The Problem

Damage to home due to cripple wall failure.

Source: Office of Emergency Services

• 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

Diagonal Sheathing. Common in older homes.

Source: California Seismic Safety Commission

• 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.
• 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.

The Solution

Plywood panels nailed to the studs.

Source: California Seismic Safety Commission

• 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

• Detailed information for do-it-yourselfers or engineers can be found in the International Existing Building Code, published by the International Code Council
• Publication: How You Can Strengthen Your Home for the Next Big Earthquake in the Los Angeles Area, City of Los Angeles, Department of Building & Safety, October 2001.