Page 627 - 2018 National Home Improvement

2018 National Home Improvement Estimator, All Rights Reserved Page 500

Cripple Wall Bracing
Any framed wall above the foundation and below the first framed floor is a candidate for extra bracing.
These cripple walls are highly susceptible to damage during an earthquake. Cripple walls in houses built
prior to about 1960 seldom have adequate bracing. The sheathing won't be structural grade panels and
may not be attached securely at both the bottom plate and the first floor. It's easy to upgrade cripple
walls for earthquake resistance.

Before starting the upgrade, check existing cripple wall framing for signs of decay. Replace any framing
lumber that appears to be decayed. Use treated lumber. Check to be sure there are enough foundation
anchors. Then apply structural panel sheathing to either the exterior or interior face of the cripple wall.
Sheathing and connections should meet IRC requirements for new construction. Figure 18-3 shows
cripple wall bracing details. The Association of Bay Area Governments (San Francisco) offers a detailed
plan sheet for bracing of cripple walls at www.abag.ca.gov

Apply 3/8" plywood or OSB panels to the interior face of cripple walls if there's enough room to work in
the crawlspace. If not, install panels on the exterior with nails spaced no more than 4 inches.
Reinforcing a poorly-braced cripple wall is probably the single most cost-effective improvement you can
make to protect a pre-1960 structure from earthquake damage.

Weak- and Soft-Story Bracing
Ground floors of older multi-story buildings seldom have adequate bracing. To reduce the risk of
earthquake damage, consider adding hold-down anchors at corners any time you remove interior finish
materials. Attach these anchors to the end studs (or other studs that have sheathing edge nailing). Sink
a vertical rod or bolt into the foundation below. See Figure 18-4. Removing a 16"-wide by 4'-high section
of drywall at each corner should provide enough working room.