Homes without cripple walls or soft stories are generally more stable in earthquakes compared to structures that have these vulnerable features. However, properties located in high seismic regions still benefit from additional reinforcements and seismic retrofitting to enhance structural resilience. Here’s a guide on the risks, considerations, and retrofit options for homes built without cripple walls or soft stories, and how homeowners can improve their seismic performance.

Cripple walls are short walls located between the foundation and the first-floor framing. While they elevate the structure, they are vulnerable to buckling or collapse during earthquakes, especially if they are not reinforced. Homes without cripple walls, where the floor framing rests directly on the foundation, tend to have a more direct, stable connection to the ground, making them less susceptible to lateral movement during seismic events.

A soft story occurs when a floor level (often the first floor) has large openings, like garage doors, that reduce its lateral strength. Soft stories are particularly vulnerable to collapse in earthquakes. Homes without soft stories lack these structural weaknesses, giving them a more uniform distribution of weight and reducing the risk of severe damage in an earthquake.

Even without the added risks of cripple walls or soft stories, homes in high seismic zones can benefit from targeted upgrades to strengthen the foundation and improve overall stability. Below are some recommended retrofit options:

Adding extra foundation anchors can strengthen the connection between the mud sill (the wood beam that sits directly on the foundation) and the foundation itself. Anchors help prevent lateral movement during seismic events, keeping the home securely attached to its foundation. Installing additional foundation anchors is a straightforward but effective retrofit option for homes in earthquake-prone areas.

Metal framing connectors improve the stability of key connections in the home’s sub-structure. Recommended placements include:

• Between Rim Joist and Mud Sill: The rim joist (outermost floor framing member) can be connected to the anchored mud sill to prevent detachment during shaking.

• Between Individual Posts and Concrete Footers: Adding connectors between posts, floor joists, and footers provides additional support to the structure, making it more resistant to lateral forces.

While some of these connectors are optional in a standard seismic retrofit, they are generally beneficial to include to maximize stability.

Chimneys are often more vulnerable than the main structure during an earthquake. Unreinforced chimneys can collapse or separate from the building, creating a safety hazard. Chimney bracing involves adding steel ties or brackets to anchor the chimney to the structure, reducing the risk of collapse. For homeowners who don’t use their chimney regularly, removal can be an alternative option to eliminate this seismic risk altogether.

For detailed seismic upgrade guidelines, homeowners can consult the Applied Technology Council’s report “Seismic Rehabilitation Guidelines for Detached, Single-Family, Wood-Framed Dwellings” (ATC-50-1). This pre-engineered plan set provides specific recommendations for reinforcing single-family homes, including those without cripple walls or soft stories. Additional resources for homeowners seeking earthquake protection include:

• Earthquake Brace & Bolt (California Residential Mitigation Program): This program offers grants to help cover the cost of seismic retrofits for eligible California homes. Visit Earthquake Brace & Bolt for more information.

• California Earthquake Authority: Provides earthquake preparedness resources and insurance options. Visit California Earthquake Authority.

• Quake Prepare: Offers tips and resources for securing homes against seismic risks. Visit Quake Prepare.

While homes without cripple walls and soft stories are structurally advantageous in seismic regions, additional retrofitting is often recommended for increased protection. Installing more foundation anchors, metal framing connectors, and bracing for chimneys can make the home more resilient against earthquakes. Consulting with a structural engineer can provide additional insights and tailored recommendations for your specific property.

Seismic retrofitting is a valuable investment, especially in high-risk regions, and helps safeguard both the property and its occupants. Regularly assessing and updating seismic detailing as needed can further strengthen the structure’s integrity and give homeowners peace of mind.