THIS 10 MINUTE VIDEO GIVES YOU THE BASICS.

Cripple Wall Retrofit Basics

 

Do I Need a Cripple Wall Retrofit?

A cripple wall retrofit is the most common type of retrofit, especially when working with the Earthquake Bolt and Brace program. If your home has more than three steps to the front door, that’s probably the type of retrofit you need. However, if your home has less than 3 steps to the front door, you probably need a different type of retrofit.

What is a Cripple Wall?

HOME NEEDING A CRIPPLE WALL RETROFIT

THIS IS A GOOD EXAMPLE OF A CRIPPLE WALL. IF YOU HAVE MORE THAT 3 STEPS LEADING INTO YOUR FRONT DOOR, YOU PROBABLY HAVE A CRIPPLE WALL AND NEED A SEISMIC RETROFIT

BLOCKS INSTALLED BEFORE A CRIPPLE WALL RETROFIT

A TYPICAL CRIPPLE WALL.

The Mechanics of Cripple Wall Retrofits

COMPONENTS OF A CRIPPLE WALL BEFORE RETROFITTING

 
 Each of these components are connected to each much like the links in a chain.  Accordingly, a retrofit strengthens all the connections in a cripple wall.

THIS HOME FELL OFF A CRIPPLE WALL THAT WAS AROUND 6 FEET TALLCRIPPLE WALL COLLAPSE WATSONVILLE LOMA PRIETA 1989

Here are two homes where the cripple walls collapsed. As you can see, these houses fell several feet down off of their foundations (note the concrete steps on the left in the lower image) because of a cripple wall collapse, but otherwise remained intact (WHY??).

INSIDE HOUSE DAMAGE AFTER FALLING FROM ITS FOUNDATION

This is what houses look like inside when they fall from their foundations.

Step 1: The Plywood Connection

The illustration below shows how plywood in cripple wall retrofits keeps the cripple wall from collapsing. While there are many types of plywood, some are better than others. In addition, the size and spacing of the nails and the type of cripple wall framing impact the earthquake resistance of the plywood. This video describes how plywood prevents cripple wall collapse.

PLYWOOD PREVENTING A CRIPPLE WALL COLLAPSE

CONTRACTOR NAILING PLYWOOD

Step 2: The Bolt Connection

THE NEED FOR BOLTS IN CRIPPLE WALL RETROFITS

BOLTS PREVENT THE BRACED WALL FROM SLIDING OFF THE FOUNDATION

BOLTING THE BOTTOM OF THE CRIPPLE WALL (HIGHLIGHTED IN PINK) TO THE FOUNDATION KEEPS EARTHQUAKE FORCES (RED ARROW ) FROM CAUSING THE BOTTOM OF THE CRIPPLE WALL TO SLIDE OFF THE FOUNDATION.

Step 3: Shear Transfer Ties

Figure 3 shows a cripple wall bolted to the foundation with plywood on it. Shear Transfer Ties prevent the floor from sliding on top of the bolted and plywood braced cripple wall. Shear transfer ties attach the floor to the cripple wall. This is the final stage of a cripple wall to shear wall conversion.

HOUSE SLIDING OFF THE BRACED CRIPPLE WALL

All seismic retrofit guidelines require the installation of shear transfer ties. Be sure to use the right one – many shear transfer ties on the market don’t do anything at all in terms of earthquake resistance.

ATTACHING THE FLOOR TO THE CRIPPLE WALL WITH STEEL

THESE SHEAR TRANSFER TIES RESIST EARTHQUAKE MOVEMENT. THESE ARE VITAL TO ANY EFFECTIVE WOOD FRAME HOME RETROFIT.

Review of the Three Steps in a Cripple Wall Retrofits

THE THREE COMPONENTS OF AN EFFECTIVE SEISMIC RETROFIT

ALL OF THESE RETROFIT COMPONENTS WORK TOGETHER TO TRANSFER FORCES INTO THE FOUNDATION.

Do I Only Need to Retrofit the Cripple Wall?

99% of the time retrofitting the cripple wall is sufficient. However, a cripple wall retrofit is not effective if you have a hillside home.

More Information on Cripple Wall Retrofits

Converting cripple walls into shear walls is a complicated process that involves more advanced techniques than are shown here.