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.
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Failed Cripple Wall
Inadequate cripple walls, like the one pictured above, were a major point of failure in the Loma Prieta earthquake. Photo courtesy of Fine Homebuilding magazine. |
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 (Figure D).
The vent holes should be covered with 1/4" x 1/4" galvanized wire screen to prevent mice from entering the wall cavity.
Materials
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.
Homeowners guide to earthquake retrofit
APA, The Engineered Wood Association
