Protect Your Property: Brace Cripple Walls
What You Can Do
Earthquake protection can involve a variety of changes to your house and
property -- changes that can vary in complexity and cost. You may be able to
make some types of changes yourself. But compli-cated or large-scale changes
and those that affect the structure of your house or its electrical wiring and
plumbing should be carried out only by a professional contractor licensed to
work in your state, county, or city. One example of earthquake protection, for
a house built on a cripple wall foundation, is bracing the cripple wall to
increase structural stability. This is something that skilled homeowners can
probably do on their own, provided they obtain any necessary permits.
Brace Cripple Walls
Some houses are built on cripple walls. As shown in the figure, a cripple wall
is a short wall that rests on the foundation and supports the floor and
exterior walls. If the cripple wall is not braced, it can shift during an
earthquake. When this occurs, there is a greater likelihood that your house
will be severely damaged and that you and members of your family will be
injured.
If your house is built on cripple walls, one way to increase its stability and
reduce earthquake damage is to brace the cripple walls. In this method,
horizontal blocking that consists of 2" by 4'' boards is added between the
vertical studs at the top and bottom of the cripple wall and, if necessary, at
other locations between the studs. New vertical studs can also be added if
necessary. Plywood or oriented strand board is then nailed to the interior face
of the cripple wall. Also, nails are added through the existing blocking
between floor joists to ensure that the floor is securely attached to the
cripple wall.
Tips
Keep these points in mind when you brace cripple walls:
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Check with your local building officials to see whether you need a permit to do
this work.
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Before adding any bracing, check to see whether the sill plate below the
cripple wall is bolted or otherwise anchored to the top of the foundation. If
it is not, you should consider having bolts or anchors added. Any anchoring of
the sill plate should be done before you add bracing. For more information,
refer to the separate earthquake protection fact sheet titled Bolt Sill Plates
to Foundation.
Estimated Cost
Bracing a 2-foot-high cripple wall will cost you about $1.50 per linear foot of
wall. For example, a house measuring 60 feet by 30 feet will have a perimeter
of 180 feet. So the cost for that house would be about $270. This figure covers
only the materials you will have to buy and excludes the cost of any tools you
use, building permit fees, and the value of your time. This figure also
excludes the cost of having a contractor anchor your sill plates. Also, bracing
higher cripple walls may require more lumber and therefore may be more
expensive.
Other Sources of Information
Seismic Retrofit Training for Building Contractors and Building Inspectors:
Participant Handbook, FEMA, 1995
Reducing the Risks of Nonstructural Earthquake Damage: A Practical Guide,
FEMA-74, 1994
Protecting Your Home and Business from Nonstructural Earthquake Damage, FEMA,
1994