Earthquake Retrofitting Explained: House Bolting, Foundation Bolting and Cripple Wall Bracing

Posted October 16, 2019, under Blog

Earthquake retrofitting is a must if you own an older home in Los Angeles.

Earthquake retrofitting (sometimes called seismic retrofitting) is a reinforcement method that helps to keep your home secured to its foundation during a large earthquake.

Most homes in Los Angeles, and throughout California, that were not built in the last 20 years are likely lacking the structural reinforcement necessary to protect these properties during a massive earthquake. As the years have progressed – and especially after the devastating ‘94 Northridge quake – structural engineering and construction techniques have greatly improved.

There are various techniques that can provide earthquake retrofitting to a property – the most common forms of reinforcement are house bolting, foundation bolting and cripple wall bracing.

House and foundation bolting:

When it comes to house bolting and foundation bolting, this method uses skilled planning and placement to install foundation bolts to critical areas of the property. These bolts strengthen the foundation by connecting the wood framing of the home to its concrete foundation (otherwise known as the sill or mudsill). In homes that were poorly constructed, oftentimes the existing bolts were placed too far apart, and in older homes these bolts can become weakened over time. During your earthquake retrofitting inspection, your foundation specialist will identify what areas of your home’s foundation need reinforcement and what’s the best method for providing that.

Cripple wall bracing:

If your home has what’s known as a “crawl space” – an area of wood-framing located beneath the property, there’s a good chance your cripple wall will need to be braced for added reinforcement. During an earthquake, these wood-framed walls (aka cripple walls) are more likely to collapse during the back-and-forth and side-to-side shaking of a large earthquake. When the cripple wall collapses, then the home’s main floor will drop to the ground, destroying the property. Cripple wall bracing is another method of earthquake retrofitting that helps to brace the front and back of the plywood that runs beneath the property, to ensure it can withstand the intense shaking of a quake.

Soft story structures:

Homes are not the only properties in Los Angeles that need seismic retrofitting; apartment or commercial buildings that were constructed with a “soft story” typically need structural reinforcements. A soft story structure is a multi-level building with a room or first floor that sits on top of an open space (typically used for tuck-under parking). The opening of the bottom floor creates a “softness” in the structure, meaning it’s lacking the strength to withstand the lateral shaking of an earthquake. Soft story structures had the highest rate of collapse and destruction during the Northridge earthquake, which is why its been mandated by Los Angeles to retrofit these properties. A soft story structure can be reinforced by adding additional plywood bracing or the addition of a steel moment frame.

If you think you own a home that needs earthquake retrofitting or a soft story structure, contact Julian Construction today.

You can schedule a free inspection with us, where we’ll send over one of our qualified foundation specialists to inspect and analyze the area in order to determine the best way to strengthen the building.

To schedule a free inspection with Julian Construction, click here or call us now at 877-407-3876. A representative will review the information you provide and contact you to schedule your inspection.

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