Brace Cripple Walls to Prevent Collapse in Earthquake Shaking
03/24/2023
Make Resilient Upgrades | Strengthen Your Home • Earthquakes
Why do they matter?
Cripple (or crawl space) walls are relatively short frame walls that extend from the top of your home’s foundation to the bottom of the first floor. These walls typically enclose a crawl space or are part of a stepped foundation when a home is on a slope or uneven ground. During an earthquake, these walls become stressed and can fail, leading to severe building damage.
What do I need to know?
- Cripple walls are the most highly vulnerable of all light-frame walls because they must resist the shaking forces that act on the entire house during an earthquake.
- Older homes with cripple walls constructed without modern seismic building codes have weak connections between the wall and foundation because of the weaker sheathing type and inadequate attachment methods.
- Houses with stepped concrete or masonry foundation walls with unbraced cripple walls often fail in earthquake shaking.
- Decay, rot, and termite damage can also affect the cripple wall strength.
- Cripple walls are highly susceptible to earthquake damage; however, they are also one of the least expensive and easiest parts of your house to retrofit for improved seismic performance.
Where do I start?
- Before beginning your retrofitting project, inspect the existing cripple walls for rot, decay, or termite damage. Have all damage repaired and replace framing materials in areas where moisture is present or in contact with the foundation. Use pressure-treated lumber and decay-resistant materials.
- Anchor the base of the cripple wall (foundation sill plate) to the foundation, and anchor the top to the first-floor framing above.
- Cover, or sheath, the cripple wall with wood structural panels on the exterior or interior side of the crawl space walls.
- In general, cripple walls should not be higher than four feet in houses with crawl spaces or basements.
FEMA. Brace Cripple Walls.
FEMA DR-4193-RA2. Earthquake Strengthening of Cripple Walls in Wood-Frame Dwellings.