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Stem-Wall House

Two types of houses built before 1979—"stem-wall” and “cripple-wall”—may benefit from retrofitting with foundation anchoring, which reduces the possibility of a house sliding off of its foundation in an earthquake.

“Stem-wall” houses have a wood-framed first floor resting directly on a raised concrete perimeter foundation. The stem-wall retrofit consists of bolting the house sill plate to the foundation using foundation plates.

“Cripple-wall” houses have a short perimeter wall between the foundation and the wood-framed first floor. A cripple-wall retrofit consists of anchor-bolting the base of the wood frame to the concrete foundation and bracing the cripple walls.

Foundation Anchors: Bolting Raised Concrete Perimeter Foundations

“Foundation anchorage” describes both foundation bolts and foundation plates, and either can be used to secure a house frame to its foundation. For detailed information about foundation anchors, including which method to use, visit Earthquake Brace + Bolt.

New foundation anchorage can be installed by a licensed contractor according to a standard plan set for seismic retrofits, if your community has adopted such a plan set and your foundation meets plan-set requirements. Typically, Plan Set A is used in Northern California, and Standard Plan Set 1 is used in Southern California.

If your house does not have a raised continuous concrete foundation, or if it is not a wood-framed house, you should hire a licensed structural or civil engineer to advise on your retrofit efforts.

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