By Shawn Kyles
An earthquake can cause serious damage to a home, especially if the building has not been retrofitted. Retrofitting is the modification of a structure by adding new components to make the building stronger. Following the 1994 Northridge earthquake, the severity of structural issues in residential neighborhoods varied considerably from house to house depending on the steps each homeowner had taken to fortify their home.
Statistics show time and again that during seismic activity, houses that have been retrofitted will have less damage than a home that hasn’t been reinforced. This was the case in the Long Beach earthquake of 1933, which resulted in the structural failure of brick buildings without reinforced masonry walls, including many school buildings in the area. Buildings with reinforced concrete had very little, if any, structural issues. In the aftermath of the magnitude 6.25 quake, California’s Riley Act was adopted, which required local governments throughout the state to establish building departments and inspect newly constructed homes and businesses. During the years that followed, new building codes were implemented requiring the bolting of any wooden walls to the structure’s foundation.
House bolting is a method of retrofitting in which a home is securely fastened to the foundation. It reduces the potential for earthquake damage by increasing the home’s resistance to ground motion. Any house built prior to 1950 that has not been retrofitted, will not be attached to its foundation; it is simply resting on the home’s concrete base. In an earthquake, structures like these can easily slide off of their foundation and collapse. Many of the homes that fell off of their foundation or were damaged during the Northridge quake were not bolted to the foundation.
Another way a home’s structural integrity can be improved is by bracing cripple walls. A cripple wall is the wall between the first floor of a home and the foundation. The walls create the crawl space that is often found underneath a home. Cripple walls are usually only covered by exterior wood siding or stucco, and are considered the weakest part of a building. Bracing the walls with plywood will increase their strength and help prevent the house from swaying during a quake.
If you are concerned about your home’s ability to withstand an earthquake, contact a foundation repair expert and request an inspection of your property. An experienced foundation professional will know the best way to retrofit your house, and can look for other foundation issues that may need to be addressed in order to minimize earthquake damage.