Earthquake Proof Your Home
For many of us living in California, thoughts of “The Big One” linger in our minds. Even more so today. How many earthquakes in the past seven days alone have you read about?
Also, I can't help but wonder about all the people affected after two significant earthquakes struck Mexico in a ten-day period. The first one, measuring at 8.2, was the most powerful Mexican quake in a century. The second one, a 7.1 magnitude earthquake, toppled buildings in the nation’s capital of Mexico City, killing many and destroying hundreds of buildings, including many residential homes.
Here are some quick earthquake statistics on the Mexico earthquakes. According to earthquake com, the 8.2 quake generated four times the energy of the 1906 San Francisco earthquake, which measured at a 7.8 on the scale. Southern California has not endured an earthquake greater than a 7.3 since 1857.
In recent years, as the concern of stronger earthquakes to come has grown, city and county officials continue to enact more stringent building standards. For example, many buildings are now required to meet the new safety guidelines. For many years, these were only "soft requirements." Specifically, in the city of Los Angeles, pre-1978 buildings must meet the city's building code for earthquake retrofitting.
These much more demanding building codes have led to a surge in retrofitting. But how does this relate to us, the everyday homeowner? To start, you can earthquake proof your home.
So, what exactly can you do to protect what may be your single biggest investment? There is quite a bit. Here are five retrofits that will better prepare your home to withstand an earthquake:
1. Bolt walls to foundations
Decades ago, many homes relied on gravity to remain centered on their foundations. For example, in the 1994 Northridge earthquake, some homes collapsed. Why? These homes slipped off their foundations.
That's why it's necessary to secure your home to its foundation. Although anchor bolts will fix this issue, beware of the generic term “bolted house." Some houses are not as earthquake-resistant as they should be. Building codes that use anchor bolts have been in force since the 1930s. But, bolts in older homes are positioned either too small or too far apart. Thus, they may not be appropriate for a large earthquake.
How is an anchor bolt installed? A contractor drills straight down through the sill plate using a hammer drill. Always use anchor plates rather than traditional round washers. That's because they tend to fold or split when subjected to seismic forces.
What should you do if there isn't access to the inside of a wall? You can use metal foundation plates instead of anchor bolts. Doing this will secure the wood frame to the concrete foundation.
2. Block and brace walls
It's also important to add blocking between studs. These short pieces of wood are placed between the wall studs. They are bolted to the sill plate (bottom plate). Placing diagonal braces also adds strength and stability to a wall. Bolting, blocking and bracing can run anywhere from $3,000 to $7,000 for an average-sized house. High deductibles are typical with earthquake insurance. So many homeowners consider this investment as well worth it.
3. Add wall sheathing
Stud walls covered with drywall or plaster are a problem in even smaller earthquakes. Adding a layer of plywood or sheathing to walls increases dimensional stability. But, it's important to use material that is thick enough to resist different types of movement. That would include lateral, rolling, twisting earthquakes.
4. Strengthen your house's foundation
Certain kinds of foundations are more vulnerable to earthquakes than others. Also, cracke
d and otherwise damaged foundations are particularly vulnerable to quakes. Some concrete block foundations have blocks filled with rebar and concrete. Others only use hollow blocks.
If you have hollow concrete blocks, then you should speak with a structural engineer. The engineer can help you to determine the best way to reinforce the foundation. In the past, contractors cut into the blocks, inserted rods and attached them to the sill plate. Today, bolts, mesh sleeves and epoxy can be used to strengthen a concrete block foundation.
Homes with post-and-pier foundations are also vulnerable to seismic forces. In earthquakes, the posts sometimes fail, leading to structural collapse. It is often possible to brace piers to make them more earthquake-resistant.
5. Minimize the potential for a gas leak
Remember the scene in the 10.0 Earthquake movie where many buildings are on fire after the massive earthquake? You can see the natural gas pouring out from ruptured gas lines that suddenly ignite. Currently, ordinances have requirements for houses to have an automatic earthquake gas shut off valve. This earthquake valve stops the flow of natural gas to homes when a 5.4 or greater quake occurs. If you own an older home, I'd recommend that you make sure that you have the appropriate earthquake valve. Also, make sure you have a Gas and Water Emergency Shut Off Tool, so you can shut-off your water and your gas manually, if need be.
There is a way to address the threat of ruptures at your house. You should have a licensed contractor install flexible gas lines. These lines are installed on water heaters, clothes dryers, stoves, and furnaces. Tremors can topple a gas water heater, so secure it to the wall with earthquake straps. These earthquake straps are a requirement in many areas, including Los Angeles County.
Mitigating Costs and Risks
Retrofitting a single-family house may cost approximately 1% to 3% of its value. Some variables often drive costs higher. Retrofitting is typical in hillside locations, basements, and rooms over garages.
Here's a great resource provided by the State of California, the Homeowner's Guide to Earthquake Safety, which includes some free printable earthquake worksheets. It's also called the Environmental Hazards and Earthquake Safety Booklet.
I've heard of government programs that sometimes offset the cost of retrofitting. For example, in early 2016, some homeowners in certain zip codes qualified for $3,000 in grants. These grants helped to offset retrofitting expenses.
I would also recommend that you consider earthquake insurance. You may already have it. Earthquake insurance offers homeowners another way to manage their financial exposure. The California Earthquake Authority (CEA) is a nonprofit organization. Besides being a great resource for earthquake preparedness, it provides earthquake insurance to California residents. CEA offers homeowners two types of policies - Homeowners Choice and Standard Homeowners. Check it out for more information on earthquake insurance companies, earthquake insurance costs and earthquake insurance deductibles.
For some homeowners, there is a discount. Insurance premium reductions will offset the cost of strengthening older homes. In fact, the Hazard Reduction Discount is now higher - up to 20 percent of the policy premium. That’s an attractive discount.
To review what steps you should take today:
- Read The Homeowner's Guide to Earthquake Safety, also called the Environmental Hazards and Earthquake Safety Booklet
- Retrofit your house
- Get earthquake insurance
- Prepare an earthquake survival kit for first aid after earthquake
Then look into either doing these yourself or hiring a professional:
- Bolt walls to foundations
- Block and brace walls
- Add wall sheathing
- Strengthen your house's foundation
- Minimize the potential for a gas leak