Cripple Walls
Cripple walls, the short stud walls between the floor and foundation of
some houses, were one of the most common points of failure during the
Loma Prieta earthquake. Turning the cripple wall into a shear wall
reduces the risk of collapse during an earthquake.

Doing the Job
As with ordinary shear walls, panel installation should begin at the
corners.  The panels can be installed on the inside or the outside of the
cripple wall framing.  Panels should be placed horizontally on cripple
walls shorter than four feet and vertically on those four feet or higher.   If
the panels are installed on the inside of the framing, drill a row of
3/4-inch-diameter vent holes five inches above the sill plate and a
second row five inches below the top plate of the cripple wall.  The holes
should be centered between framing members for even and efficient
ventilation.  The vent holes should be covered with 1/4" x 1/4" galvanized
wire screen to prevent mice from entering the wall cavity.

APA Rated Sheathing or APA Rated Siding panels are recommended.

Common nails are used for sheathing panels. Hot-dipped galvanized box
nails are used for siding panels.

This page was originally published at
Failed Cripple Wall
Inadequate cripple walls, like the one pictured here, were
a major point of failure in the Loma Prieta earthquake.
Photo courtesy of Fine Homebuilding magazine.
Cripple Wall Shear Upgrade