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2018 National Home Improvement Estimator, All Rights Reserved Page 502

Extra hold-downs will add earthquake resistance if the existing foundation is continuous reinforced
concrete or masonry. If the foundation isn't reinforced concrete or masonry, a structural engineer may
recommend a steel moment frame that can transfer loads to other parts of the building.

Bracing Hillside Homes
Beginning in the 1950s, it was common to see homes built over steep hillsides. Usually the main floor of
such a house is at street level. A system of stilts or tall wood-frame walls support the portion of the
home built over the lower part of the lot. In an earthquake, the floor framing can pull away from the uphill
foundation wall. Figure 18-7 shows a common result. An earthquake moved the home a step or two
down the slope. Today we know better ways to anchor a home securely to the uphill foundation. But
older hillside homes need extra protection from earthquakes.

The IRC doesn't include any approved design for reducing the risk of collapse in a hillside home. But an
engineer will recommend upgrades that include:

* additional hold-down connectors or adhesive anchors to tie each floor joist securely to the upper
level foundation, as in Figure 18-8.
* attaching bottom plates of stepped (or sloped) downhill cripple walls to the upper level foundation.
This is particularly important when the top of the side foundation is sloped rather than stepped.