Weak Cripple Walls

Larger imageDamage to home due to cripple wall failure.

Source: Office of Emergency Services

The Problem

  • Wooden floors and stud walls are sometimes built on top of an exterior foundation to support a house and create a crawl space.
  • These are called cripple walls and they carry the weight of the house.
  • During an earthquake, these walls can collapse if they are not braced to resist horizontal movement.
  • If the cripple wall fails, the house may shift or fall.

How to Identify

  • Go under the house through the crawl space, to see if there are any cripple walls.
  • If there are cripple walls, check to see if they are braced.
  • Larger imageDiagonal Sheathing. Common in older homes.

    Source: California Seismic Safety Commission

  • There should be plywood panels adequately nailed to the studs OR there should be diagonal wood sheathing. (See Diagonal Sheathing drawing at right)
  • If you have neither of these, the cripple walls are probably insufficiently braced or unbraced.
  • Horizontal or vertical wood siding is not strong enough to brace cripple walls.

Larger imagePlywood panels nailed to the studs.

Source: California Seismic Safety Commission

The Solution

  • Plywood, or other wood products allowed by code, should be nailed to the studs.
  • The following are important:
    • Type of wood product used
    • Plywood thickness
    • Nail size and spacing
    • Do not cover vents.
  • Consult your local Building Department for permit requirements before starting work.

How-to Resources

©2016 SCEC Southern California Earthquake Center @ USC