Ever since the Ridgecrest Earthquakes struck in July 2019, several friends and customers of mine have asked for my construction advice - they all want to know how to protect their homes from earthquakes. If your home was built before the 1970's and has a raised foundation, bolting down your foundation can help protect your home from earthquakes.
What is an Earthquake Retrofit?
An earthquake retrofit is a seismic retrofit, it's also known as a "brace+bolt retrofit", "house retrofit", "foundation bolting", "foundation retrofit", and simply a "boltdown". It is the process of improving the connection between the wood-frame and the concrete foundation of a house. Homes built after the 1920's (there's plenty of these in LA County) were simply nailed down to a foundation, but new building codes went into effect in 1980’s resulting in better foundation to wood-frame connections. Newer homes built after the 1980's are nailed down and they incorporate large bolts throughout the foundation to create a stronger connection. That means that houses built before 1979 have a weaker connection when compared to homes built in the 1990's.
Why Should I Retrofit My Foundation?
During an earthquake the ground moves and shifts from under the house, but gravity and inertia try to hold the structure in place, and that's when things begin to break. Homes and structures with weak foundation-to-frame connections tend to experience massive damage along entire sections of a home. This was the most common type of damage we encountered when our team visited Ridgecrest, CA and Trona, CA. We conducted field research on how single-family structures were affected by the earthquake.
We observed several red-tagged homes in Trona, and we found that once a small section of the foundation breaks free - the entire section of the foundation will break. Things can go from bad to worse if liquefaction induced lateral spread occurs (lateral spread is when the earth literally spreads open) because the foundation can immediately break off and "move" away from the home. Most single-story homes will likely not collapse, but they may be red-tagged if deemed unsafe. If the connection between the wood-frame and the foundation is severely damaged, you'll need to repair it in order to inhabit the home. Foundation repair jobs can quickly exceed $100,000. Retrofitting your home's foundation is one of the best ways to protect your home - better safe than sorry. A "pound" of prevention can provide a "ton" of protection (pun intended)
An earthquake retrofit can help prevent major damage to the structure by keeping the home's wood-frame (wall & floor frames) and the foundation attached in the event of an earthquake. Foundation-bolting costs can vary depending on the size of the home, size of foundation, and the condition of the foundation, but you can expect to spend anywhere between $5,000-$20,000 on average.
We Visited Ridgecrest After the Earthquakes - Watch Below.
We visited the city of Ridgecrest, CA and Trona, CA to observe the damage made by the powerful sequence of earthquakes. Our goal was to learn what the most common type of damage was and why it occurred. We also visited the Mojave Desert to observe the large scars created by the earthquakes.