC regions requires
wood structural panel sheathing and holdowns installed in accordance with Section R602.10.6.5
and is indicated in this calculator as method BV-WSP. When method BV-WSP is required, "Holdown Device Used" defaults to "Yes."
Supporting Stone or Masonry Veneer
Section R602.10.6.5 of the IRC requires method BV-WSP on "exterior braced wall lines and braced wall lines
on the interior of the building, backing or perpendicular to and laterally supporting veneered walls"
when the stone or masonry veneer exceeds the first-story height of detached one-or two-family dwellings in
SDC D0, D1, or D2. In reference to the figure shown here, Method BV-WSP must be used on BWLs 1, A, B, and C.
Wall Dead Load
The tabulated seismic bracing amounts in the IRC are based on a 15 psf wall dead load.
Dead loads of 8 psf or less will decrease the required seismic bracing amounts by 15%
(see Table R602.10.3(4)). See Section R301.4 for determining dead loads.
A typical wood-stud partition wall with 1/2-inch gypsum board on both sides has an estimated dead load of 8 psf.
A typical exterior wood-stud wall has an estimated dead load greater than 8 psf.
See ASCE 7-10 standard and commentary for additional information.
Wind bracing amounts are not affected by wall dead load.
Roof/Ceiling Dead Load
The tabulated seismic bracing amounts in the IRC are based on a 15 psf Roof/Ceiling Dead Load. Larger dead loads will increase
the required seismic bracing amounts up to 20% (see Table R602.10.3(4)). See Section R301.4 for determining dead loads.
A typical asphalt shingle roof/ceiling assembly has an estimated dead load of 15 psf or less.
Heavier roof coverings such as clay or concrete tile may result in a roof/ceiling dead load greater than 15 psf.
See ASCE 7-16 standard and commentary for additional information.
Wind bracing amounts are not affected by roof/ceiling dead load.
Braced wall line Length
The length of a braced wall line is the distance between the ends of the braced-wall line.
The end of a braced wall line is either : a) the intersection with perpendicular exterior walls or b)
the intersection with perpendicular or angled braced wall lines (see Section R602.10.1.1).
The longer a braced-wall line, the more mass that wall line must support. Seismic bracing amounts
are increased linearly as braced-wall line length is increased.
Wind bracing amounts are not affected by braced-wall line length.
Seismic Design Category
The seismic design category is a way of measuring the earthquake hazard in a given
region. Buildings are assigned a Seismic Design Category (SDC) in accordance with
their location on the map shown in IRC Figure R301.2(2). Note the following:
- Buildings in SDC A & B are in the lowest seismic hazard regions and are exempt
from the seismic requirements of the IRC, as are detached one- and two-family dwellings
in SDC C (see Section R301.2.2). For buildings in these regions this calculator will determine wind bracing amounts only.
- Buildings located in SDC E are in the highest seismic hazard
regions and are not permitted to be designed using the IRC. The IRC and this calculator
will not evaluate buildings in SDC E (see Section R301.2.2).
- Contact the local building department to confirm the Seismic
Design Category.
Ultimate Design Wind Speed
The Ultimate Design Wind Speed is a design parameter that represents a home's potential exposure to
high winds, as determined by its location on the map in IRC Figure R301.2(5)A. Note the following:
- This calculator evaluates the wind speeds included in IRC Table R602.10.3(1) 110 mph–140 mph.
- Buildings located in regions where the ultimate design wind speed equals or exceeds 140 mph from Figure R301.2(5)A or where wind design is
required in accordance with Figure R301.2(5)B
may not use the bracing provisions of the IRC (see Section R301.2.1.1).
- Contact the local building department to confirm the Ultimate Design Wind Speed.
Ultimate Design Wind Speed map
Click for larger version
Bracing Method
The building codes define various construction methods that may be used to build
a code-compliant braced wall panel:
- Let-In Bracing (LIB)
- Diagonal Wood Board (DWB)
- Wood-Structural-Panel Sheathing (WSP)
- Gypsum Board (GB)
- Structural Fiberboard Sheathing (SFB)
- Particleboard Sheathing (PBS)
- Portland Cement Plaster (PCP)
- Hardboard Panel Siding (HPS)
- Continuously sheathed wood structural panel (CS-WSP)
- Continuously Sheathed (CS)
- Alternate Braced Wall (ABW)
- Wood Structural Panels with Stone or Masonry Veneer (BV-WSP)
- Continuously sheathed structural fiberboard (CS-SFB)
The required amount of wind and seismic bracing is dependent on the method of wall bracing used.
Generally, methods LIB (let-in-bracing) and GB (gypsum board) are considered the weakest, method
CS (continuous sheathing) is considered the strongest, and the other methods are in between.
Twelve intermittent methods and four continuous sheathing methods are described in Table R602.10.4.
Stone or masonry veneer exceeding the 1st story height in higher SDC regions requires wood structural
panel sheathing and holdowns installed in accordance with Section R602.10.6.5 and is
indicated in this calculator as method BV-WSP.
When mixing bracing methods, the user must ensure the following limits are satisfied (see Section R602.10.4.1):
- Mixing intermittent and continuous sheathing bracing methods from story to story is permitted.
- Mixing intermittent bracing methods from braced-wall line to braced-wall line within a story is permitted.
Within Seismic Design Categories A, B and C or in regions where the ultimate design wind speed is less than or
equal to 130 mph, mixing of intermittent bracing and continuous sheathing methods from braced wall line to braced
wall line within a story shall be permitted.
- Mixing intermittent bracing methods along a braced-wall line is permitted for all buildings in SDC A and B
and detached dwellings in SDC C provided the length of required bracing in accordance with Table R602.10.3(1) or
R602.10.3(3) is the highest value of all intermittent bracing methods used.
- Mixing continuous sheathing methods CS-WSP, CS-G and CS-PF along a braced wall line shall be permitted.
Intermittent methods ABW, PFH and PFG shall be permitted to be used along a braced-wall line with continuous sheathed methods.
- Mixing continuous sheathing methods with intermittent methods from exterior braced wall line to exterior braced-wall line is
not permitted in SDC D0, D1, and D2 or when ultimate design wind speed exceeds 130 mph.
This is permitted in other regions (see R602.10.4).
- In Seismic Design Categories A and B, and for detached one- and two- family dwellings in Seismic Design Category C,
mixing of intermittent bracing methods along the interior portion of a braced wall line with continuous sheathing methods CS-WSP,
CS-G and CS-PF along the exterior portion of the same braced wall line shall be permitted. The length of required bracing shall
be the highest value of all intermittent bracing methods used in accordance with Table R602.10.3(1) or R602.10.3(3) as adjusted
by Tables R602.10.3(2) and R602.10.3(4), respectively. The requirements of Section R602.10.7 shall apply to each end of the
continuously sheathed portion of the braced wall line.
Stone or Masonry Veneer Exceeding 1st Story Height
In some cases, stone or masonry veneer that exceeds the 1st story level will increase the required
amount of seismic bracing and/or add new bracing requirements (see Section R602.10.6.5). Wind bracing
amounts are not affected by stone or masonry veneer. See Section R703.8 for additional information on stone and masonry veneer.
Wall Dead Load
The tabulated seismic bracing amounts in the IRC are based on a 15 psf wall dead load.
Dead loads of 8 psf or less will decrease the required seismic bracing amounts by 15%
(see Table R602.10.3(4)). See Section R301.4 for determining dead loads.
A typical wood-stud partition wall with 1/2-inch gypsum board on both sides has an estimated dead load of 8 psf.
A typical exterior wood-stud wall has an estimated dead load greater than 8 psf.
See ASCE 7-16 standard and commentary for additional information.
Wind bracing amounts are not affected by wall dead load.
Gypsum Board (GB) Construction Type
The required wind and seismic bracing amounts for Method GB bracing are based on double-sided gypsum wall board.
Single-sided gypsum wall board doubles the required bracing amounts (see Table R602.10.5).
Gypsum wall board panels installed horizontally will not require blocking of horizontal joints (see Section R602.10.4.4) except as noted below.
The required wind bracing amount for Method GB may be reduced by 30% when double-sided GB is installed with blocked horizontal joints and
fastened at 4 inches on center at all panel edges (see Table R602.10.3(2)).
Seismic Design Category
The seismic design category is a way of measuring the earthquake hazard in a given
region. Buildings are assigned a Seismic Design Category (SDC) in accordance with
their location on the map shown in IRC Figure R301.2.2.1(1) through R301.2.2.1(6). Note the following:
- Buildings in SDC A & B are in the lowest seismic hazard regions and are exempt
from the seismic requirements of the IRC, as are detached one- and two-family dwellings
in SDC C (see Section R301.2.2). For buildings in these regions this calculator will determine wind bracing amounts only.
- Buildings located in SDC E are in the highest seismic hazard
regions and are not permitted to be designed using the IRC. The IRC and this calculator
will not evaluate buildings in SDC E (see Section R301.2.2).
- Contact the local building department to confirm the Seismic
Design Category.
Ultimate Design Wind Speed
The Ultimate Design Wind Speed is a design parameter that represents a home's potential exposure to
high winds, as determined by its location on the map in IRC Figure R301.2(2). Note the following:
- This calculator evaluates the wind speeds included in IRC Table R602.10.3(1) 95 mph–140 mph.
- Buildings located in regions where the ultimate design wind speed equals or exceeds 140 mph from Figure R301.2(2) or where wind design is
required in accordance with Figure R301.2.1.1
may not use the bracing provisions of the IRC (see Section R301.2.1.1).
- Contact the local building department to confirm the Ultimate Design Wind Speed.
Ultimate Design Wind Speed map
Click for larger version
Bracing Method
The building codes define various construction methods that may be used to build
a code-compliant braced wall panel:
- Let-In Bracing (LIB)
- Diagonal Wood Board (DWB)
- Wood-Structural-Panel Sheathing (WSP)
- Gypsum Board (GB)
- Structural Fiberboard Sheathing (SFB)
- Particleboard Sheathing (PBS)
- Portland Cement Plaster (PCP)
- Hardboard Panel Siding (HPS)
- Continuously sheathed wood structural panel (CS-WSP)
- Continuously Sheathed (CS)
- Alternate Braced Wall (ABW)
- Portal Frame With Hold-downs (PFH)
- Portal Frame at Garage (PFG)
- Wood Structural Panels with Stone or Masonry Veneer (BV-WSP)
- Continuously sheathed structural fiberboard (CS-SFB)
The required amount of wind and seismic bracing is dependent on the method of wall bracing used.
Generally, methods LIB (let-in-bracing) and GB (gypsum board) are considered the weakest, method
CS (continuous sheathing) is considered the strongest, and the other methods are in between.
Twelve intermittent methods and four continuous sheathing methods are described in Table R602.10.4.
Stone or masonry veneer exceeding the 1st story height in higher SDC regions requires wood structural
panel sheathing and holdowns installed in accordance with Section R602.10.6.5 and is
indicated in this calculator as method BV-WSP.
When mixing bracing methods, the user must ensure the following limits are satisfied (see Section R602.10.4.1):
- Mixing intermittent and continuous sheathing bracing methods from story to story is permitted.
- Mixing intermittent bracing methods from braced-wall line to braced-wall line within a story is permitted.
Within Seismic Design Categories A, B and C or in regions where the ultimate design wind speed is less than or
equal to 130 mph, mixing of intermittent bracing and continuous sheathing methods from braced wall line to braced
wall line within a story shall be permitted.
- Mixing intermittent bracing methods along a braced-wall line is permitted for all buildings in SDC A and B
and detached dwellings in SDC C provided the length of required bracing in accordance with Table R602.10.3(1) or
R602.10.3(3) is the highest value of all intermittent bracing methods used.
- Mixing continuous sheathing methods CS-WSP, CS-G and CS-PF along a braced wall line shall be permitted.
Intermittent methods ABW, PFH and PFG shall be permitted to be used along a braced-wall line with continuous sheathed methods.
- Mixing continuous sheathing methods with intermittent methods from exterior braced wall line to exterior braced-wall line is
not permitted in SDC D0, D1, and D2 or when ultimate design wind speed exceeds 130 mph.
This is permitted in other regions (see R602.10.4).
- In Seismic Design Categories A and B, and for detached one- and two- family dwellings in Seismic Design Category C,
mixing of intermittent bracing methods along the interior portion of a braced wall line with continuous sheathing methods CS-WSP,
CS-G and CS-PF along the exterior portion of the same braced wall line shall be permitted. The length of required bracing shall
be the highest value of all intermittent bracing methods used in accordance with Table R602.10.3(1) or R602.10.3(3) as adjusted
by Tables R602.10.3(2) and R602.10.3(4), respectively. The requirements of Section R602.10.7 shall apply to each end of the
continuously sheathed portion of the braced wall line.
Stone or Masonry Veneer Exceeding 1st Story Height
In some cases, stone or masonry veneer that exceeds the 1st story level will increase the required
amount of seismic bracing and/or add new bracing requirements (see Section R602.10.6.5.2 and R602.10.6.5.3). Wind bracing
amounts are not affected by stone or masonry veneer. See Section R703.8 for additional information on stone and masonry veneer.
Ultimate Design Wind Speed
The Ultimate Design Wind Speed is a design parameter that represents a home's potential exposure to
high winds, as determined by its location on the map in IRC Figure R301.2(2). Note the following:
- This calculator evaluates the wind speeds included in IRC Table R602.10.3(1) 95 mph–140 mph.
- Buildings located in regions where the ultimate design wind speed equals or exceeds 140 mph from Figure R301.2(2) or where wind design is
required in accordance with Figure R301.2.1.1
may not use the bracing provisions of the IRC (see Section R301.2.1.1).
- Contact the local building department to confirm the Ultimate Design Wind Speed.
Ultimate Design Wind Speed map
Click for larger version