1x4 let in bracing

[Richard W. Washington]

When are they needed? I thought they were needed across exterior walls such as this one below in the garage. I know they are in detached garages?

[Claude Lawrenson]

Depends on type/sheathing material that is secured to the wood framed exterior walls. Let-in diagonal bracing is used with nonstructural sheathing to provide lateral resistance to a light wood frame. Prescriptive codes still allow: 1″x4″ diagonal bracing, diagonal board sheathing and plywood sheathing as wall-bracing options.

[Michael R. Boyett]

I agree with Claude. 2006 IRC says:

R602.10.3 Braced wall panel construction methods. The
construction of braced wall panels shall be in accordance with
one of the following methods:

1. Nominal 1-inch-by-4-inch (25 mm by 102 mm) continuous
diagonal braces let in to the top and bottom plates
and the intervening studs or approved metal strap
devices installed in accordance with the manufacturer’s
specifications. The let-in bracing shall be placed at an
angle not more than 60 degrees (1.06 rad) or less than 45
degrees (0.79 rad) from the horizontal.

2. Wood boards of 5/8 inch (16 mm) net minimum thickness
applied diagonally on studs spaced a maximum of 24
inches (610 mm). Diagonal boards shall be attached to
studs in accordance with Table R602.3(1).

3. Wood structural panel sheathing with a thickness not less
than 5/16 inch (8 mm) for 16-inch (406 mm) stud spacing
and not less than 3/8 inch (9 mm) for 24-inch (610 mm)
stud spacing. Wood structural panels shall be installed in
accordance with Table R602.3(3).

4. One-half-inch (13 mm) or 25/32-inch (20 mm) thick
structural fiberboard sheathing applied vertically or
horizontally on studs spaced a maximum of 16 inches
(406 mm) on center. Structural fiberboard sheathing
shall be installed in accordance with Table R602.3(1).

5. Gypsum board with minimum 1/2-inch (13 mm) thickness
placed on studs spaced a maximum of 24 inches
(610 mm) on center and fastened at 7 inches (178 mm) on
center with the size nails specified in Table R602.3(1) for
sheathing and Table R702.3.5 for interior gypsum board.

6. Particleboard wall sheathing panels installed in accordance
with Table R602.3(4).

7. Portland cement plaster on studs spaced a maximum of
16 inches (406 mm) on center and installed in accordance
with Section R703.6.

8. Hardboard panel siding when installed in accordance
with Table R703.4.

Exception: Alternate braced wall panels constructed in
accordance with Section R602.10.6.1 or R602.10.6.2 shall
be permitted to replace any of the above methods of braced
wall panels.

Commentary - Braced wall panels must be constructed according to
one of these methods and in the locations and
amounts required in Table R602.10.1. In accordance
with the exception, an alternative braced panel may be
substituted where allowed by Section R602.10.6.

[Richard W. Washington]

Thanks Claude & Mike. The wood structural sheathing board was installed on the exterior side so it's ok.