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Earthquake retrofitting a home is done to prevent displacement from the structure�s concrete foundation. This makes a building safer and less likely to suffer damage during an earthquake. Homes need to be retrofitted because construction techniques have greatly improved and the effects of earthquakes on structures are better understood now than when most homes were built. While there is no such thing as a standard cost for earthquake retrofitting a home, the average price is usually about 1 to 3 percent of the home's cost. Larger homes, those built on hillsides, and those with basements or rooms over garages will typically cost more to retrofit and may even cost $10,000 or more.
Why Retrofitting is Necessary
Any home that is 25 years or older will likely need to be retrofitted because of new understandings of the effects of earthquakes on buildings. Homes built in the 1990s or later typically already have earthquake-resistant features installed during construction. It's imperative that homeowners who live in active seismic zones have their homes retrofitted to prevent damage and injury. The process will also improve a home's ability to keep residents safe during an earthquake and homes habitable after a major disaster. In addition, retrofitting will greatly reduce repair costs after a seismic event and may even prevent damage entirely. Finally, retrofitting a home will reduce earthquake insurance premiums, which have increased dramatically in recent years. Moreover, most of these insurance benefits have also decreased, making it far more risky than ever not to retrofit a home.
Common Steps in Retrofitting
A professional needs to determine which type of retrofitting would be best for each home, depending on several factors. Common solutions include:
Cripple Wall Bracing
Many structures are built on cripple walls. Cripple walls are short walls that rest on a home�s foundation and support the floor and exterior walls. When these walls are not braced, they may shift during an earthquake. When this occurs, the probability of severe damage and injury to individuals in the home greatly increases. Bracing cripple walls strengthens structures by increasing stability, and the process typically helps minimize damage on homes. The average cost of bracing a 2-foot high wall is about $1.50 per linear foot.
Houses that aren't bolted to their foundation may move during an earthquake. Homes that move off their foundation may also cause gas lines to rupture, which may lead to fires. The cost of foundation bolting may vary. However, prices typically range from $250 to $5,000. The cost of repairing a foundation after an earthquake may be $25,000 or more. The bolting process requires that holes are drilled through the sill plate on a foundation and anchor bolts are installed. Sometimes, there isn't enough space to drill, and steel plates will also need to be attached. These bolts must be properly installed to be effective.
Anchoring to Mud Sill
The wood on top of the foundation of a home is called the mud sill. Prior to the 1950s, mud sills were not bolted to a home's foundation. This creates a huge structural weakness in a building � the building can slide off its foundation during an earthquake. Homes should be anchored to the mud sill in accordance with Uniform Building Codes, which requires bolts to be placed every 6 feet. Anchoring structures to the mud sill typically costs about $200 to $500 and can prevent thousands of dollars in damages.
Earthquakes occur suddenly and without warning. The motion on the earth's crust can cause severe damage to homes. Older structures are especially at risk because many were not built to resist shaking and moving. Strengthening homes may greatly reduce or completely eliminate damage to a home during these types of natural disasters, and it may also prevent injury and even death.