structural plan review wall bracing continued lesson 7 · structural plan review wall bracing...

Structural Plan Review

Wall Bracing Continued

Lesson 7

Updated: March 2017

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Braced Wall Connections

In order to be effective, braced wall panels must connect the roof diaphragm to

the foundation system. The provisions in R602.10.6 give minimum prescriptive

criteria for the connection of the BWPs to the double top plate and to the

foundation system.

R602.10.6 Braced wall panel connections. Braced wall panels shall

be connected to floor framing or foundations as follows:

1. Where joists are perpendicular to a braced wall panel above or

below, a rim joist, band joist or blocking shall be provided along the

entire length of the braced wall panel in accordance with Figure

R602.10.6(1). Fastening of top and bottom wall plates to framing, rim

joist, band joist and/or blocking shall be in accordance with Table

R602.3(1).

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Braced Wall Connections Cont.

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Braced wall connections cont. 2. Where joists are parallel to a braced wall panel above or below, a rim joist, end joist

or other parallel framing member shall be provided directly above and below the braced

wall panel in accordance with Figure R602.10.6(2). Where a parallel framing member is

not located directly above and below the panel, full-depth blocking at 16 inch (406 mm)

spacing shall be provided between the parallel framing members to each side of the

braced wall panel in accordance with Figure R602.10.6(2). Fastening of blocking and

wall plates shall be in accordance with Table R602.3(1) and Figure R602.10.6(2).

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Braced wall connections cont.

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3. Connections of braced wall panels to concrete or masonry shall be in accordance

with Section R403.1.8.

R403.1.8 Foundation anchorage. Sill plates and walls supported directly on continuous

foundations shall be anchored to the foundation in accordance with this section. Wood

sole plates at all exterior walls on monolithic slabs, wood sole plates of braced wall

panels at building interiors on monolithic slabs and all wood sill plates shall be anchored

to the foundation with anchor bolts spaced a maximum of 6 feet (1829 mm) on center.

Bolts shall be at least ½ inch (12.7 mm) in diameter and shall extend a minimum of 7

inches (178 mm) into concrete or grouted cells of concrete masonry units. A nut and

washer shall be tightened on each anchor bolt. There shall be a minimum of two bolts per

plate section with one bolt located not more than 12 inches (305 mm) or less than seven

bolt diameters from each end of the plate section. Interior bearing wall sole plates on

monolithic slab foundation that are not part of a braced wall panel shall be positively

anchored with approved fasteners. Sill plates and sole plates shall be protected against

decay and termites where required by Sections R317 and R318. Cold-formed steel

framing systems shall be fastened to wood sill plates or anchored directly to the

foundation as required in Section R505.3.1 or R603.3.1.

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7” 7

”

To prevent walls and floors from shifting

under lateral loads, the code requires

anchorage to the supporting foundation.

Anchor bolts installed as specified in this

section supply the minimum required

capacity. Figure R403.1.6 illustrates

anchorage of wood sill plates. The 1/2-

inch bolts must extend into concrete or

grouted cells of concrete masonry units.

This anchorage applies at exterior walls

in any seismic design category.

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R403.1.8.1 Foundation anchorage in Seismic Design Categories C,D1 andD2.

In addition to the requirements of Section R403.1.6, the following requirements shall

apply to wood light-frame structures in Seismic Design Categories D1 and D2 and wood

light-frame townhouses in Seismic Design Category C.

1. Plate washers conforming to Section R602.11.1 shall be provided for all anchor bolts

over the full length of required braced wall lines. Properly sized cut washers shall be

permitted for anchor bolts in wall lines not containing braced wall panels.

2. Not shown

3. Not shown

4. In Seismic Design Category D2, the

maximum anchor bolt spacing shall be

4 feet (1219 mm)for buildings over two

stories in height.

5. Not shown

6. Not shown

9

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R602.11 Wall anchorage. Braced wall line sills shall be anchored to concrete or masonry

foundations in accordance with Sections R403.1.6 and R602.11.1.

602.11.1 Wall anchorage for all buildings in Seismic Design Categories D1 and D2 and

townhouses in Seismic Design Category C. Plate washers, a minimum of 0.229 inch by 3

inches by 3 inches (5.8 mm by 76 mm by 76 mm) in size, shall be provided between the

foundation sill plate and the nut except where approved anchor straps are used. The hole in

the plate washer is permitted to be diagonally slotted with a width of up to 3/16 inch (5 mm)

larger than the bolt diameter and a slot length not to exceed 13/4 inches (44 mm), provided a

standard cut washer is placed between the plate washer and the nut.

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R602.10.6.1 Braced wall panel connections for Seismic Design Categories D1 and D2.

Braced wall panels shall be fastened to required foundations in accordance with Section

R602.11.1, and top plate lap splices shall be face-nailed with at least eight 16d nails on

each side of the splice.

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R602.10.6.2 Connections to roof framing. Exterior braced wall panels shall be

connected to roof framing as follows.

1. Parallel rafters or roof trusses shall be attached to the top plates of braced wall panels in

accordance with Table R602.3(1).

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2. For SDC A, B and C and wind speeds less than 100 miles per hour (45 m/s), where

the distance from the top of the rafters or roof trusses and perpendicular

top plates is 91/4 inches (235 mm) or less, the rafters or roof trusses shall be connected

to the top plates of braced wall lines in accordance with Table R602.3(1) and blocking

need not be installed. Where the distance from the top of the rafters and perpendicular

top plates is between 91/4 inches (235 mm) and 151/4 inches (387 mm) the rafters shall be

connected to the top plates of braced wall panels with blocking in accordance with

Figure R602.10.6.2(1) and attached in accordance with Table R602.3(1). Where the

distance from the top of the roof trusses and perpendicular top plates is between 91/4

inches (235 mm) and 151/4 inches (387 mm) the roof trusses shall be connected to the top

plates of braced wall panels with blocking in accordance with Table R602.3(1).

The following connection details represent a simple principle: braced wall

lines extend from diaphragm to diaphragm and must be connected at both top

and bottom.

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R602.10.1.2.1 Braced wall panel uplift load path. Braced wall panels located at

exterior walls that support roof rafters or trusses (including stories below top story) shall

have the framing members connected in accordance with one of the following:

1. Fastening in accordance with Table R602.3(1)

where:

1.1. The basic wind speed does not exceed 90 mph (40 m/s), the wind

exposure category is B, the roof pitch is 5:12 or greater, and the roof span is

32 feet (9754 mm) or less, or

1.2. The net uplift value at the top of a wall does not exceed 100 plf. The net

uplift value shall be determined in accordance with Section R802.11 and shall

be permitted to be reduced by 60 plf (86 N/mm) for each full wall above.

2. Where the net uplift value at the top of a wall exceeds 100 plf (146 N/mm), installing

approved uplift framing connectors to provide a continuous load path from the top of the

wall to the foundation. The net uplift value shall be as determined in Item 1.2 above.

3. Bracing and fasteners designed in accordance with accepted engineering practice to

resist combined uplift and shear forces.

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R802.11.1 Uplift resistance. Roof assemblies which are subject to wind uplift pressures

of 20 pounds per square foot (960 Pa) or greater as established in Table R301.2(2) shall

have rafter or truss ties provided at bearing locations in accordance with Table R802.11.

A continuous load path shall be designed to transmit the uplift forces from the rafter or

truss ties to the foundation.

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Braced wall panel uplift load path

From Section R602.10.1.2.1, Item 1.1, it can be inferred that the Table R602.3(1),

Item 5, prescriptive nailing requirements provide 100 pounds of net uplift (plf)

resistance to properly attached roofs. No additional attachment is required until the

uplift loads specified in Table R802.11 exceed this amount. In addition, Section

R602.10.1.2.1, Item 1.2, provides the effective weight of each full wall above the

wall-to-floor connection in question as 60 plf . This amount can be subtracted from

the uplift amount, as the uplift requirement for each lower floor is calculated (see

Example 1.2). Given this information, the user is able to use the truss or rafter

connection uplift force provided in Table R802.11 and its notes to compute the net

uplift requirement for a structure at a given location. Note that the notes of Table

R802.11 are important and must be considered.

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Uplift @ Brace Wall Panels

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R602.10.7 Braced wall panel support. Braced wall panel support shall be provided

as follows:

1. Cantilevered floor joists, supporting braced wall lines, shall comply with

Section R502.3.3. Cantilevered floor joists complying with Section R502.3.3

shall be permitted to support braced wall panels. In all structures in Seismic

Design Category D1 and D2 and in townhouses in Seismic Design Category C,

cantilevered floor joists supporting braced wall panels shall comply with the

requirements of Section R301.2.2.2.5, item 1. Solid blocking shall be provided

at the nearest bearing wall location. In Seismic Design Categories A, B and C,

where the cantilever is not more than 24 inches (610 mm), a full height rim joist

instead of solid blocking shall be provided.

2. Elevated post or pier foundations supporting braced wall panels shall be

designed in accordance with accepted engineering practice.

The above two items have been covered earlier in this module. Next we see

the provisions for when masonry stem walls are used as the base for brace

wall panels.

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3. Masonry stem walls with a length of 48 inches (1220 mm) or less supporting braced

wall panels shall be reinforced in accordance with Figure R602.10.7. Masonry stem

walls with a length greater than 48 inches (1220 mm) supporting braced wall panels

shall be constructed in accordance with Section R403.1. Braced wall panels constructed

in accordance with Sections R602.10.3.2 and R602.10.3.3 shall not be attached to

masonry stem walls (Portal Frames).

4. Concrete stem walls with a length of 48 inches (1219mm) or less, greater than 12

inches (305 mm) tall and less than 6 inches (152 mm) thick shall have reinforcement

sized and located in accordance with Figure R602.10.7.

5. In all structures in Seismic Design Category D1 and D2 and in townhouses in

Seismic Design Category C, the end of a braced wall panel over an opening in the wall

below are subject shall comply with the requirements of Section R301.2.2.2.5, item 3.

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R602.10.7 Braced wall panel support cont.

Figure R602.10.7

Masonry Stem Walls Supporting Braced Wall Panels

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R602.10.7 Braced wall panel support cont.

Figure R602.10.7

Masonry Stem Walls Supporting Braced Wall Panels

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Brace wall line spacing

Determining BWL spacing using Section 602.10.1.4 The provisions for brace wall line spacing between brace wall lines is covered

in the code Section 602.10.1.4 which states that the spacing shall be located in

accordance with Figure R602.10.1.4(1).

The braced wall spacing used in Tables 602.10.1.2(1 &2) is referring to the

spacing between lines A & B and the spacing

between lines B & C. If you are looking at the

table spacing for wall line A you would take

the distance between lines

A & B. If you are looking for

the table spacing for line B

then you would take the

greater distance

between lines A & B or

lines B & C.

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Brace wall line spacing cont.

Determining BWL spacing using Section 602.10.1.4 cont.

An example of the spacing for the box shaped building below would be:

Wall line A, L = 30’

Wall line B, L = 30’

Wall line 1, L = 60’

Wall line 2, L = 60’

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As seen in the example

on the right, Line A is

4’ perpendicular from each

wall that is parallel with

the wall line so the brace

wall line can use the gray

shaded walls for the wall

line bracing.

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The walls of the house are permitted to offset from the BWL:

• < or = 4’ on either side

of the BWL

• BWL is not required to

align with the actual wall(s)

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Brace wall spacing cont. The 12.5 foot end-distance provision is in place to prevent the elimination of a braced wall

panel in a wall line. For example, if the 12.5-foot rule is applied at each end of a 29-foot long

wall line, only a single panel is required in the wall line: one braced panel positioned 12.5 feet

from each end of the wall line12.5 feet + 4 feet + 12.5 feet = 29 feet. The provision eliminates

the possibility of such an interpretation. The bracing provisions require bracing at each end and

every 25 feet on center. A single panel in a braced wall line violates the intent of the provision to

have a minimum of two braced panels, and may not provide sufficient stability to the roof or

floor diaphragm above.

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Brace wall panel length along BWL

Once the wall line locations have been determined and that there are the

appropriate conforming panel configurations available then it must be verified

that the brace wall line has the minimum overall total length. In order to verify

this you move into the tables for the wind provisions (remember, we will look

at the seismic provisions and multi-story applications once we have the basic

understanding of the brace wall concept).

Table R602.10.1.2(1) is the table that establishes the basic minimum length for

brace wall panels based on brace wall type and spacing between wall lines.

Once the minimum length per the table is established then there are several

other tables that need to be referenced which have multipliers dependent

upon the variables of the particular building configuration. There are multipliers

for such things as exposure related to stories, roof ridge height, number of

braced wall lines and brace wall types.

Bracing requirements per the wind speed tables

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Brace wall panel length along BWL cont.

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Brace wall panel length along BWL cont. Determining BWP length using Table R602.10.1.2(1)

An example of the BW length for the box shaped building below would be:

Wall line A, spacing L = 60’

Per table using method WSP

(Wood Structural Panel)

Exposure B

Single story, 10 ft, wall height

Eave to ridge height = 15 ft.

No interior drywall

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The base wall line length for Wall Line A is 9.5 lineal feet of brace wall using

plywood structural panels. Now we need to check the multiplier tables:

This is a single story exposure B structure so the multiplier is 1.0

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The eave to ridge

height is 15 ft. for this

structure and the wall

height is 10 feet which

does not require a

multiplier per footnote “d”

but a 1.3 multiplier must

be used for the ridge

height. This multiplier

takes into account the

taller “sail” area.

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The building only has two resisting BWLs so an adjustment factor is not required.

Using the WSP method of bracing will require the BW length to be adjusted by

the 1.4 factor.

If the owner/designer chooses to install hold down devices per footnote ‘i’

then an adjustment factor of 0.8 can be used to reduce the BW length.

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Total required brace panel length @ Wall Line A:

Assuming the use of hold down devices @ panel ends

LA = (9.5)(1.0)(1.3)(1.4)(0.8) = 13.83’, use 14’

So using two panels, the length of each panel is 7’ within the 30’ long wall

Note: Due to the symmetry of the box configuration the same brace wall

configuration can be used for Line B.

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Brace wall length at Wall Lines 1 & 2:

For wall lines 1 & 2 we will assume that this is the gable end of the building

And as such there is the triangular portion of the roof structure facing the wind.

Wall lines 1 & 2, spacing L = 30’

Per table using method WSP (Wood Structural Panel)

Exposure B

Single story 10 ft., wall height

Eave to ridge height = 15 ft.

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The base wall line length for Wall Lines 1 & 2 for a 30 ft. BWL spacing is 5

lineal feet of brace wall using plywood structural panels. Again, we need to

check the multiplier tables:

This is a single story exposure B structure so the multiplier is 1.0

Using the WSP method of bracing will again require the BW length to be

adjusted by the 1.4 factor. This time we will not use the hold down provisions

from footnote ‘i’.

L1 & 2 = (9.5)(1.0)(1.3)(1.4) = 17.29’, use 20’

So using five panels, the length of each panel is 4’ within the 60’ long wall but

this exceeds the 25’ o.c. spacing would still be 5 – 4’ panels.

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Interpolation ORSC allows interpolation in many tables

No extrapolation

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Interpolation

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Interpolation cont.

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Interpolation cont.

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Interpolation cont.

Box Method

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Brace wall length analysis

8’

10’

6’-4”

9’

9’

Front Elevation

Left Side Elevation Roof Plan

Elevation and roof plan

for the example residence

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45’

15’

Determining brace wall lines at complex structures When looking at structures that do not have easily defined wall lines such as a

simple box it is helpful to consider the structure in a series of smaller boxes. By

approaching the structure in this fashion it will be easier to isolate individual brace

wall lines. As an example, wall line B is influenced by the box made up of wall

Lines 1 & 2 with wall lines A & B, also

the boxes made up of wall lines B & C

with wall lines 1 & 4 and Lines 3 & 4.

In regions controlled by wind and not

within Seismic Design Categories D1

& D2 the 45’ long spacing would be

allowed otherwise the maximum

spacing between wall lines is 25’ for

typical applications. Wall line 4 is

discontinuous but is influenced by

the boxes made up of wall lines B & C

with wall lines 1 & 4 and Lines 3 & 4

8’

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More brace wall length analysis cont.

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Wall Covering – Exterior

Key points:

• Section R703 outlines the requirements for exterior wall coverings.

• A general rule of thumb is that exterior wall coverings are installed in

accordance with the manufacturer’s installation instructions.

• Exterior walls of buildings must be protected against damage caused by

precipitation, wind and other weather conditions. This section also requires that

flashing be installed in the exterior wall at penetrations and terminations of the

exterior wall covering.

• R703.1.1 is the Oregon amendment of the “drainage plane” requirement.

• R703.2 is the water-resistive barrier (WRB) requirement.

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“The Drainage Plane”

R703.1.1 Exterior wall envelope.

• The exterior wall envelope shall be installed in a manner that water that enters

the assembly can drain to the exterior.

• The envelope shall consist of an exterior veneer, a water-resistive barrier as

required in Section R703.2, a minimum 1/8 inch (3 mm) space between the

water- resistive barrier and the exterior veneer, and integrated flashings as

required in Section R703.8.

• The required space shall be formed by the use of any non-corrodible furring

strip, drainage mat or drainage board.

• The envelope shall provide proper integration of flashings with the water-

resistive barrier, the space provided and the exterior veneer. These

components, in conjunction, shall provide a means of draining water that enters

the assembly to the exterior.

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Wall Covering – Exterior “The Drainage Plane”

R703.1.1 Exterior wall envelope. (Exceptions)

1. A space is not required where the exterior veneer is installed over a water-

resistive barrier complying with Section R703.2 that is manufactured in a

manner to enhance drainage and meets the 75-percent drainage efficiency

requirement of ASTM E2273 or other recognized national standards.

2. A space is not required where window sills are equipped with pan flashings that

drain to the exterior surface of the veneer in a through wall fashion. All pan

flashings shall be detailed within the construction documents and shall be of

either a self-adhering membrane complying with AAMA 711-07 or of an

approved corrosion-resistant material or a combination thereof. Self-adhering

membranes extending to the exterior surface of the veneer shall be concealed

with trims or other measures to protect from sunlight.

3. A space is not required for detached accessory structures.

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R703.1.1 Exterior wall envelope. (Exceptions continued)

4. A space is not required for additions, alterations or repairs where the new

exterior veneer is;

4.1. Matching the existing exterior veneer; and

4.2. Installed in the same plane as the existing veneer without a change

in direction or use of a control joint; and

4.3. Installed over a water-resistive barrier complying with Section

R703.2.

5. The requirements of Section R703.1 shall not be required over concrete or

masonry walls designed in accordance with Chapter 6 and flashed according

to Section R703.7 or R703.8.

6. Tested Exterior Envelope – See Section for details

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R703.2 Water-resistive barrier. One layer of No. 15 asphalt felt, free from holes

and breaks, complying with ASTMD226 for Type 1 felt or other approved water-

resistive barrier shall be applied over studs or sheathing of all exterior walls. Such

felt or material shall be applied horizontally, with the upper layer lapped over the

lower layer not less than 2 inches (51 mm). Where joints occur, felt shall be lapped

not less than 6 inches (152 mm). The felt or other approved material shall be

continuous to the top of walls and terminated at penetrations and building

appendages in a manner to meet the requirements of the exterior wall envelope as

described in Section R703.1.

Exception: Omission of the water-resistive barrier is permitted in the following

situations:

1. In detached accessory buildings.

2. Under exterior wall finish materials as permitted in Table R703.4.

3. Under paperbacked stucco lath when the paper backing is an approved water-

resistive barrier.

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“The Drainage Plane”

Part 1:

Drainage Plane R703.1.1

• 1/8” non-corrodible furring strips

• Drainage mat / wrap / board

+

Part 2:

Water Resistive Barrier

R703.2

• No. 15 ASTM D 226 Felt

• Other approved WRB

There are two parts that must be addressed to satisfy the

prescriptive requirements of ORSC Section R703.1 & R703.2:

Note: Application of certain exceptions from R703.1.1 essentially combine

parts 1 & 2 into a single step path.

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On the left, a section detail including non-corrodible furring strips

with No. 15 felt. On the right, a section detail satisfying both

R703.1.1 and R703.2 in a single step through the use of

Exception 1.

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R703.3 Wood, hardboard and wood structural panel siding.

R703.3.1 Panel siding. Joints in wood, hardboard or wood structural panel siding

shall be made as follows unless otherwise approved. Vertical joints in panel siding

shall occur over framing members, unless wood or wood structural panel

sheathing is used, and shall be ship lapped or covered with a batten. Horizontal

joints in panel siding shall be lapped a minimum of 1 inch (25 mm) or shall be ship

lapped or shall be flashed with Z-flashing and occur over solid blocking, wood or

wood structural panel sheathing.

R703.3.2 Horizontal siding. Horizontal lap siding shall be installed in accordance

with the manufacturer’s recommendations. Where there are no recommendations

the siding shall be lapped a minimum of 1 inch (25 mm), or ½ inch (13 mm) if

rabbeted, and shall have the ends caulked, covered with a batten or sealed and

installed over a strip of flashing.

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Table R703.4 & Section R703.4

R703.4 Attachments. Unless specified otherwise, all wall coverings shall be

securely fastened in accordance with Table R703.4 or with other approved

aluminum, stainless steel, zinc-coated or other approved corrosion-resistive

fasteners. Where the basic wind speed per Figure R301.2(4) is 110 miles per hour

(49 m/s) or higher, the attachment of wall coverings shall be designed to resist the

component and cladding loads specified in Table R301.2(2).

• Table R703.4 covers all prescriptive exterior weather-resistant siding

attachment.

• The requirements are broken down by siding material in the left column.

• The table also identifies attachment based on support for each material.

• Pay particular attention to the footnotes as applicable (a through z).

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Wall Covering – Exterior Table R703.4 & Section R703.4

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Wall Covering – Exterior Other specific requirements for exterior wall covering:

R703.5 – Wood shakes and shingles

R703.6 – Exterior plaster

R703.7 – Stone and masonry veneer

R703.9 – Exterior insulation and finish systems (EIFS)

R703.10 – Fiber cement siding

R703.11 – Vinyl siding

R703.12 – Adhered masonry veneer

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R703.8 Flashing. Approved corrosion-resistant flashing shall be applied shingle-

fashion in a manner to prevent entry of water into the wall cavity or penetration of

water to the building structural framing components and redirect it to the exterior.

Self-adhered membranes used as flashing shall comply with AAMA 711. The

flashing shall extend to the surface of the exterior wall finish. Approved corrosion-

resistant flashings shall be installed at all of the following locations:

1. Exterior window and door openings. Flashing at exterior window and door

openings shall extend to the surface of the exterior wall finish or to the water-

resistive barrier for subsequent drainage.

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Wall Covering – Exterior Flashing requirements for exterior walls (continued)

R703.8 Flashing…

Approved corrosion-resistant flashings shall be installed at all of the following

locations:

2. At the intersection of chimneys or other masonry construction with frame or

stucco walls, with projecting lips on both sides under stucco copings.

3. Under and at the ends of masonry, wood or metal copings and sills.

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R703.8 Flashing…


locations:

4. Continuously above all projecting wood trim.

Includes:

Windows

& Doors

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R703.8 Flashing…


locations:

5. Where exterior porches, decks or stairs attach to a wall or floor assembly of

wood-frame construction.

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R703.8 Flashing…


locations:

6. At wall and roof intersections. Kick-out flashings shall be installed at all wall and

roof intersections, such as where a lower roofline terminates against a vertical wall

[see Figure R703.8(1)].

7. At built-in gutters.

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