Root Causes of Poor Earthquake-Tolerant Construction

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The most common earthquake vulnerabilities in a home are unreinforced brick walls, cripple walls, a lack of sheathing, and a structure that is not bolted to the foundation. Unsecured appliances can also pose a risk of fire due to a broken gas line. TerraFirma can help you address these common structural issues and protect your investment in your home.

Unreinforced Brick or Concrete Block

Brick makes for a beautiful exterior but requires support to absorb the shaking and vibrations of an earthquake. Masonry like brick, tile, adobe, or decorative rock must be reinforced with bracings like rebar to withstand an earthquake. Unsupported load-bearing walls, exteriors, and other structures like chimneys are especially vulnerable to collapse. Mortar, which is used to hold bricks together, is also not strong enough to support a home without reinforcement: Masonry can collapse or peel away from the house, falling on structures, vehicles or people in the immediate surrounding area.

Cripple Walls

Cripple walls, which are common in houses built before the 1960s, extend from your foundation to beneath the floor of the house and receive the brunt force of an earthquake. Cripple walls are short, vertical wooden boards that support the floor - if you see short wood stud walls enclosing the crawl space of your home, you could have cripple walls. If your house is built on a slab without a crawl space or after 1960, it is unlikely to have cripple walls. In an earthquake, unreinforced cripple walls can sway from side to side or cause the house to fall. Expansion bolts, framing anchors, and foundation bolting can prevent a cripple wall from collapsing during an earthquake.

Lack of Sheathing

Sheathing is a layer of plywood that is nailed over the studs of your home, providing a solid surface upon which to nail tar paper, shingles, and siding. Older homes, particularly those built before 1900, were commonly built without sheathing - clapboard was often nailed directly to wooden frame of the house. In addition to providing much-needed insulation, sheathing keeps the building from shifting in an earthquake.

Unsecured Foundation

Does your house rest on a foundation of poured concrete? Was it built before 1975? If so, your home may be secured to the foundation with nails, gravity, and little else. When a home is not secured, an earthquake can cause it to slide off its foundation, rupturing gas lines and causing fires, among other structural damage. A quick visual inspection can often reveal whether your home is secure: Look for thick bolts and anchor plates that connect the frame to the concrete foundation in your crawl space or basement.

Unsecured Appliances

The greatest danger posed by an earthquake often isn't the shaking; rather, it is fire from a ruptured gas line. Because most gas and water lines are rigid, they can be torn from their connection points during an earthquake, and appliance feed lines are particularly susceptible to breakage when unsecured equipment moves during a quake. Strapping your water heater to the wall or floor and installing seismic protection for your gas meter can go a long way toward minimizing damage.

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