Keeping Your Home Strong on Shaky Ground: Seismic Retrofitting

While California is certainly famous for its earthquake activity, the rate of seismic activity has been drastically increasing of late in Oklahoma, Kansas, and even New York. While most homeowners in these states shouldn’t expect massive earthquakes any time soon, it’s important to know that a succession of frequent, low-intensity quakes can cause nearly as much structural damages as the big ones. To best protect their investment, homeowners in areas prone to low-intensity-quakes should consider retrofitting their homes.

There are three different ways that earthquake forces can affect a home. The lateral, or shear,  forces cause a home to move from side to side in what is called a racking motion. Shear forces can also cause a house to slide right off of its foundation. Uplift forces, which are vertical forces that push a house up, causing it to crash back down, can cause a house to lift off the foundation altogether and overturn.

Regardless of the force or affect, the structural region of the house which are most prone to earthquake motions is the area between the first-floor joists and the foundation. Most seismic retrofitting involves creating a continuous load path between all the elements of the house.  This involves three basic types of structural reinforcement: bracing, bolting, and attaching.

Bracing the cripple walls, or the walls sections between the foundation and the first floor, will keep them from collapsing and dropping the house directly onto the foundation. Brace the cripple walls with sheets of plywood.

It’s also important to bolt the reinforced cripple walls to the foundation. This will keep the house from sliding off of the braced cripple walls and overturning.

The house floor should also be attached to the cripple walls, in order to keep the house from sliding off of the cripple walls. Bolting the floor to the cripple walls will keep the house from sliding off of them and overturning.

To learn more about seismic retrofitting, check out the Institute for Business & Home Safety’s seismic retrofit guide. If you’re interested in encouraging your local government to participate in a seismic retrofit incentive program, take a look at this FEMA resource.



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