Top 10 Ways to Reduce the Risk of Earthquake Damage
Whether you live on the nation's west coast or the central United States, you are at risk of damage from an earthquake. The Insurance Institute for Business & Home Safety (IBHS) offers this Top 10 list of structural retrofits to help reduce the risk of damage when the ground shakes.
Top 10 Structural Retrofits
10: Brace Garage Door Openings
Garages are particularly vulnerable to earthquake damage, and especially if there is living space above the garage. The narrow walls on either side of the garage opening must be able to support the seismic load that is transferred from the roof and additional living space above the garage (if one exists) into the foundation below. In order for these narrow walls to support this load, they must be properly braced. Bracing these walls is usually done by using steel bracing or specially detailed plywood panels as recommended by a registered professional engineer.
9: Brace Chimneys
Until recently, most building codes did not require homes with masonry chimneys to be reinforced and braced to the structure. Chimneys that are not properly reinforced and braced have historically detached from homes and toppled, even during moderately sized earthquake events. If you are unsure if the chimney on your home has been reinforced and braced properly, it probably has not. A few adequately placed metal straps secured to structural members (floor, ceiling, and roof joists) will help brace your chimney. Also inspect your chimney for signs of significant cracking (greater than the width of a dime) along the mortar joints as well as ensure that mortar is in good condition and does not easily crumble when scraped with a metal tool. For specific details on how to adequately brace your chimney, See FEMA Publication232: Homebuilder's Guide to Earthquake-Resistant Design and Construction.
8: Strengthen Cripple Walls and Anchor the Building to the Foundation
Cripple walls are short wood frame walls that exist between the foundation and the first floor framing. Cripple walls are commonly found in wood frame structures that have a basement or crawlspace. Because the more ductile wood frame cripple wall is typically attached to a less ductile concrete foundation, the connection between these two dissimilar materials is vulnerable to earthquake related failures. If your home does have a cripple wall, there are ways to strengthen the wall so that the wall and the foundation will behave more as a single unit. To complete this retrofit, access to the cripple wall beneath the first floor framing is required. Install a minimum of 3/8" structural grade plywood or oriented strand board (OSB) to the inside of the cripple wall framing. While you will benefit more from bracing the entire cripple wall, if budget is a concern, simply brace the corners of the cripple wall. Ensure that all edges are attached to structural framing and be sure to drill air holes in the structure so that moisture is not trapped within the bracing.
Homes that are not properly attached to the foundation can move off their foundations during earthquakes. It's important that the building be connected to the foundation with anchor bolts or other steel connectors (including steel plates and straps) that secure the sill plate – the wooden board that sits on directly on top of the foundation- to the foundation. If your foundation is in poor condition, made of unreinforced masonry, or a post-and pier type foundation, check with a professional engineer for a suitable retrofit.
7: Protect Windows
A brittle material such as glass can fail suddenly during an earthquake, throwing shards of glass throughout a room and injuring those nearby. Tempered glass, similar to the glass installed in automobiles, is designed so that the glass will break but the pieces are less likely to be sharp, jagged pieces that will seriously injure someone. If you are considering a window replacement in the near future, look into replacing your windows with tempered glass. If your home improvement budget does not allow for window replacement, a much less expensive option is to install a protective film with a minimum thickness of 4 mils on the inside of your windows. The film can be purchased at any home improvement store or you can contact the International Window Film Association for the nearest distributor in your area.
6: Select Light Fixtures Carefully
Although a glass chandelier may be a nice addition to your dining room or foyer, you may want to consider other options if you live in an earthquake prone area. Light fixtures that hang from the ceiling will inevitably sway during an earthquake. More earthquake resistant light fixture selections include recessed lighting and track lighting. If your design tastes insist on hanging light fixtures, then choose a light fixture that hangs from a more rigid material such as plastic, aluminum or brass, instead of one that hangs by a chain. Also, the less the light fixture hangs from the ceiling, the less it will sway during and earthquake. Finally, make sure all light fixtures are properly installed, screws are fully tightened, and whenever reasonably possible, attach the fixture to a structural member for additional support.
5: Brace Water Heaters
The horizontal forces created by an earthquake have a tendency to ‘push’ over water heaters that are not braced to the structure. Once the water heater has been tipped over, the broken water pipe will flood your home and destroy floors, walls, furniture, and all of your family belongings. Your home is at an additional risk to fire damage if your water heater also happens to be powered by natural gas and the natural gas line breaks. Bracing your water heater is a simple and affordable way of eliminating this problem. All you need is 2 x4 wood blocking, heavy duty shelving brackets, various fasteners, plumbers strapping, along with a basic tool kit. Complete installation details can be found in the IBHS publication "Is Your Home Protected? A Homeowner’s Guide to Earthquake Retrofit."
4: Secure Appliances
Just as water heaters may shift and/or tip over, appliances such as refrigerators, stoves, dishwashers, and washing machines may suffer the same fate. Each of these appliances may be attached to water and/or gas lines that will cause serious damage to the structure if the line is disrupted. To decrease the possibility of this dangerous situation from occurring, anchor all of your large appliances to the wall using safety cables or straps and minimum 3/8' screw eyes that are attached to structural members. Ensure that the restraint is located in the mid- to upper-portion of the appliance to provide the greatest resistance to overturning. Also, replace all of your rigid appliance connections with flexible connectors and install automatic shut-off valves for both the gas and water supply system to further reduce the possibility of a water or gas line break.
3: Protect Personal Belongings
Whether it's a file cabinet full of important documents or your new plasma screen TV, all of your personal belongings are at risk of becoming disorganized or damaged during an earthquake if the items are not properly secured.
- Bookcases and other Storage Shelving
: To prevent these items from overturning, attach the furniture to a structural member using L-brackets or Z-brackets. It is recommended that a minimum of 3" long #8 wood screws are used for wood frame structures and a minimum of 3" long #8 screws with plastic anchors or 3/16" diameter masonry screws be used to attach the brackets to the wall. Place heavier items on the lower shelves to reduce the furniture’s center of gravity. Also, install wood, plastic, or metal ledge barriers to prevent items from falling off shelves. Lock the wheels on all rolling furniture, or better yet, remove the casters all together.
- File Cabinets and Kitchen Cabinets
: Purchase lockable file cabinets and attach the cabinets to the wall using the same method described for bookcases and storage shelving. Install self-locking kitchen drawers and cabinets, or purchase a locking mechanism, such as baby-proof latches. Although locks may seem a bit cumbersome at first, the small investment you spend on these locks can potentially save you from replacing hundreds of dollars worth of expensive kitchen dishes, glasses, and serve ware.
- Other Personal Belongings
: Secure heavy equipment such as TV's and computers to the furniture they are resting on by using an ample amount of hook and loop material such as Velcro®. Secure pictures and other valuable artwork to the walls using closed screw eyes instead of traditional picture hangers. Ensure the screw eye is attached to a wood stud and multiple screw eyes may be required depending on the weight of the item.
2: Protect Loved Ones
Creating an earthquake conscious environment in your home may make all the difference during the next earthquake. Rearrange the furniture in your home so that beds are kept away from windows that may break and large furniture that may overturn on someone while they are sleeping. Teach your family to "duck" or drop to the floor, take "cover" under a desk or table, and "hold" onto it. Put together an emergency kit for your family in the event you are without water or power. Know where your gas, electric, and water main shut offs are and know how to use them.
1: Renovate Wisely
If at any time you decide to renovate your home, keep in mind that there are several things that have aesthetic appeal that will also increase the risk of your home to earthquake damage. These include:
- Replacing large portions of walls with windows and glass doors.
- Adding large skylights or additional stories
- Opening large portions of existing floors, such as creating a two-story foyer.
- Additions that create an "L" configuration
If at any time you decide to do major renovations to your home, contact your local building code department to ensure that all building code requirements are being met. Also, if you are considering any of the above renovations, contact a registered professional engineer to determine that your new structure will have the ability to withstand earthquake forces in your area.
© 2012 Insurance Institute for Business & Home Safety