Protect Your Property: Bolt Sill Plates to Foundation
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 complicated 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 is
bolting the sill plates of your house to its foundation to increase structural
stability. This is something that only a licensed contractor should do.
Bolt Sill Plates to Foundation
As shown in the figure, the sill plate of a house rests directly on top of the
foundation. (This figure shows the sill plate for a house built on a cripple
wall and crawl space foundation, a type of construction that is especially
susceptible to earthquake damage.) If the sill plate is not securely anchored,
an earthquake can cause it to shift on the foundation. When this occurs, there
is a greater potential for severe damage as well as injury to you and members
of your family.
One way to increase the stability of your house and reduce earthquake damage is
to have the sill plate bolted or otherwise anchored to the foundation. In the
method shown in the figure, bolts long enough to pass through the sill plate
and penetrate several inches into the foundation are installed every few feet
along the base of the exterior walls. This method is not limited to cripple
wall construction; it can also be used for a house built on a basement or
slab-on-grade foundation or on another type of crawl space foundation.
Tips
Keep these points in mind when you have the sill plates bolted to the
foundation:
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Modifications to the foundation of your house must be done by a licensed
contractor, who will ensure that the work is done correctly and according to
all applicable codes. This is important for your safety.
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Bolts are usually installed no more than 6 feet apart. The work involved is
likely to be extensive and may require that portions of the walls or floor be
cut away temporarily.
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Your contractor may be able to recommend an alternative anchoring method based
on other approved fasteners or connectors that can be installed with fewer
changes to your house and less work.
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If your house is built on cripple walls, you should consider bracing them after
the sill plates are bolted. For more information, refer to the separate
earthquake protection fact sheet titled Brace Cripple Walls.
Estimated Cost
Having a contractor bolt the sill plates to the foundation will cost you about
$50 to $75 per bolt, depending on the type of foundation you have. For example,
a house measuring 60 feet by 30 feet, will have a perimeter of 180 feet and
would therefore require a minimum of 30 bolts (if the bolts are placed no more
than 6 feet apart). So the cost for that house would be about $1,500 to $2,250.
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