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Bolting your mud sill to the foundation and adding plywood to the cripple walls are the two most cost effective steps you can take to strengthen your home for earthquakes.

What to look for ...
To check your home's earthquake fitness, all you need is a flashlight and a willingness to get a little bit dirty. The place to start is in the crawl space underneath your home.

Is your house properly bolted down to its foundation?
The wood that rests directly on the foundation is called the mud sill. Until the 1940s, home builders often did not bolt the mud sill to the foundation. This creates a serious structural weakness that can allow your home to slide off its foundation during an earthquake. The mud sill should be bolted at four to six feet intervals and within one foot of every joint, but no closer than nine inches to the end of the board.

Do you need plywood on your cripple wall?
Check to see if you have a cripple wall and if it is braced with plywood. If the cripple wall is covered on the exterior with only stucco or wood siding, it is not strong enough to resist earthquakes. You will need to add plywood. Sheets of plywood nailed to the cripple walls help to prevent damage from shaking in this weak area of your house. Crossbracing within the framing is not enough.


Check for faulty materials in the concrete & wood framing
The foundation is a common area of structural weakness. When concrete foundations are porous or crumbly, they will not provide adequate strength to resist earthquakes. Unreinforced brick or stone masonry may need to be replaced or strengthened. An engineer or architect is required to design these types of repairs. Check to see if there is insect damage or dry rot in the wood. Faulty materials such as rotten wood and porous concrete should be replaced. Risky conditions in concrete include cracks wider than 1/8 inch, large voids, or 'honeycomb" concrete. If the concrete chips or flakes when you poke it with a screwdriver, it may be unsafe. NOTE: lf you suspect faulty material, you may need the assistance of a licensed engineer or architect to design a solution.