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.

Remember

• It is very expensive to lift a house, repair the cripple wall, and put it back on its foundation

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.

Larger imagePlywood or diagonal sheathing strengthens weak cripple walls. If your home has a cripple wall between the foundation and the first floor, and the wall is not braced with plywood or diagonal sheathing, the house may fall or shift off its foundation during an earthquake.

Source: California Seismic Safety Commission

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.