http://www.bayarearetrofit.com/ Houses on level lots without cripple walls still need a seismic retrofit, even if they are bolted to the foundation. If your house was built after 1950 or so, and you know it is bolted according to earthquake provisions of the building code with a half inch bolt every six feet, (which was and still is the code) then go to    • Retrofit bolted homes? See why Brand ...   to see how these bolted homes can benefit from a seismic retrofit.

However, many houses on flat lots do not have any foundation bolts; bolting did not become California State Law until the late 1950s. Up to then, some cities required house bolting, and some didn't. The way you find out is to crawl under your house, put your hand on top of the mudsill and see if you find any bolts. If they are spaced 6 feet apart then your house is bolted according to the current California Building Code. If not, you need a seismic retrofit that targets bolting the house to the foundation.

Houses on level lots without bolts are attached to the foundation with a type of retrofit bolting hardware peculiar to homes where the floor sits directly on top of the foundation. These homes usually only have 18 inches of crawl space under the floor so normal foundation bolts cannot be installed. This hardware has undergone rigorous testing and is certain to be effective in an earthquake and is the only retrofit hardware used by Bay Area Retrofit. Use of tested retrofit hardware is essential to a good retrofit. Another very important seismic retrofit components are called shear transfer ties, which are also thoroughly tested.

Some companies such as Quakebusters, EarthquakeSafety, and many others use a retrofit strategy called angle irons in lieu of the tested systems shown here. Angle irons are an untested system and are discussed in Video 13    • Angle Irons and Untested Earthquake R...