Page 158 - ICC IEBC 2018

APPENDIX C

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[BS] C104.2.5 Short horizontal brace. Where conditions to provide 1 / inches (38 mm) of penetration into
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exist that prevent installation in accordance with Section the horizontal brace.
C104.2.2, C104.2.3 or C104.2.4, the horizontal braces 3. Racking blocks shall be permitted to be fastened to
shall be permitted to be shortened provided that installa- any face or edge of horizontal braces between each
tion is as indicated in Figure C104.2.5 and all of the fol- web or truss vertical posts to which a horizontal
lowing conditions are met. brace is attached. Racking blocks shall be permitted
1. The horizontal brace shall be installed across not to be on alternate sides of horizontal braces. Racking
fewer than two framing spaces, extend not less than blocks shall be installed tightly between the lumber
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4 feet (1220 mm) from the gable end wall plus 2 / 2 of truss members or truss plates such that the gap at
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inches (64 mm) beyond the farthest roof or ceiling either end shall be not greater than / inch (3.2 mm).
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framing member from the gable end, and be fastened [BS] C104.2.7 Alternative method of installation of
to each existing framing member with three 3-inch- horizontal braces at truss ridges. Where conditions exist
long (76 mm) fasteners (#8 wood screws or 10d that limit or restrict installation of horizontal braces near
nails). the peak of the roof, ridge ties shall be added to provide
2. An anchor block shall be fastened to the side of the support for the required horizontal brace. The top of addi-
horizontal brace in the second framing space from tional ridge tie members shall be installed not greater than
the gable end wall as shown in Figure C104.2.5. 16 inches (406 mm) below the existing ridge line or 4
The anchor block lumber shall have a minimum inches (102 mm) below impediments. A minimum 2-inch
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edge thickness of 1 / inches (38 mm) and the depth by 4-inch (38 mm by 89 mm) nominal member shall be
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shall be at a minimum the depth of the existing roof used for each ridge tie, and fastening shall consist of two 3-
or ceiling framing member. Six 3-inch-long (76 inch-long (76 mm) wood screws, four 3-inch-long (76 mm)
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mm) fasteners (#8 wood screws or 10d nails) shall 10d nails or two 3 / -inch-long (89 mm) 16d nails driven
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be used to fasten the anchor block to the side of the through and clinched at each top chord or web member
horizontal brace. intersected by the ridge tie as illustrated in Figure C104.2.7.
3. The anchor block shall extend into the space [BS] C104.2.8 Interrupted horizontal braces. Where
between the roof or ceiling framing members not conditions exist that prevent the installation of a continu-
less than one-half the depth of the existing-framing ous horizontal brace then horizontal braces shall be per-
members at the location where the anchor block is mitted to be interrupted using the methods shown in
installed. The anchor block shall be installed tightly Figures C104.2.8(1), C104.2.8(2), and C104.2.8(3). For
between the existing framing members such that the interruptions that occur in the attic framing space closest
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gap at either end shall not exceed / inch (3.2 mm). to the gable end, nine 3-inch (76 mm) fasteners shall be
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used to connect each section of the interrupted horizontal
4. The use of omitted horizontal braces using the braces. For interruptions that occur in the second attic
method of Section C104.2.3 adjacent to a short hori- space from the gable end, six 3-inch (76 mm) fasteners
zontal brace as defined in this section is not permit- shall be used to connect each section of the interrupted
ted.
horizontal braces. For interruptions that occur in the attic
[BS] C104.2.6 Installation of horizontal braces onto framing space farthest from the gable end, three 3-inch (76
webs of trusses. Where existing conditions preclude mm) fasteners shall be used to connect each section of the
installation of horizontal braces on truss top or bottom interrupted horizontal braces. Horizontal braces shall be
chords they shall be permitted to be installed on truss webs continued far enough to allow connections to three exist-
provided that all of the following conditions are met. ing roof framing members as shown in Figure
C104.2.8(1), C104.2.8(2) or C104.2.8(3). Fasteners shall
1. Horizontal braces shall be installed as close to the
be spaced in accordance with Section C103.5.3. Horizon-
top or bottom chords as practical without altering
tal braces shall be the same width and depth as required
the truss or any of its components and not more than
three times the depth of the truss member to which it for an uninterrupted member.
would ordinarily be attached. [BS] C104.2.9 Piggyback gable end frames. Piggyback
gable end frames (gable end frames built in two sections
2. A racking block, comprised of an anchor block one above the other) shall be permitted to be retrofitted if
meeting the definition of “Anchor block” in Section either of the following cases is true:
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C102 or comprised of minimum / -inch (12 mm)
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plywood or / -inch (11.1 mm) oriented strand 1. The existing studs in both the upper gable end
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board (OSB), shall be fastened to the horizontal frames and the lower gable end frames to which wall
brace in the second framing space from the gable sheathing, panel siding, or other wall covering are
end wall. The racking block shall extend toward the attached are sufficiently in line that retrofit studs can
roof or ceiling diaphragm so that the edge of the be installed and connections made between the two
racking block closest to the diaphragm is within with retrofit stud(s).
one-half the depth of the existing framing member 2. Existing studs in the upper frame are not sufficiently
from the diaphragm surface. The racking block shall in line with the studs in the frame below and the
be attached to horizontal braces using six fasteners existing studs in the upper frame are 3 feet (91 cm)
(No. 8 wood screws or 10d nails) of sufficient length or shorter.

2018 INTERNATIONAL EXISTING BUILDING CODE ® 139
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