|III. Structural Problems and Strengthening
D. No Foundation Bolts or Insufficient Ones
Many older houses are not anchor-bolted to their
foundations or do not have enough bolts. Bolting was required in
the 1949 Uniform Building Code, but it was not uniformly enforced
by local governments until 1958. In a damaging earthquake, the
building can slide off its foundation. In new construction,
anchor bolts are embedded in the concrete foundation so that the
wall structure can be bolted to the foundation. To upgrade an
older house, expansion-type or epoxy-type bolts must be placed in
holes that are drilled into the foundation. The size and spacing
of the new bolts depends on the weight and orientation of the
house, and should meet local building code requirements.
Usually, the most difficult aspect of installing foundation bolts is drilling in a tight space. When there is a cripple wall at least 18" tall, holes for the bolts can be drilled using a rotary hammer. Shorter crawl spaces require a right-angle drill; this usually takes a little more time. The costs presented here apply to situations in which there are no existing bolts.
Typical Cost: $18/lf of foundation (right-angle drill)
Typical Cost: $12/lf of foundation (rotary hammer)
When the crawl space is minimal and the floor joist sits directly on the sill plate, the work is most difficult. In such a situation, holes cannot be drilled from above the sill. The house must be anchored to the sides of the foundation walls, provided that the existing walls are of adequate strength (you will need to consult with an engineer). This figure shows a possible solution to this tight access problem.
Typical Cost: $23/lf of foundation
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